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Identifying a ‘best’ performing hydrologic model in a practical sense is difficult due to the potential influences of modeller subjectivity on, for example, calibration procedure and parameter selection. This is especially true for model applications at the event scale where the prevailing catchment conditions can have a strong impact on apparent model performance and suitability. In this study, two lumped models (CoupModel and HBV) and two physically-based distributed models (LISEM and MIKE SHE) were applied to a small catchment upstream of a road in south-eastern Norway. All models were calibrated to a single event representing typical winter conditions in the region and then applied to various other winter events to investigate the potential impact of calibration period and methodology on model performance. Peak flow and event-based hydrographs were simulated differently by all models leading to differences in apparent model performance under this application. In this case-study, the lumped models appeared to be better suited for hydrological events that differed from the calibration event (i.e., events when runoff was generated from rain on non-frozen soils rather than from rain and snowmelt on frozen soil) while the more physical-based approaches appeared better suited during snowmelt and frozen soil conditions more consistent with the event-specific calibration. This was due to the combination of variations in subsurface conditions over the eight events considered, the subsequent ability of the models to represent the impact of the conditions (particularly when subsurface conditions varied greatly from the calibration event), and the different approaches adopted to calibrate the models. These results indicate that hydrologic models may not only need to be selected on a case-by-case basis but also have their performance evaluated on an application-by-application basis since how a model is applied can be equally important as inherent model structure. [ABSTRACT FROM AUTHOR]

Abstract: A physically-based, distributed hydrological model (MIKE SHE) was used to quantify overland runoff in response to four extreme rain events and four types of simulated land use measure in a catchment in Norway. The current land use in the catchment comprises arable lands, forest, urban areas and a stream that passes under a motorway at the catchment outlet. This model simulation study demonstrates how the composition and configuration of land use measures affect discharge at the catchment outlet differently in response to storms of different sizes. For example, clear-cutting on 30% of the catchment area produced a 60% increase in peak discharge and a 10% increase in total runoff resulting from a 50-year storm event in summer, but the effects on peak discharge were less pronounced during smaller storms. Reforestation of 60% of the catchment area was the most effective measure in reducing peak flows for smaller (2-, 5- and 10-year) storms. Introducing grassed waterways reduced water velocity in the stream and resulted in a 28% reduction in peak flow at the catchment outlet for the 50-year storm event. Overall, the results indicate that the specific effect of land use measures on catchment discharge depends on their spatial distribution and on the size and timing of storm events. [Copyright &y& Elsevier]

Summary: Permafrost, mainly of discontinuous type, that underlies the tundra and taiga landscapes of the Nadym and Pur river basins in northwestern Siberia has been warming during the recent decades. A mosaic of thermokarst lakes and wetlands dominates this area. In this study we tested the hypothesis chain that permafrost thawing changes thermokarst lake area and number, and is then also reflected in and detectable through other associated hydrological changes. Based on indications from previous studies, the other hydrological changes in a basin were expected to be decreasing intra-annual runoff variability (quantified by decreasing maximum and increasing minimum runoff) and systematically decreasing water storage. To test this hypothesis chain, we mapped thermokarst lake changes using remote sensing analysis and analyzed both climate (temperature and precipitation) and water flow and balance changes using available monthly data records. This was done for the whole Nadym and Pur river basins and a smaller sub-basin of the former (denoted 7129) with comparable data availability as the whole river basins. The results for the 7129 sub-basin show all the indicators (thermokarst lake and other hydrological) changing consistently, as could be expected in response to permafrost thawing that alters the connections between surface and subsurface waters, and leads to overall decreases in water (including ground ice) storage within a basin. Over the Nadym and Pur basins, the relative area influenced by similar permafrost thawing and associated lake and hydrological effects appears (yet) too small to be clearly and systematically reflected in the basin-average indicators for these large basins. [ABSTRACT FROM AUTHOR]

Abstract: In humid, well-vegetated areas, such as in the northeastern US, runoff is most commonly generated from relatively small portions of the landscape becoming completely saturated, however, little is known about the spatial and temporal behavior of these saturated regions. Indicator kriging provides a way to use traditional water table data to quantify probability of saturation to evaluate predicted spatial distributions of runoff generation risk, especially for the new generation of water quality models incorporating saturation excess runoff theory. When spatial measurements of a variable are transformed to binary indicators (i.e., 1 if above a given threshold value and 0 if below) and the resulting indicator semivariogram is modeled, indicator kriging produces the probability of the measured variable to exceed the threshold value. Indicator kriging gives quantified probability of saturation or, consistent with saturation excess runoff theory, runoff generation risk with depth to water table as the variable and the threshold set near the soil surface. The probability of saturation for a 120m×180m hillslope based upon 43 measurements of depth to water table is investigated with indicator semivariograms for six storm events. The indicator semivariograms show high spatial structure in saturated regions with large antecedent rainfall conditions. The temporal structure of the data is used to generate interpolated (soft) data to supplement measured (hard) data. This improved the spatial structure of the indicator semivariograms for lower antecedent rainfall conditions. Probability of saturation was evaluated through indicator kriging incorporating soft data showing, based on this preliminary study, highly connected regions of saturation as expected for the wet season (April through May) in the Catskill Mountain region of New York State. Supplementation of hard data with soft data incorporates physical hydrology of the hillslope to capture significant patterns not available when using hard data alone for indicator kriging. With the need for water quality models incorporating appropriate runoff generation risk estimates on the rise, this manner of data will lay the groundwork for future model evaluation and development. [Copyright &y& Elsevier]

Tile outlet discharge, soil moisture, and groundwater response were monitored for one year from a 10-ha catchment in north-central Ohio to understand the impact of automated drainage water management (ADWM) following 16 storm events. Under ADWM the tile outlet valve was programmed to open and release water when the water level in the control structure reached a user defined set point below the soil surface. Average groundwater level, soil moisture, and percentage of surface flooding indicated by groundwater levels were not significantly different following precipitation events during periods of ADWM compared to free drainage. However, the time to achieve maximum soil water moisture following precipitation onset was significantly longer and lateral hydraulic gradients were greater during periods of free drainage compared to periods of ADWM, which potentially alters how agricultural fields contribute water through edge-of-field buffers and waterways. In addition, maximum discharge occurred significantly later for storm events that occurred during ADWM; however, total tile outlet discharge was surprisingly not significantly different for events that happened under ADWM compared to events that occurred during free drainage. Tile outlet discharge for precipitation events occurring under ADWM was significantly correlated with the percentage of time during the event in which the tile outlet valve was opened. ADWM for this study was thus more effective at retaining water in the field and reducing tile outlet to near zero discharge during low-intensity precipitation events and when dry antecedent conditions were present. Our results highlight that fields under ADWM are not isolated from the surrounding landscape as they still allow water to move beyond the boundary of the field through combinations of (1) redistributions or reconnections of subsurface flow pathways and (2) periodic opening of outlet valves to release tile drainage water during large storm events and wet conditions. • Maximum groundwater and soil moisture after storms were not significantly different during free drainage compared to ADWM • Hydraulic gradients were significantly greater during times of free drainