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The purpose of this study is to identify healthy watersheds and characterize relative watershed health in a large forest-dominated basin. Water balance and water quality for watershed health assessment was investigated for Geum River Basin in South Korea using Soil and Water Assessment Tool (SWAT), which is a physically based hydrologic and water quality model. In order to predict the reliable available water quantity of the basin, The SWAT model was established by dividing the basin into 78 subbasins as standard watersheds and the water resource facilities of 2 multi-purpose dams and 3 multi-function weirs were considered. The SWAT model was spatially calibrated (2005-2009) and validated (2010-2015) using daily observed dam and weir inflows, evapotranspiration, soil moisture and water quality data. For the calibrated model, patterns and simulations of hydrology and water quality will be evaluated by analyzing the hydrologic responses (infiltration, evapotranspiration, streamflow, percolation, soil moisture, baseflow, and groundwater recharge) and influences of water quality (sediment, TN, and TP) change. The watershed analysis will be carried out to assess the watershed health. [ABSTRACT FROM AUTHOR]

The use of mesoscale climate models to dynamically downscale coarse climate data allows for the capture of processes influenced by land cover and topographic features. This is useful for hydrology modeling where catchment processes happen in a spatial scale that is not represented in global climate models. However, selecting proper parameterization setting for downscaling is crucial to modeling properly the climate variables of interest. In this work, we are interested in studying the long term changes of climate in the Baker River Basin and the Patagonian Northern Icecap (NPI), but before embarking on this it is important to identify at least one combination of physics in a climate model that performs well in our area of study. To these ends, we use the WRF model that combines two microphysics (WGS and TGS), two longwave radiation physics (RRTM and CAM), two shortwave radiation physics (Dudhia and CAM), three boundary layer physics (YSU, MYJ and QNSE-EDMF) and two land surface models (5-layer thermal and NoahMP). In total, we use twenty-four combinations of physics to run the model in a nested domain of 22.5 and 4.5 km. The forcing data selected to drive WRF is the ERA-Interim, which is a global atmospheric reanalysis from 1979, continuously updated in real time, produced by The European Centre for Medium-Range Weather Forecasts (ECMWF). Similar experiments have been done for low latitudes in South America, therefore, the results of this work will allow us to generate long term downscaled climate data series with physics that work properly in this region. [ABSTRACT FROM AUTHOR]

Hydrologic researchers, water managers, governments, and conservation organizations around the world face the challenge of developing innovative strategies to alleviate increasing pressures on freshwater resources. Many of these approaches and solutions require large amounts of data describing catchment and river characteristics at large scales, from regional to global, encompassing major river basins or multiple countries which may suffer from incompatible or differing data conventions among them. Seamless global hydrological data can provide a consistent and homogeneous coverage that allows for standardized analyses, and can establish baseline information in remote areas where little monitoring is available yet stakeholders need to address urgent issues in a timely manner.To enhance global spatial coverage and standardization of catchment and river reach information, we here introduce the HydroATLAS database. HydroATLAS provides a single comprehensive, consistent and organized, fully-global data compendium that gathers and presents a wide range of hydro-environmentally relevant characteristics at both sub-basin and river reach scales at high spatial resolution. The hydro-environmental attributes are compiled from publicly available data sources and are organized in six categories: hydrology; physiography; climate; land cover & use; geology & soils; and anthropogenic influences.Version 1.0 of HydroATLAS offers a total of 271 individual attributes grouped in 51 attribute classes. At the sub-basin scale, the information is associated with catchment polygons offered at 12 levels of nested subdivisions; at the highest level of subdivision HydroATLAS contains 10.4 million sub-basins with an average area of 130.6 square-km, representing all global land areas (excluding Antarctica). At the river reach scale, HydroATLAS encompasses information for 8.5 million line segments with an average length of 4.2 km, representing a total of 35.9 million km of rivers globally.HydroATLAS creates novel opportunities for large-scale model-based hydrological analyses or multi-variable statistical assessments of catchment and river characteristics. It is expected to be particularly useful in remote or data-poor areas. In a first application, a global river reach classification was produced which differentiates 127 river types globally. [ABSTRACT FROM AUTHOR]

In future warming scenarios, decreasing ratios of snow to rain will have implications on streamflow generation in mountain areas. One hypothesis is that warmer winter temperatures will lead to a reduced snowpack and an earlier and slower melt, potentially decreasing streamflow. Variations in streamflow will control nearshore fate as snowmelt timing may determine lake inflow mixing and seasonal variation in nutrient fluxes. However, the mechanisms controlling streamflow generation in mountain areas are still elusive. In this work we explore how different snow-to-rainfall ratios influence streamflow generation in seven catchments around Lake Tahoe. Lake Tahoe is a deep (500 m), oligotrophic lake, positioned at the snowline (1900m) in the Sierra Nevada Mountains (CA/NV, USA) and renowned for its clarity (average annual Secchi depth greater than 20 m). As a long-term study site, extensive data have been collected since 1967 on both the basin hydrology and lake conditions. The total watershed area is 800 km2 and the catchments we analyzed range in size from 15 to 140 km2. Daily streamflow data was obtained through USGS and daily SWE data from SNOTEL as well as Sierra Nevada Snow Reanalysis Data. Our preliminary analysis indicates that there is a significant variation in the amount of streamflow for different SWE to precipitation ratios (SWE2P). Snowmelt is usually slower in warmer years and there is less streamflow in years with a smaller SWE2P. It seems that there is a threshold of 500 mm where total streamflow starts to increase proportionally to winter peak SWE, below that threshold total streamflow is not sensitive to the amount of snow in the catchment. There are differences in both the SWE2P and on streamflow signatures of the catchments on the east and west sides of the lake. For its unique location and dataset, we believe Lake Tahoe data provides a good opportunity for further studies on climatic and physiographic controls of snowmelt and streamflow generation in mountain areas. [ABSTRACT FROM AUTHOR]

In a time of retreating glaciers, outburst floods from ice-marginal lakes are poised to becomemore prevalent as glaciers thin and tributaries detach. A detailed field-based investigation ofthe filling and drainage of one such lake, dammed by the 70-km-long Kaskawulsh Glacier inYukon, Canada, was conducted to characterize the role of the little-studied englacialhydrological system during these events. We deployed a variety of geophysical andhydrometeorological instruments in and around the ∼1 km2 lake to monitor thehydrology and dynamics of the lake—glacier system. By integrating the resultsfrom all instruments and surveys, we develop a conceptual model that describes theevolution of various storage reservoirs leading up to, during and following lakedrainage. From the beginning of the instrument record in June 2017, the subaerial lake filled at anaverage rate of 0.5 m d−1 before reaching a maximum volume of 9.9x106m3 on 17 August.GPS and timelapse imagery reveal vertical glacier displacements exceeding 25 m near the icefront and 3 m at a kilometer distance, as water is injected beneath a partially floating ice shelf.These data are used to estimate the evolution of the subglacial hydraulic potential, fromwhich a hydraulic seal and likely flood flowpaths are delineated. Abrupt changes in ice-shelfuplift rates, associated with the formation of fractures and faulting, are linked to aredistribution of englacial water. Near the surface, water pressures in multiple boreholesexhibit sudden changes of up to 15 m of head, while at depth, ice-penetrating radarreflection-power measurements indicate fast and slow adjustments in englacialwater storage. The onset of drainage begins within six days of a reversal in thesubglacial hydraulic gradient near the lake, whereby flow across 55% of the lakecatchment area is redirected away from the lake and toward the Kaskawulsh Glacier.Lake outflow discharge appears to increase exponentially over the course of ∼19days, before reaching an estimated maximum of 75-110 m3s−1 on 4 September.Radar data collected after the drainage event suggest that the englacial reservoir didnot empty entirely, hinting at a possible buffering role for the englacial drainagesystem. According to water-balance calculations, the subglacial and englacial reservoirs storeapproximately 55% and 22%, respectively, of the water in the catchment at peak lake level,compared to 23% in the subaerially exposed lake. In our conceptual model, the subaerial,subglacial and deep/shallow englacial reservoirs connect abruptly in a series ofhydromechanical events detected across multiple sensor types. The dynamic coupling ofthese reservoirs and the abrupt nature of connections between them represent anadvance in our conceptual understanding of outburst floods from ice-marginal lakes. [ABSTRACT FROM AUTHOR]

The geomorphic and climatic settings strongly influence the hydrology and sedimenttransport characteristics of a large river system. The mode, efficiency, and scale of sedimenttransfer in a catchment are controlled by the degree of linkages between the differentlandscape components (i.e. sediment connectivity). Therefore, the spatial analysis andcross-correlation of hydrology, and sediment connectivity are essential in order to developeffective sediment management strategies and to mitigate the associated hazards inlarge-sized catchments (103-104 km2), where systematic field investigations are not feasible.The upper Kosi basin covers an area of ∼52,731 km2 draining through Tibet and Nepal.Seven major tributaries namely, the Indrawati, Bhote Kosi, Tama Kosi, Dudh Kosi, Sun Kosi,Arun, and Tamor join at different points and the combined annual water and sedimentdischarge at Chatara is measured as 1546 m3/s and 101 million tonnes respectively before itdebouches into the plains of north Bihar, India. The rainfall in upper Kosi basin has largeregional and temporal variations due to considerable orographic contrast and the basinaverage rainfall at Chatara is 898 mm/yr. Observed discharge and sediment load data for ∼30years were analyzed and compared with the spatial sediment connectivity resultsderived from a topographic based index. This comparison helps to understand thespatio-temporal variability in sediment dynamics and its implications for floodhazard. The overall response of the Kosi basin towards sediment connectivity shows significantspatial contrasts among the sub-basins, and this is governed by several factors such aslanduse/landcover, slope and size of the basin. Our study reveals that out of ∼101 milliontonnes of annual sediment load at Chatara ∼40% is being transported from westerntributaries (Bhote, Indravati and Tama Kosi) and this confirms the that Bhote Kosi andTama Kosi are among the most dynamic and well-connected system. In contrast,the Tamor, a moderately connected system, contributes only ∼16% of the totalsediment load at Chatara. The remaining ∼44% is transported by other tributariesupstream of Chatara, the most important being the Arun (moderately connected),Dudh Kosi (highly connected) for which no independent estimates are available.Exceptionally high sediment flux is one of the most serious problems in the Kosi basin thatis linked to several river-related hazards and sediment connectivity analysis canbe extremely useful to understand sediment dynamics in such large river basins. [ABSTRACT FROM AUTHOR]

Long term climate development – e.g. up to 100 000 years or more – is rarely an issue for societal questions and planning. However, the nuclear waste management industry needs to demonstrate safety for humans and the environment for time scales way beyond common standards. This demand, together with a general scientific interest in climate and landscape development, provides an opportunity for cooperation between industrial organisations and the scientific community. By using specific site analogues, the conceptual understanding of site behaviour and future climate development can be explored for long time scales.Here we summarize and present methods used and data collected in the Greenland Analogue Surface Project (GRASP). GRASP is a catchment-scale field study of the periglacial area in the Kangerlussuaq region, West Greenland, focusing on hydrological and biogeochemical processes in the landscape. The site investigations were initiated in 2010 and have so far resulted in three separate data sets published in ESSD (Earth system and Science Data) focusing on i) meteorological data and hydrology, ii) biogeochemistry, and iii) geometries of sediments and the active layer, respectively. The three data sets, which are freely available via the PANGAEA data base, enable conceptual and coupled numerical modelling of hydrological and biogeochemical processes during present-day conditions. The results of such modelling are discussed in terms of short and long term changes in properties and process rates due to possible changes in climate conditions. Quantification and assumptions on future change are often based on model predictions. Such models require cross-disciplinary data of high quality; however, such data rarely exist. Biogeochemical processes in the landscape are highly influenced by the hydrology, which in turn is intimately related to permafrost processes. Thus, a multidisciplinary approach is needed when collecting data and setting up field experiments aiming at increasing the understanding of these processes. An important asset of the GRASP data is that all data are collected within the same, relatively small, catchment area. This implies that measurements are more easily linked to the right source area or process. Despite the small catchment area, it includes the major units of the periglacial hydrological system; a lake, a talik, a supra- and sub-permafrost aquifers, allowing biogeochemical processes in each of these units to be studied. The data from GRASP are used both with the aim to increase knowledge of present day periglacial hydrology and biogeochemistry, and also with the aim to predict hydrological and biogeochemical consequences due to future climate change. [ABSTRACT FROM AUTHOR]

Climate change scenarios predict fluctuations between periods of severe droughts and extreme precipitation mainly caused by atmospheric rivers. Some regions (such as California during water years 2015-2017) have already been subject to the transition between such end-member conditions. Impacts of these extremes on watershed hydrology are largely unknown, and are of great importance for resilient community planning for future water reserves. Due to the complexities of hydrological phenomena occurring at watershed scale, assessing these dynamics requires physically based models, which are extremely expensive in terms of computational time. We used High Performance Computing and a high-resolution integrated hydrologic model to investigate the complex nonlinear dynamics in response to climate change. We constructed and validated a model of the Cosumnes Watershed located in Northern California, a unique region given the un-dammed nature of one of the last freely flowing major rivers in California. The integrated hydrologic model serves to provide a complete picture of the hydrological components occurring at the regional watershed to basin scale, including snow accumulation and melting, surface runoff, groundwater infiltration, and also the exchange between surface water, vadose zone and groundwater. As a method of model validation, we performed several comparisons between model outputs and remote-sensing data. Comparisons include simulated SWE (snow water equivalent) versus SNODAS (Snow Data Assimilation System) and an alternative SWE map reconstruction method (Bair et al., 2016), soil moisture was with SMAP (Soil Moisture Active Passive), and actual evapotranspiration was compared with METRIC (Mapping Evapotranspiration at high Resolution with Internalized Calibration). Our results show that groundwater storage is decreasing despite the extreme precipitation due to groundwater pumping. With these simulations we are able to highlight regions of watershed most sensitive to climate extreme and anthropogenic activities. These analyses provide a better understanding of the physical phenomena occurring in the watershed, strengthening our knowledge of how the system may respond to these extreme conditions which might become the "new normal." [ABSTRACT FROM AUTHOR]

Long-term river flow data are instrumental in understanding the risks posed by fluvial flooding and drought events. They assist in providing greater understanding of the drivers of hydrological variability and are fundamental to contextualising extreme events and detecting emerging climate change signals. In many parts of the world, these insights are limited given the lack of long-term river flow records, which in turn limits the opportunity for robust planning decisions in the water sector. Here we link datasets that take advantage of data rescue efforts and paleoclimate reconstructions with rainfall-runoff modelling techniques, to develop river flow reconstructions at a monthly timestep. Using Ireland as an exemplar, gridded European temperature and precipitation datasets are used to reconstruct monthly flows from 1766 to present for 30 river catchments. Uncertainties in reconstructions from hydrological model structure and parameters are integrated using the Generalised Likelihood Uncertainty Estimation (GLUE) method. Reconstructions are validated through use of quality assured long-term precipitation series for selected catchments and an assessment of historical drought undertaken. We find that the methodology produces robust reconstructions of monthly flows that allow for detailed assessment of catchment responses to varying climatic conditions on monthly, seasonal and annual timescales. Despite the uncertainty associated with reconstructions, we find that the low flows signatures associated with notable historic drought events are identifiable in our reconstructions. Finally, we highlight that the datasets and methods used can be readily employed to reconstruct river flows in other European contexts. [ABSTRACT FROM AUTHOR]

Communication about water-induced hazards (such as floods, droughts or levee breaches) is important, in order to keep their impact as low as possible. However, sometimes the boundary between specialized and non-specialized language can be vague. Therefore, a close scrutiny of the use of hydrological vocabulary by both experts and laypeople is necessary. In this study, we compare the expert and lay definitions of 22 common terms and pictures related to water and water-hazards, to see where misunderstandings might arise both in text and pictures. Our primary objective is to analyze the degree of agreement between experts and laypeople in their definition of the used terms. In this way, we hope to contribute to improving the communication between these groups in the future. Our study was based on a survey completed by 34 experts and 119 laypeople.Especially concerning the definition of words related to water there are some profound differences between experts and laypeople: words like 'river' and 'river basin' turn out to have a thoroughly different interpretation between the two groups. Concerning the pictures, there is much more agreement between the groups. [ABSTRACT FROM AUTHOR]

The hydrology of rivers in the greater Himalayan region is influenced by several confounding factors such as rain, snowmelt, and glacier melt. The precise linkages of these factors to river discharge, however, is not clearly known and continues to be a topic of active research. Here, we use station-based daily river discharge data from Nepal to investigate spatio-temporal characteristics of 22 river catchments with areas ranging from 629 sq km to 43000 sq km in the Nepalese Himalayas. We make the following observations: (1) We find that the deseasonalized time evolution of river discharge in the Karnali basin in west Nepal is different from the rest of the country. The difference in hydrology corroborates existing literature on the Karnali basin - it is climatologically drier and economically poorer with most people living on subsistence agriculture. (2) Our analysis further reveals a nontrivial interannual variability, in particular the occurrence of several anomalously dry spring seasons in which river flow fell to 30% lower than the usual for that time of the year. (3) Further investigation of synoptic-scale climatological factors, which could potentially cause the anomalously low discharge, indicate changes in meridional wind in the north Pakistan region as a possible influencing factor. As an outlook we propose a new West Nepal Discharge Index, which provides a reliable indicator of interannual variability of the Karnali basin, after taking into account intra-seasonal and climatological trends. [ABSTRACT FROM AUTHOR]

Studies of spatial and temporal variation of Nitrate (NO3) and Dissolved Organic Carbon (DOC) concentrations in rivers can inform on the control of their exports by hydrological processes, soil biogeochemical processes and catchment characteristics (geomorphology, land use, etc...). However, such studies are often conducted on large river basins, in which in-stream processes obscure soil-to-stream processes and landscape effects. This study has two objectives: 1) characterize NO3 and DOC concentration dynamics on small headwater streams, and particularly their dyssynchrony, 2) identify their controlling factors.We used time series of public dataset on water quality together with spatial information on climate, soil, geology, hydrology, agricultural land, domestic pressures and landscape features from 185 independent headwater catchments located in Brittany, Western France. Rivers and streams have been monitored for NO3 and DOC concentrations between 2007 and 2017, with at least eight samples per year. Catchments sizes vary from 1 to 200 km² (median of 38 km²). We used Generalized Additive Models to describe seasonal variations of NO3 and DOC concentrations and flow rates and extract amplitude and phase metrics. Potential controlling factors were identified using a correlation analysis between seasonal metrics and hydrological and land use variables.Respectively for NO3 and DOC, 85% and 71% catchments present a significant seasonal cycle and amplitudes are 3.3 ± 2.1 mgN/L and 3.1 ± 1.7 mgC/L. Four groups of catchments were identified based on seasonal metrics. In group A, 66 catchments depict an anti-correlation between NO3 and DOC seasonal pattern. NO3 maximum occurs in winter synchronously with DOC minimum and discharge maximum, while NO3 minima and DOC maximum occur in autumn. In group B (12 catchments), NO3 maximum occurs in summer synchronously with DOC minimum and the lowest summer flows. Group C (64 catchments) shows an intermediate pattern with two annual maxima for NO3 (and two minima for DOC) occurring in winter and summer, but sometime with a lag time for the pattern of NO3. Group D (26 catchments) is composed of catchments without significant seasonal variation for NO3 and DOC concentrations. The spatial variability of seasonality was mainly explained by differences in hydrological reactivity and to a minor extend by differences in geological substrate characteristics. In catchments with lowest groundwater contribution and highest hydrological reactivity, NO3 and DOC seasonal fluctuations are high and correspond mainly to group A. In catchments with highest groundwater contributions, NO3 seasonal fluctuations are small and those of DOC strong (mainly associated with group B). These results indicated that water transit time through the catchment as a result of mixing between groundwater and sub-surface runoff is a key element explaining opposite seasonal patterns of NO3 and DOC. [ABSTRACT FROM AUTHOR]

Climate change is expected to increase precipitation in northern latitudes. Indeed, global observational data sets show statistically significant trends in precipitation averaged over land between 30°N and 60°N for the period 1901-2008. These changes would cause reduced salinity in the Baltic Sea, a semi-enclosed marginal sea with a large catchment area located in northern Europe. With the help of ocean simulations forced by historical atmospheric and hydrological reconstructions and local observations, we analyze the variability of sea surface salinity (SSS) of the Baltic Sea during 1850-2008. In line with other variables of the Baltic Sea water cycle, also the time series in SSS show low-frequency oscillations with a period of about 30 years. Hence, trends in absolute SSS are not significant on centennial scales. However, we found a statistically significant positive trend in the North-South gradient during 1900-2008 enhancing the sharp horizontal salinity gradient. With the help of sensitivity simulations, this change is attributed to local changes in the river runoff; the total annual river runoff to the Baltic Sea did not change. A detailed analysis of the individual rivers reveal increasing freshwater supply from the northernmost catchment indicating a footprint of the anthropogenic impact on salinity with consequences for the marine ecosystem and species distributions. [ABSTRACT FROM AUTHOR]

Rainfall-runoff models are widely-used tools in catchment hydrology. Their evaluation is mostly based on comparing observed and simulated discharge values. Various statistical objective functions have been proposed to evaluate the agreement between these time series. However, model evaluation that is based on statistical objective functions actually does not provide the modeller with much insight about how the model fails to represent the hydrology of the actual real-world system. Other, hydrologically meaningful indices or signatures have been proposed instead. Signatures are indicators that quantify hydrologic response characteristics of the catchment. They can also be regionalized and thus provide a potential opportunity for model evaluation in ungauged basins. Our study investigates how to best integrate hydrological signatures in an objective function for model evaluation. We test our ideas on a large and diverse sample of UK catchments. [ABSTRACT FROM AUTHOR]

There is growing recognition that new approaches, underpinned by more system-oriented decision support tools, will be required to facilitate development compatible with the Sustainable Development Goals (SDGs) and to prevent dangerous ecological breakdown. We demonstrate the potential of Integrated Assessment Models (IAMs) to inform strategic policy decision making at the regional level, helping to understand key trade-offs and secondary impacts. We document the Delta Dynamic Emulator Model (ΔDIEM), co-produced with stakeholders, to integrate ecosystem services and household wellbeing, being utilised by the Planning Commission of the Government of Bangladesh for its strategic long-term planning. The model is applied to the southwest coastal zone (pop. 14m) where high rates of extreme poverty prevail. The model's process-based simulations plausible future ecosystem services and their link to households has helped reveal potential dynamics and movements in extreme poverty as well as responses in different characterisations of poverty (e.g. permanent versus temporary/seasonal). A key power of the model is its ability to assess both the occurrence of, and potential responses to, risk transfer, a phenomenon which threatens adaptation and development success particularly in vulnerable river delta systems. ΔDIEM integrates the outputs of multiple established physically and process-based biophysical models, a number of newly developed process-based models simulating salinity levels and household socioeconomics and poverty with a deep stakeholder engagement process. Models that simulated areas outside the coastal zone (upstream hydrology and Bay of Bengal oceanography), are used as input scenarios (i.e. boundary conditions). Other complex biophysical models focusing on the coastal hydrology and water quality (Delft-3D, FVCOM, MODFLOW) are represented with computationally efficient statistical emulators in ΔDIEM to make tight coupling across the system elements possible. Agriculture and aquaculture are important livelihoods in Bangladesh. Thus a process-based integrated farming model (building on the FAO's CROPWAT model) was developed and included in ΔDIEM.We report results from our analysis of two proposed interventions on behalf of the Government of Bangladesh, General Economic Division (GED) using ΔDIEM. GED has responsibility for the strategic development of the delta coastline within Bangladesh and recently enacted the first draft of the Bangladesh Delta Plan 2100 (BDP2100). The BDP2100 contains multiple possible interventions, the majority of which are only in the very early stages of development. This work is assisting in prioritising and refining these proposals. The intervention we investigated included i) A proposed extensive polder network in the south-central region of the ii) Strategic development of a chronically waterlogged area of the delta. In both areas we highlight insights on its potential implications for biophysical change and the potential associated poverty and inequality, and on risk transfer between regions and populations. In doing so we demonstrate IAMs' growing potential to ask and explore key questions and scenarios about the functioning of integrated biophysical and socioeconomic systems, but also highlight some of their key weaknesses. [ABSTRACT FROM AUTHOR]

For more than two decades, the use of artificial neural networks (ANNs) in hydrology has become an effective and efficient alternative against traditional modeling approaches, i.e. physically-based or conceptual. These can take advantage of any type of available information to predict the hydrological response of complex systems, with missing data and limited knowledge about the transformation mechanisms. A promising area of application is the real-time prediction of flood propagation, which is essential element of early warning and early notification systems. In this work we focus to flash floods, considering as areas of application two medium-scale catchments in Greece with substantially different characteristics. The first one is the highly urbanized river basin of Kephissos (380 km2), which is the main drainage channel of the Athens Metropolitan area, while the second is the rural catchment of Nedontas, SW Greece (120 km2). Both areas have been recently equipped with automatic hydrometric stations, while online rainfall data are also available at a representative number of meteorological stations. For the two case studies we investigate several setups of ANNs, in order to predict the river stage at the catchment outlet for several lead times, using different combinations of input sets, by means of upstream stage and point rainfall data. [ABSTRACT FROM AUTHOR]

Wetlands have many functions and are very important to human life and ecosystems. To quantitatively preserve and manage wetlands, it is necessary to analyze the hydro-ecological changes and evaluate its function and sustainability. In this paper, we predicted the plant habitat according to the change of wetland hydrology and have proposed measures to effectively manage wetlands by evaluating future wetland functions and sustainability. In this study, we selected Binae wetland which is the riverine wetland in Namhan river basin. And then, we defined the Inundated Exceedance Probability(IEP) which is the probability of inundation of riverine wetland and analyzed in three aspects. (1) Based on the IEP, we analyzed the water level, inundation area, inundated depth, and inundation period considering climate change and predicted future plant habitat environment. (2) To evaluate the wetland functions, we proposed Modified Hydrogeomorphic method(Modified HGM). And we evaluated future wetland functions considering the change of hydro-ecological environment due to climate change. (3) To evaluated sustainability of Binae wetland, we proposed Wetland Sustainability Index(WSI) considering water environment change, weather and climate, plant and animal environment factors. As the study results, emergent and submerged plants are expected to maintain or increase their status because future(2040~2099) inundation period and areas are similar to or better than in the past(2000~2017). But in the near future(2018~2039), the average water level, inundated depth, inundation area decreased conpared to the past. It can be seen that the inundation period also decreases. Especially, it is considered that the area where the inundation period and area decreased can be changed from emegent or submerged plants to shrubs & woody plants. And, because wetland function and sustainability are both high, so they will continue to be maintained. However, Binae wetland has a poor future environment in hydrological function and sustainability of fish. So it is necessary to manage in its aspects. It is expected that methodology presented in this study will be a basic data to predict the plant habitat environment and evaluate its function and sustainability.Acknowledgment: This work is supported by the Korea Environmental Industry & Technology Institute(KEITI) grant funded by the Ministry of Environment(Grant 18AWMP-B083066-05). [ABSTRACT FROM AUTHOR]

Human activities exert an unprecedented reach on the biosphere, a reach that is strengthening in many respects due to climate change. There is a growing body of evidence highlighting that human activities have a direct impact on the global silica cycle. In addition to river damming and nutrient over-enrichment, land cover change is another important way by which humans are altering silica exports from terrestrial to aquatic systems. Understanding the controls on silica exports from terrestrial systems has direct implications for silica availability and carbon cycling in coastal receiving waters, due to the reliance of diatoms on silica. Due to rapid climatic warming, the Arctic is undergoing land cover change in the form of shrub expansion, increasing extent and frequency of wildfires, extended growing season length, and northern migration of the treeline. Moreover, permafrost thaw alters watershed hydrology by deepening flowpath lengths and soil-water interaction times. All of these changes are likely to alter rates of silica exchange between terrestrial and aquatic ecosystems. This talk will synthesize recent findings from the Alaskan Arctic demonstrating how rapid climate warming and associated shifts in watershed land cover and hydrology is altering silica cycling in terrestrial and freshwater aquatic systems. We will present evidence demonstrating that shrub expansion and wildfire both serve to increase the amount of silica sequestered in land plants, strengthening the magnitude of the terrestrial silica pump at local scales. Conversely, degradation of permafrost results and deepening of the active layer increases total silica exports from terrestrial systems via rivers at larger regional scales. It remains to be seen whether small-scale increases in silica retention via land plants can offset larger-scale silica releases from thawing permafrost over time. I will also address the implications of these results in the context of the global silica cycle. [ABSTRACT FROM AUTHOR]

Precipitation and soil moisture deficits are often used to characterize the nature of drought. Extended periods of an extreme meteorological event (precipitation deficits) result in a hydrological drought because of streamflow, groundwater and reservoir level reduction. The water deficits have an enormous impact on socioeconomic status and development. The percentile values in the range of Q70–Q95 are commonly adopted as the low threshold for perennial rivers (Kjeldsen et al., 2000). In this study, we quantified the critical dry up period (CDP) and streamflow severity due to extreme meteorological events over a set of 10 watershed located in South Korea. The TPHM, GR4H, and CAT hydrological models were calibrated against daily streamflow data using the Shuffled Complex Evolution algorithm considering similar objective functions. The CAT platform is used to set up the three hydrological models (Kim and Jang, 2017) which have been tested in several basins (Birhanu et al., 2018; Jang et al., 2016; Miller et al., 2014). We selected the Q95 of the flow duration curve compiled using daily streamflows of each watershed as a low threshold level to detect the CDP and seasonal streamflow deviations. The analysis revealed the CDP vary from 30 to 90 days and the streamflow deviations from the Q95 also responded differently in the wet and dry season. In addition, the streamflow deviations increased with increasing duration of precipitation and soil moisture deficits. The result will provide information to water managers, policymakers and other stakeholders regarding the duration and severity of streamflow to extreme meteorological events. Acknowledgments: This research is supported by the Research Program (20190101-001) of Korea Institute of Civil Engineering & Building Technology and by the Korea Environmental Industry & Technology Institute (KEITI) grant funded by the Ministry of Environment (Grant 18AWMP-B083066-05).ReferencesBirhanu, D., Kim, H., Jang, C. and Park, S.: Does the Complexity of Evapotranspiration and Hydrological Models Enhance Robustness?, Sustainability, 10(8), 2837, 2018.Kjeldsen, T. R., Lundorf, A., and Dan, R.: Use of two component exponential distribution in partial duration modeling of hydrological droughts in Zimbabwean rivers, Hydrological Sciences Journal, 45, 285–298, 2000.Kim, H.-J. and Jang, C.-H.: Catchment Hydrologic Cycle Assessment Tool - A User Guide, Korea Institute of Civil Engineering and Building Technology, Korea, 2017.Jang, C. H., Kim, H. J., Ahn, S. R. and Kim, S. J.: Assessment of hydrological changes in a river basin as affected by climate change and water management practices, by using the cat model, Irrigation and Drainage, 65, 26–35, 2016.Miller, J. D., Kim, H., Kjeldsen, T. R., Packman, J., Grebby, S. and Dearden, R.: Assessing the impact of urbanization on storm runoff in a peri-urban catchment using historical change in impervious cover, Journal of Hydrology, 515, 59–70, 2014. [ABSTRACT FROM AUTHOR]

Keywords:, extreme precipitation, paleoflood deposit, peat bog record, Holocene, northern Apennines, climate change, water cycle.A series of record breaking precipitation events have stricken the mountainous area of Emilia-Romagna Region (northern Apennines, Italy) over the last years. As consequence, several geomorphological processes, like widespread debris flows along the slopes and hyperconcentrated flood in the stream channels, shallow landslides and overbank flooding affected the territory, causing serious damages to man-made structures. The detailed study of these recent deposits compared with fossil peat bog and lake paleodeposits can provide useful insight to support a strong match between precipitation intensity and warm climatic phases in antecedent climatic periods, as expected by the increase air water vapour holding capacity at higher temperaturesHere we present the results of the field campaign performed in summer 2017 at Lake Moo a 0.15km2 peat bog located at an altitude of 1130m a.s.l. The chosen area has been affected, during the flooding of the upper Trebbia and Nure valleys 13-14 September 2015, by several high-density flows generated by the stream that flow into the plain. Our main assumption is that, in such a small drainage basin (area <2 km2), with favourable geologic and geomorphic characteristics implying advantageous sediment transfer into lake, high density flood can be triggered only by high precipitation intensity events (HPI) lasting a sufficient amount of time for water to infiltrate and mobilize large quantities of debris. The sedimentary succession (ca. 13 m-thick) was studied through the extraction of two cores and one trench. The facies/paleoenvironmental interpretation of the sedimentary succession, characterized by clusters of coarse-grained alluvial deposits interbedded with organic-rich silty clays and peaty layers, was achieved combining sedimentological and pollen data with pedological data and radiocarbon dating (AMS 14C). Observed depositional cycles, retrieved by Lake Moo cores and trench, were put in relation with other specific paleoclimatic proxies available in literature for the North-Apennine area. This comparison illustrate that the increase of extreme paleoflood (associated with coarse-grained deposits similar to the ones observed recently) correlates well with warm phases (at millennial scale), with a maximum activity in during the holocene thermal maximum. [ABSTRACT FROM AUTHOR]

Tropical areas are currently experiencing rapid environmental change due to the combined effects of climate change and human impact on the landscape. Climate variations in Southeast Asia play a key role in the global hydrological cycle, but past changes in the Asian monsoon system and its effects on local ecosystems are poorly constrained due to a shortage of well-dated palaeoenvironmental records that can provide a longer-term perspective on environmental change. This study investigates sediment cores from Tasik (Lake) Chini situated on the Malaysian Peninsular and provides the first lacustrine record of palaeoenvironmental change from the area. The flood pulse wetland is one of the few lake basins in the lowlands of this region and is of great ecological importance, contributing to the site's UNESCO designation. Tasik Chini comprises twelve interconnected basins with a hydrology dependent on monsoonal rainfall, therefore the lake is highly sensitive to variations in hydroclimate. Here, we provide new information on past environmental changes at Tasik Chini using the carbon isotope composition (δ13Corg) and Rock-Eval pyrolysis of sedimentary organic matter, diatom assemblage, elemental analysis, and chlorophyll and carotenoid pigments. An established chronology based on 14C and 210Pb dating shows that the cores span the last ca. 4.8 ka, covering the lakes inception as a permanent water body as well as a transition to higher sedimentation rates since the late 19th century. The multi-proxy record indicates large changes in organic matter production and preservation, hydrology, and water quality over the lake's history with the most pronounced variations occurring during the past 150 years, especially since the 1950s. Together, these proxies demonstrate major shifts in the Tasik Chini ecosystem that were most likely driven by a dynamic monsoonal system during the Middle to Late Holocene, and more recently initiated by anthropogenic catchment land use changes. This rare wetland record offers the potential to better understand past hydroclimate development in Southeast Asia and provide context for the human impact-related changes that have occurred, and are likely to continue, in this rapidly developing region. [ABSTRACT FROM AUTHOR]

The SCHADEX method (Paquet et al., 2013) is a reference method in France for the estimation of extreme flood for dam safety studies. It is based on a semi-continuous rainfall–runoff simulation process: hundreds of different rainy events, randomly drawn up to extreme values, are simulated independently in the hydrological conditions of each rainy day of a historical record. This allows the generation of an exhaustive set of crossings between precipitation and soil saturation hazards, which leads to compute a complete distribution of flood discharges up to extreme quantiles.Since its introduction twelve years ago, the method has been applied to more than 150 catchments in France and abroad, with two types of rainfall-runoff models:• Lumped models like MORDOR or GR4J. • Semi-distributed models in which the modeled catchment is divided into several altitude bands, like MORDOR-SD, HBV or DDD.To provide a better representation of the hydrological processes in large and heterogeneous catchments, a distributed modeling approach is advisable. In this respect, a distributed version of the MORDOR model has been recently achieved and documented (Rouhier et al., 2017). In the SCHADEX method, the simulated rainy events are drawn and affected to a probability as areal rainfall values, i.e. uniformly on the catchment. The application with a distributed model thus requires these areal values to be disaggregated at an adequate resolution to feed the distributed rainfall-runoff model. This disaggregation is done thanks to a catalog of rain field shapes in which a relevant one is chosen according to the intensity of the simulated event, its season, weather type, etc. This catalog can be built by two methods:• A spatial interpolation of observed rainfall build for each day of the 1948-2012 period (SPAZM, see Gottardi et al., 2012).• A stochastic spatial rainfall generator accounting for spatial and temporal dependencies in daily precipitation fields (Vaittinada et al., 2019).This study compares the extreme quantiles estimations provided by a "classical" application of SCHADEX (both with a lumped and a semi-distributed model), to a distributed application using different strategies for disaggregating the simulated events. Different features of the simulated floods will be compared in order to assess the contributions of a distributed approach (compared to a lumped one) and the sensitivity to the modeling options. It is illustrated with the example of Ardèche catchment at Sauze (south-east of France, 2260 km²). References:Gottardi, F., Obled, C., Gailhard, J., & Paquet, E. (2012). Statistical reanalysis of precipitation fields based on ground network data and weather patterns: Application over French mountains. Journal of Hydrology, 432, 154-167.Paquet, E., Garavaglia, F., Garçon, R., & Gailhard, J. (2013). The SCHADEX method: A semi-continuous rainfall–runoff simulation for extreme flood estimation. Journal of Hydrology, 495, 23-37.Rouhier, L., Le Lay, M., Garavaglia, F., Le Moine, N., Hendrickx, F., Monteil, C., & Ribstein, P. (2017). Impact of mesoscale spatial variability of climatic inputs and parameters on the hydrological response. Journal of Hydrology, 553, 13-25.Vaittinada, P., Blanchet, J., Paquet, E. & Penot, D. (2019). Space-time simulation of precipitation based on weather pattern sub-sampling and meta-Gaussian model. Submitted. [ABSTRACT FROM AUTHOR]

The objective of the Hydrological Atlas of Switzerland (HADES) is to provide a comprehensive and detailed insight into the hydrological conditions in Switzerland. It is aimed at practitioners, scientists and the general public. The HADES was launched as early as 1989 and was a printed atlas with thematic maps at a quite large scale of 1:500,000 until 2010. In addition, other products such as excursion guides and learning tools for schools have been created. The printed maps of HADES provide an excellent overview of the variability of hydrological characteristics in space. Parts of the original information, however, may disappear due to the generalization necessary for the cartographic representation. In addition, the representations are rather static from a temporal point of view as they are usually limited to a certain period of time. The new digital data and analysis platform (http://hydromaps.ch) has been designed to overcome these limitations. It enables the display of hydrological parameters on different spatial scales, which are connected to each other via a zoom function. The zoom levels are only limited by the spatial resolution and by the accuracy of the underlying data. On the time scale, the main focus is on long-term annual, monthly and seasonal averages representing climatology. The period can now be selected dynamically so that it is possible to compare different periods. Furthermore, maps of individual months or even events can also be called up for selected topics, in order to assess the deviations from the climatological mean values.On the spatial domain, more than 4000 catchments are pre-processed. Various hydrological parameters are available as spatial averages for each of these catchments. Within a catchment, for example, the parameters of the water balance can be compared. Furthermore, comparisons between different catchments are also possible. These few examples show the interactivity and usability of the new Atlas platform developed by the HADES project team. The HADES has been financed by the Swiss Federal Office for the Environment for over thirty years. It has made a successful transition from the analog static world in the 1990ies to today's digital dynamic world. It will continue to make a major contribution to Swiss hydrology. [ABSTRACT FROM AUTHOR]

Recently, there has been a growing interest in extreme drought in the hydrological impact assessment due to climate change, but most studies are either drought index based on weather information or development of drought prediction systems to monitor the status. Therefore, it is not enough to evaluate water resource availability that reflect watershed characteristics. In order to evaluate and predict the precise water resource availability during drought, it is necessary to evaluate the characteristics of the hydrological environment considering the artificial water use in the watershed. CAT (Catchment hydrologic cycle Assessment Tool, Kim et. al, 2017) was used to evaluate the characteristics of the hydrological environment. CAT provides tools for analyzing artificial water use such as water supply, water reuse and groundwater intake. In this study, the water resource availability of Boryeong-Dam watershed (163.6 ㎢), which is known to be an extreme drought region, was evaluated considering the complicated agricultural water use in the upstream region. Rainfall and observed inflow data were used from 1999 to 2016, and daily climate data such as mean temperature, relative humidity, wind speed, and duration of sunshine were used. Comparing the simulated runoff with the observed runoff in the upstream area of Boryeong-Dam watershed, the model efficiency was improved by more than 10 % compared with the existing simulated runoff without consideration of the agricultural water use. This is the result before parameter calibration. If the detailed water use such as groundwater intake is taken into consideration, the model efficiency will be improved more.AcknowledgementsThis research is supported by the Research Program (20190101-001) of Korea Institute of Civil Engineering & Building Technology and by the Korea Environmental Industry & Technology Institute (KEITI) grant funded by the Ministry of Environment (Grant 18AWMP-B083066-05). [ABSTRACT FROM AUTHOR]

Cooperation of the Danube countries in the area of hydrology started in 1961, hosting the first conference on hydrological forecast in Budapest. The conference took place even before the International Hydrological Decade was proclaimed (1965-1975). That 10-year program provided an important stimulus to international collaboration in hydrology, and after them, the International Hydrological Programme of UNESCO established. Since 1975, cooperation between hydrologists of the Danube River Basin has been conducted within the framework of the International Hydrological Programme (IHP) of UNESCO. Up to day, XXVII conferences derived hosted by different Danube river countries.At the beginning, cooperation was related to discharge forecast, but later on the research extended on hydrological bases of the water management. The results of scientific achievement were integrated and published in well-known monography »Hydrology of The River Danube« in year 1986. The monography is until now the major integrated approach on water regime of the Danube River and its tributaries. Inside the IHP UNESCO Committees cooperation, several common projects are going on supported by modest national sources. Some of research published in the book "Hydrological processes of the Danube river basin: perspectives from the Danubian countries".In the presentation overlook on the IHP UNESCO Danube Basin present with short description of the reports. [ABSTRACT FROM AUTHOR]

The complex hydrological network of the Indus River basin has provided water for agricultural purposes since the establishment of the first villages and complex urban societies in the area (the Indus Civilisation, c.4.6-3.9 kyr BP). To understand precipitation patterns and variability during the transient Holocene and to investigate a possible multi-decadal drought toward the end of the Indus Civilisation apogee, we use climate model simulations to study precipitation seasonality and changes in climate dynamics. PMIP3's models simulate a large range of changes across the Holocene, and includes an even larger variability in the representation of the present day climatic mean. Therefore, we have developed metrics characterising present day precipitation variability that can assess climate model abilities and have the potential to statistically correct their results.The northern part of the Indus River basin is a buffer zone between extra-tropical westerly activity and south-easterly monsoon influence that overlaps with major orographic features. We investigated the atmospheric dynamic associated with each component, as well as their coupling, mainly using ERA-Interim reanalysis at daily, monthly and annual timescales. We first show that orographic-led wind convergence alone is sufficient to explain precipitation generation at the basin scale, with little variability between the seasons. Then we characterise the influence of upper-level western disturbances on winter precipitation. We also show that summer synoptic activity is affected by a tropical/extratropical interaction. Finally, we address the question of large-scale teleconnections and inter-annual variability in relation to previous results. [ABSTRACT FROM AUTHOR]

Understanding the urban hydrology of Oslo, Norway, is hampered considerably by a paucity of reliable data describing the urban runoff response to rainfall under varying degrees of urbanisation in different areas within the city. This knowledge is nevertheless critical for quantifying the potential benefits of low-impact flood mitigation measures, such as green roofs and rain beds. The modelling approach needed is akin to Predictions in Ungauged Basins in that parameter parsimonious models adaptable to local conditions are required and model 'calibration' involves the use of alternative data sources for building the hydrological model. In the SURF (Sustainable URban Flood management) project, we are applying a parsimonious rainfall-runoff model, DDD (Distance Distribution Dynamics), to quantify the water balance and runoff response in two contrasting urban catchments. One catchment is a typical residential area with detached houses and gardens, whereas the other is situated in an older part of Oslo, and is densely populated with blocks of flats and a park. The fraction of impermeable area (defined as roofs and roads) is 17% and 42%, respectively for the two catchments. In the DDD model, the distribution of distances from points in the catchment to the river network is an essential factor describing the runoff dynamics. As the natural drainage network is disrupted by urbanisation in both catchments, a GIS-derived surface flow network, with areal support such that it resembles the road network, serves as a proxy for estimating the distance distribution for the model. Runoff data for a partial calibration of the response to precipitation is derived from flow data from points within the combined sewer systems within the catchments. As information on sub-daily water usage is not available for the sewer points, a novel signal processing technique has been used to extract the wastewater flow from the runoff series. Preliminary modelling results indicate that the DDD model can successfully reproduce the residual runoff using these data sources, together with an hourly rainfall series, in a model calibration. The primary goal of the project is to identify the minimum level of data required for producing hydrological simulations useful for municipal authorities and planners. [ABSTRACT FROM AUTHOR]

The parameterization of hydrological models in ungauged catchments remains challenging. However, the increased availability of large data sets in recent years provides new opportunities for regionalization. In this study, we use the CAMELS dataset and the HBV model to simulate runoff in nearly 600 catchment areas in the United States. The HBV model was calibrated for all areas, and the calibrated parameter values were related to catchment characteristics. To account for parameter uncertainty, 100 independent calibrations were performed, and then median values and percentile ranges were used for the further analyses. For the simulation of runoff in ungauged catchments, we evaluated the use of regression equations compared to the transfer of complete parameter sets based on similarities between catchments leads to better model simulations. Additionally, we tested the added value of single discharge observations, which we pretended to be available. The regionalization approaches were furthermore benchmarked by runoff predictions using random parameter sets.First results indicated that the use of an ensemble with parameter sets calibrated in one of the other catchments leads to clearly better simulations than the use of randomly selected parameter values. Surprisingly, however, a hydrologically based selection of catchments – and the transfer of the corresponding parameter values – did not lead to better simulations than using the ensemble with parameter sets from all 600 catchments. Overall, this study indicates possibilities and limitations of regionalization with the help of large data sets. [ABSTRACT FROM AUTHOR]

Knowledge about the origin and transformation of nutrients at different temporal scales in theriver ecosystem could provide a better understanding of nitrogen (N) cycles in the rivers andhave important implications for regional and global N cycling. In this study, a multi-isotopeapproach (δ13C, δ15N and 210Pb) was used to investigate the factors affecting seasonal andlong-term changes in N sources apportionment and N biogeochemical processes in theBeijiang River located in the Pearl River Basin, China. Sources apportionmentby a Bayesian model (Stable Isotopic Analysis in R, SIAR) showed significantseasonal variations. During the flood season, the dominated origins were non-pointsources such as soil N for dissolved nitrogen (DN, accounting for 38%), soil organicmatter for particulate organic matter (POM, 58%) and sedimentary organic matter(SOM, 31%) due to intense precipitation. During the non-flood season, fertilizerdominated in nitrate source (48%) and effluent detritus predominated in the POM (47%)and SOM (32%) pools. N transformation between the DN, POM and SOM wasinfluenced by seasonally variable hydrology. Our data suggested low discharge wasmore favorable for vertical mixing of the water column and sedimentation, whichwas evidenced by similar δ15N values in the DN, POM and SOM in the non-floodseason. A sedimentary history record of 65 years (1951-2015) showed the variation ofnitrogen in sediment was mainly affected by human activities. From 1999 to 2005, adecrease trend in δ15N value was observed due to promotion of aquatic plants growthafter impoundment of reservoir. From 2005 to 2011, the enrichment in δ15N wascaused by an increased in sewage and waster emission due to the development oftourism industry. From 2011 to 2015, the rising of pollution treatment fund bygovernment improved water environment, resulting in δ15N-depleted in sediment. At65-years temporal scale, increasing temperature and CO2 concentration had lessimpact on N cycles in river ecosystem, however, high discharge could increase Ncontents and flood events might increased δ15N values in sediment. The results alsoindicated that δ15N was more effective than δ13C on source distinguish at 65-yearstemporal scale. This study provided more detail information regarding the nutrientssources and improved our understanding of the N cycling processes at differenttemporal scales in the river ecosystem, providing a better understanding for N cyclesin the river ecosystem and a scientific basis for water environment management. [ABSTRACT FROM AUTHOR]

Beaver (Castor fiber, Castor canadensis) are mammalian ecosystem engineers, modifying rivers and floodplains, and influencing local hydrology, geomorphology, carbon and nutrient cycling, and ecology. They construct dams, dig canals and burrows, fell trees and introduce wood into streams, which in turn impounds water and raises shallow water tables, altering the water balance, sediment transport, channel pattern, and biogeochemical cycling within aquatic-terrestrial habitats. In this cross-disciplinary study, we first synthesize beaver effects on the local hydrology, geomorphology and biogeochemistry of aquatic-terrestrial ecosystems. We then summarize results from four beaver sites in Switzerland and Germany in terms of hydrology, water biogeochemistry (nutrients, pH, dissolved oxygen, water temperature), geomorphology, dissolved/particulate organic matter concentration and composition (absorbance and fluorescence measures coupled with parallel factor analysis (PARAFAC) and RockEval-pyrolysis), macroinvertebrates (diversity, stable isotope analysis) during a complete hydrological cycle (all seasons). Results include a nitrate reduction of 17-23 % along beaver cascades, a DOC increase downstream of beaver reaches, a carbon storage increase in beaver sediments, and a spatial heterogeneity increase in macroinvertebrate food webs. Key feedbacks and overlaps among changes induced by beavers hint towards modifications in longitudinal connectivity (using drone-based remote sensing) that drive important process feedbacks. The magnitude of these feedbacks was heavily dependent on climate-landscape context as well as the ability to promote lateral connectivity determining the spatial extent of beaver effects with increasing stream order. We view these results in the context of stream management and restoration, and highlight the importance of a data-based, realistic approach towards using beavers for natural catchment management. [ABSTRACT FROM AUTHOR]

The changes in watershed hydrology are influenced mainly by two factors i.e landuse/landcover and climate variability. Hence, quantitative assessment of the effects of landuse/landcover and climate change is imperative for water resources management at river basin-scale. In the present work, a distributed hydrologic model SHETRAN is utilized to assess the relative impacts of landuse change and variability in climate on hydrology (streamflow and evapotranspiration) of a small wet tropical humid catchment (Vamanapuram river basin having an area of 787 sq.km) in Southern part of India. The past landuse changes within the river basin were identified using landuse maps for the years 1985, 1995 and 2005. In order to analyze the effect on streamflow and evapotranspiration of the river basin, three scenarios were generated in the study which included assessing i) the effect of only landuse change under a constant climate, ii) the effect of varying climate while maintaining constant landuse and iii) integrated effect of both varying climate and landuse change. The values of statistical indices such as Nash–Sutcliffe efficiency (NSE), ratio of root mean square error to measured standard deviation (RSR) and Percent bias (PBIAS) along with the visual comparison of observed and simulated streamflow indicated the capability of SHETRAN model in evaluating hydrological changes within the analyzed catchment. The main changes from 1985 -2005 were: increase in built up land by 97%, increase in grassland by 28%, decrease in mixed forest by 8%, and decrease in cropland by 12%. Due to landuse landcover change, the streamflow increased by 30.5mm/yr (3%) whereas the actual evapotranspiration decreased by 29mm/yr (2.4%). The variation in climate increased streamflow by 113mm/yr (10.7%) and increased evapotranspiration by 19mm/yr (1.56%). Combined effect of climate and landuse change increased streamflow by 139mm/yr (13%) and decreased evapotranspiration by 9mm/yr (0.8%). The influence of climate variation on hydrology of the river basin was more pronounced compared to the landuse change during 1985-2005 in Vamanapuram river basin. [ABSTRACT FROM AUTHOR]

Without careful land management, agricultural land in karst systems can pollute water courses, with polluted waters travel quickly to and through the sub-surface in karst systems. However, detailed understanding of how rapidly nitrate moves within the karst critical zone (from soils to aquifers) is limited by low resolution sampling for this highly-transmissive system. To understand nitrate behavior and its controlling factors, we deployed sensor technology at five sites to generate autonomously high-resolution time series of discharge and [NO3−N] in a farmed karst catchment in SW China. The [NO3−N] time series exhibited rapid response to rainfall-induced increases in discharge and a large magnitude in [NO3−N], ranging from 0.72 to 16.3 mg/L. The highest mean [NO3−N] and normalized annual fluvial export were observed in one headwater catchment with well-developed conduit structure. Elsewhere this was less-pronounced due to buffering by the karstic aquifer network as the contributing catchment area increased with distance downstream. Clear seasonal variation in NO3−N export occurred in response to source availability, most notable in catchments with valley agriculture: up to 97% of nitrate was exported from the headwater catchment in the wet season, with much of that loss occurring in only a couple of months, compared to 61% of nitrate exported at the larger catchment scale. The sensor time series showed that the aquifers were chronically polluted with nitrate. [ABSTRACT FROM AUTHOR]

Permanent water bodies are rather exceptional in the Kalahari under today´s arid climate. However, there are drainage basins, indicating large lakes existed at least since the Middle Pleistocene during more favorable periods. One example is the paleolake Tsodilo, embedded within a linear dune system at the Tsodilo Hills, 40 km west of the Okavango panhandle in northern Botswana.The aim of the study is to reconstruct the up to 70 km² large paleolake for the period of around 44-19 ka as a dynamic ecosystem, including variations in climate, weather conditions and environment. We investigate geomorphological processes which are the base for a paleohydrological interpretation of the proxy time series, especially regarding the local feedbacks within the sediment cascade. The morphostratigraphy will help to separate climatic from non-climatic processes affecting the hydrology of the ecosystem. In order to derive a morphostratigraphical model, we focused on a multi-methodological approach for surface and subsurface topography analyses. Basin-wide, a filtering procedure with discrete wavelet transformations (DWT) was applied at different spatial levels to a high-resolution Digital Elevation Model (TanDEM-X 12 m) to detect possibly hidden patterns. However, the accuracy of the DEM is strongly influenced by the spatial variation in density and height of the savannah type vegetation as well as changing soil properties in the catchment. In order to filter random, vegetation and soil-related signal parts, different DWT were applied and inverse DWT then provided a significantly noise-reduced DEM. For model evaluation, ground control D-GPS measurements were used. This method enabled us to extract hidden paleo-drainage channels, paleo-shorelines and -fans. The former shorelines indicate at least three different lake phases. Furthermore, parts of the drainage features appear as positive forms, leading to the hypothesis of relief inversion. We successfully tested the hypothesis by the combined application of seismic refraction and ground penetration radar and got deeper insights into the sediment structure and thus the geomorphological evolution.Additionally, four pits were sampled to reconstruct the sedimentation history of the lake. First results show at least two time frames of extensive and stable lake existence during MIS 3 (44-40 ka cal. BP) and the LGM (21-19 ka cal. BP). Gastropod shell-bearing sediments indicate freshwater to oligohaline conditions.From a geomorphological point of view, our analyses suggest the existences of at least three paleolake phases with unique related drainage systems. However, the morphostratigraphy suggests inferior fluctuations with identifiable sub-phases. [ABSTRACT FROM AUTHOR]

The devastating flood of 1868 in the alps triggered a systematic study of the role of forests for the hydrology in Switzerland (and neighboured countries). As a direct consequence, the first longterm observations of runoff in small forested catchments were launched in 1903 in the Swiss Emmental (and have been run ever since). Several similar longterm investigations of runoff formation in other first-order catchments of the Swiss pre-alps – with different geology, forest compositions and rainfall regimes – followed in the course of the past century, among others the 50-year old hydrological observatory in the Alptal (central Switzerland).Looking back to the history of these old pillars of forest-hydrological research, it becomes obvious that they served much more than for satisfying pure academic curiosity. The legacy of correspondence from the archive tells us that the initiative and planning of new forest-hydrological observatories was closely related with political and forest-promoting interests. In the same way, the results of these studies have been interpreted and communicated in a way that sometimes exceeded pure scientific conclusions. In fact, all these data from more nearly 120 years illustrate a very differentiated (ambiguous) relationship between the presence (and shape) of the forest and the runoff response to heavy rainfall. In contrast, the public doctrine (disseminated by both researchers and stakeholders) was often simplified and biased towards a too positive effect of forests in mitigating floods. On the other hand, the complex (differentiated) insights from numerous specific analyses of students and researchers have often been disremembered.We state that this conclusion doesn't apply only to the present case of forest hydrology, but pose a challenge for other hydrological (or: environmental) topics as well. [ABSTRACT FROM AUTHOR]

Under present day climate change predictions, with both higher magnitude and altered frequencies of flood events, uncertainties exist in how the behaviour of river systems will change in the future. This uncertainty is greater when considering the impact of vegetation on the dynamics of fluvial systems, which itself may also vary because of climate change. Physical modelling can be a valuable tool to understand the processes on a smaller scale, in particular by simulating the effects of vegetation using surrogates that can grow rapidly, thereby mimicking the forcing induced by vegetation growth. Previous studies using surrogate vegetation in flume experiments on braided rivers (e.g. Tal and Paola, 2007; Bertoldi et al., 2015), have shown the potential for this modelling approach. For this research, we allowed braided river systems to evolve under constant conditions in two 2.5 m wide by 10 m long flume channels, set-up in the Total Environments Simulator at the University of Hull. Once equilibrium conditions were reached under bare sediment conditions, Alfalfa was periodically seeded and allowed to germinate and then grow for different time periods. After each period of growth, we used a sequence of high and low magnitude flood events in order to capture change in morphology arising from the different sequences of events. Morphological changes were captured using a terrestrial laser scanner to collect over 50 DEMs. These DEMs demonstrate the impact surrogate vegetation has on both stabilizing the river system and modifying the patterns of bank erosion and channel migration in a braided system. Furthermore, frequent spatial analysis of erosion and deposition based on the flow direction within the channel network allowed us to determine erosion and deposition width for individual segments of the river system. Collating these segments yields a large dataset that indicates both bank erosion rates and volumetric channel migration rates for different stages of vegetation growth/maturity under different sequences of flood events. [ABSTRACT FROM AUTHOR]

The West African Sahel experienced a long drought from the 1970s to the 1990s during which runoff has paradoxically increased, as a response to human and climate-induced changes in surface conditions. Despite the vegetation recovery (re-greening) observed at regional scale over the past 30 years, surface runoff is still increasing, suggesting that the Sahelian eco-hydrological system passed a tipping point and is now trapped in a « high runoff » state. To study this hypothesis, we developed a system dynamics model incorporating vegetation-hydrology interactions at annual time scale. The model successfully reproduced the vegetation collapse and the increase of runoff-prone bare soil areas monitored over 65 years on a pilot site in Northern Mali. Our results confirmed the existence of a tipping point between alternative high/low runoff states at the small catchment scale. According to the model, a reverse shift to the pre-drought low runoff state is possible, but the conditions in which this shift would occur remain uncertain. The system trajectory presents a strong sensitivity to annual rainfall variability (amplitude and temporal structure). This study suggests that the increasing runoff in a re-greening environment is caused by the tipping of some areas to a high runoff/low vegetation state, illustrating how a regime shift in sub-systems can result in eco-hydrological changes at larger scale. The associated large-scale changes of the rainfall partitioning may alter evapo-transpiration and thus the surface-atmosphere feed-back. Those changes also bear strong environmental and socio-economic consequences, either adverse (increase of degraded areas to the detriment of agriculture, and increased flood risk) or beneficial (increased water resource in ponds and water tables). [ABSTRACT FROM AUTHOR]

The SHAPE project is part of SEOM, Scientific Exploitation of Operational Missions, an ESA program element which aims at expanding the international research community, strengthening the leadership of the European EO research community and addressing new scientific researches.This Research and Development intends to make the best use of SAR (delay-Doppler) altimetry data for applications in hydrology. The study focuses on three main variables of interest: river water level (RWL), river discharge (RWD) and lake water level (LWL), RWD and LWL being part of the Terrestrial Essential Climate Variables (TECV) defined by GCOS.The project embraces data processing from L1A altimetry products up to L2 (geophysical products), L3 (water level time series) and L4 (River discharge). It started with CryoSat-2 data (before the launch of Sentinel-3A) and is integrating Sentinel-3A as another input for the SHAPE processor.The project has developed its own modular and configurable altimetric processor comprising a delay-Doppler processor (from L1A to L1b), a L2 processor including state-of-the-art geophysical corrections and new SARM retrackers. On top of this, the SHAPE project also implements its own L3 processor (from L2 to RWL and LWL) and L4 processors (from RWL to RWD) and a validation and verification framework. With the confidence brought by the validation and verification steps, the project implements hydrological dynamic and semi-distributed models of river catchments able to assimilate RWL measurements in order to estimate RWD.The high level of configuration of the processor allows to work in parallel on two different baselines. The first one is dedicated to mimic as much as possible the real Sentinel-3 baseline and the second a baseline optimised for hydrology, at all processing levels.The project focuses on 3 rivers (Amazon, Danube and Brahmaputra) and 2 lakes (Vänern and Titicaca). Sentinel-3A L1A data is considered to be used on the Brahmaputra river while CryoSat-2 L1A data is used on the other water bodies.In this communication, we report both on the achievements made by the project as well as providing results, we also report about its status and planning. [ABSTRACT FROM AUTHOR]

Climate change is very pronounced in high latitudes and impacts permafrost-underlain landscapes with respect to hydrology, ecosystems and the population's traditional livelihoods. However, a strong spatial and temporal variability in temperature and precipitation records renders the characterization of changes as well as the implementation of mitigation strategies difficult. Here we present an approach to investigate temperature and precipitation time series from observational records, reanalysis, and climate model data in the Lena River catchment, Eastern Siberia, Russia, where significant environmental changes are already apparent. We developed a statistical method to identify the time of emergence (ToE) of climate change signals, i.e. the time when a climate signal permanently exceeds its natural variability. Our method provides more freedom than traditional parametric approaches and allows for a detailed temporal analysis of climate signals. The method is based on the Hellinger distance metric to compare probability density functions between a reference and target periods. We use a reference period common to all tested datasets (1900-1921) to provide an estimate for the natural variability, and target periods with moving windows of 21 years thereafter at annual and seasonal scale. We investigate how and when temperature and precipitation signals have emerged from the original value distribution. The metric describes the overlap of the probability density functions (PDFs) of two periods and is adjusted to yield dissimilarities between them as values ranging from 0% to 100%. A strong onset of emergence is apparent in the 1970s for temperature with a monotonic increase thereafter for observational data. The same evolution is obtained for a collection of 65 climate model projections using the RCP85 emission scenario. At the end of the observational dataset (2016), temperature distributions have emerged by 50% to 60%. Climate model projections suggest 90% emergence by 2040. For precipitation the analysis is less conclusive because of high uncertainties in existing observational datasets that also impede an evaluation of the climate model projections. These suggest hardly any emergence by 2000 but a well-defined emergence thereafter, reaching 60% by 2100. An original strategy to select the most realistic model simulations based on the available observational data significantly reduces the uncertainties resulting from the spread in the 65 climate models used. [ABSTRACT FROM AUTHOR]

The incision of rivers into bedrock is considered as one of the most important processesdriving long-term landscape evolution. River incision is non-linearly dependent on riverdischarge, because river discharge must exceed a certain threshold to be able to transportbedload sediment and expose the riverbed to erosion. Fluvial erosion efficiency is, therefore,strongly controlled by the frequency and magnitude of flood events. In this study wehypothesise that catchment attributes, such as regolith thickness, lithology and vegetationcover, modulate the discharge response after a precipitation event, which has implications forthe fluvial erosion efficiency. We present preliminary results from a study, in which we exploit daily discharge recordsfrom 322 river gauging stations on a large climatic gradient in Chile (18˚ S-55˚ S). Thestudied rivers have catchment areas of 15 km2 to 24200 km2, which differ in topography,lithology, regolith thickness, vegetation cover and snow and glacier cover. First, we studieddischarge variability (i.e. magnitude-frequency distribution of flood events) andthe occurrence of different discharge regimes as result of seasonal variations, byobtaining the best fit of a weighted sum of two inverse gamma functions to the data(Scherler et al., 2017). Each of the distributions is interpreted to correspond to oneflow regime. When the weighted sum of two inverse gamma functions performedbetter than one, and each flow regime lasted at least 3 months, we interpret thedifferent flow regimes to reflect seasonal variation in a catchment. Results reveal largevariations in discharge variability along the climate gradient and strong seasonalvariations around 30˚ S-40˚ S which is mainly driven by climatic forcing and snowmelt. We are currently studying discharge variability by obtaining the flood flashinessparameter, the variability index and hydrologic response time from fitting the streamflowrecession model to the daily discharge records (Deal et al., 2018 after Botter et al., 2007). Wewill focus on the differences between seasons and El Niño, La Niña and normalyears and will compare all parameters with calculated topography and datasets ofclimate, vegetation density, regolith thickness, lithology and snow and glacier cover todisentangle their controls on flood flashiness, variability index and hydrologic responsetime. References: Botter, G., Porporato, A., Rodriguez-Iturbe, I. and Rinaldo, A.: Basin-scale soil moisturedynamics and the probabilistic characterization of carrier hydrologic flows: Slow,leaching-prone components of the hydrologic response, Water Resour. Res., 43(2),1–14. Deal, E., Botter, G. and Braun, J.: Understanding the role of rainfall and hydrology indetermining fluvial erosion efficiency, J. Geophys. Res. Earth Surf., 2018. Scherler, D., DiBiase, R. A., Fisher, G. B. and Avouac, J. P.: Testing monsoonal controlson bedrock river incision in the Himalaya and Eastern Tibet with a stochastic-thresholdstream power model, J. Geophys. Res. Earth Surf., 122(7), 1389–1429, 2017. [ABSTRACT FROM AUTHOR]

Sediment dynamics in river catchments are governed by tectonics, climate and biota. They act directly on the transport process by controlling topography and sediment transport capacity (runoff) and indirectly by controlling the flux and grain size distribution (GSD) of sediments supplied from hillslopes to the fluvial system. Since climate is the main driver for biotic activity, both effects are strongly coupled, and often difficult to disentangle. However, while climate forcing shows a clear trajectory towards increased erosion with increasing humidity, the effect of vegetation is more ambiguous. On short timescales vegetation reduces hillslope erosion and sediment supply from hillslopes by stabilizing soils and trapping sediments. On longer timescales an increased sediment residence time and enhanced biochemical weathering of material in the soils enhances the production fine grained material and hence strongly alters the GSD of material delivered to the fluvial transport system. We state that the influence of vegetation on the grain size distribution of sediments supplied to the river system is a key factor in the biotic control on sediment dynamics, since it exerts a strong control on the transport mechanics and morphodynamics in the river system which in turn control incision and deposition and hence landscape evolution. To investigate vegetation induced shifts in GSD, we collected grain size samples of hillslope and channel sediments in four granitic mountainous river catchments located along the strong bioclimatic gradient of the Chilean Coastal Cordillera, ranging from the arid, non-vegetated Atacama desert in the north (26°S) to the humid and densely vegetated Cordillera Nahuelbuta in the south (38°S). 78 volumetric bulk samples were taken with grain sizes ranging from clay (d = 0.3μm) to boulders (d >300mm). By sampling hillslope and fluvial sediments from the hilltop to the channel outlet we track the effect of vegetation on the spatial variability of GSDs along the sediment transport path.Results show that hillslope sediments in humid areas contain higher fraction of fines compared to the arid areas, while channel sediments in contrast are much coarser. Uniform GSDs in the arid catchments reflect nonselective and thus transport-limited conditions in the river channels. In contrast, in humid catchments GSDs show strong differences between fine hillslope sediment and coarse channel deposits, indicating size selective and supply-limited transport conditions in catchment with higher vegetation coverage. [ABSTRACT FROM AUTHOR]

Geology is a main pattern of catchment organization, and we ask whether it impacts the hydrological response of catchments, especially during floods. The aim of our study is to assess which hydrological processes are linked to the geological pattern, and to which extend the latter can affect water balance and runoff coefficient at catchment scale. For that, we propose to compare the main components of the water balance to geomorphological indicators, in order to assess the potential transferability of results to ungauged catchments. Our method consists in a complete water budget assessment of catchments at their outlet, including precipitations P, evapotranspiration E, runoff Q, and intercatchment groundwater flows (IGF), combined to a geomorphological and geological characterisation. Data are based on the annual components of the water balance, calculated from pluri-annual time series at a daily time step for medium catchments (from 50 to 500 km²). For each outlet, are differentiated global and intermediate catchments (defined as the draining area that feeds a river reach delimited by two gauging stations). The whole study site (total of 25 000 km²) is composed by 3 zones of various geology in France (Cévennes Mountains, Jura Mountains, Normandy) including 120 gauging stations. In a first step, results show that many catchments have a "non conservative" water balance (i.e. Q > P or Qupstream > Qdownstream), and that this behaviour can be linked to the catchment geology (differentiating hard-rock, karst, and other sedimentary formations). Results also show that both quick and slow flow components (deduced from hydrograph separation) are correlated with geology, as well as the IGFs. The impact of land use is also studied, and compared with geology. In a second step, we characterize relationships between those hydrological specificities and some simple geomorphological parameters, i.e. drainage density and IDPR (Index of Development and Persistency of River networks, quantifying the terrains connectivity to hydrographic network). Results show that correlations exist, relatively strong depending on the study sites and geology. The case of karst areas – that characterize carbonate outcrops – is highlighted due to the highest variability of hydrological indicators in catchments covers by such patterns. A parallel review of the local artificial tracing tests shows that the weakness of the correlations in the karst Jura Mountains could be explained by the importance of IGFs that are highly promoted in these regions. Finally, our results highlight the geological control of catchment hydrology and the specific role of groundwater flows in karst areas on flood flows. Knowing that karst areas cover 20% of Europe outcrops, this work promises interesting perspective in mapping hydrological indicators in link with catchment organization and geology. [ABSTRACT FROM AUTHOR]

PCR-GLOBWB (https://github.com/UU-Hydro/PCR-GLOBWB%5fmodel) is a global hydrology and water resources model being developed over the past two decades at the Department of Physical Geography, Utrecht University, The Netherlands. The latest version of the model has a spatial resolution of 5 arcmin (less than 10 km at the equator), covering all continents except Greenland and Antarctica, and runs with daily time-steps. The model includes a two-layer MODFLOW model to simulate lateral groundwater flow for assessing global scale groundwater dynamics, including regions with declining groundwater heads due to overexploitation.Within the hydrologic scientific community there is a strong need for hyper-resolution global hydrological modelling, requiring spatial resolutions ranging from 100 m to 1 km (http://www.hyperhydro.org/). It is expected that such models will aid scientists in making advances in modelling, e.g., regarding global biogeochemical cycling, along-river sediment transport, global flood hazard and risk, and process understanding within catchments. Another reason, yet technology pushed, for pursuing hyper-resolutions models is that our current post-petascale and next-generation exascale supercomputers, having thousands to millions of computational cores, should make such models possible. However, from a computer science point of view, realising such models is a far from trivial task, since this involves big data handling and solving a huge system with millions to billions of cells, where highly efficient parallel algorithms and numerical methods are pre-requisite.In this work, some first promising results are presented for the two-layer global scale MODFLOW model consisting of more than 250 million active cells having 30 arcsec resolution (less than 1 km resolution). We consider a steady-state groundwater model only and our results focus on the numerical challenge to solve this model in parallel. For this, parallel MODFLOW 6 is used that is being developed together with the United States Geological Survey. This code includes an additive Schwarz parallel preconditioner and uses the Message Passing Interface (MPI) to couple the submodels. A sub-optimal load-balancing partition method is evaluated where the computational grid is initially partitioned into a large number of subdomains, where one or more subdomains exactly form a surface water catchment area. The resulting MODFLOW (multi-)model is kept fixed and for each parallel run one or more submodels are uniquely assigned to a processor core (MPI rank). Motivations for doing this are: a) to meet the hydrologist who models at catchment level, b) to reduce error checking to a single model, c) to save pre-processing time which can be large for highly transient input data, d) to simplify future parallel coupling of the MODFLOW model to the PCR-GLOBWB land surface and surface water routing modules. All experiments are carried out on the Dutch national supercomputer Cartesius using up to 1000 computational cores. [ABSTRACT FROM AUTHOR]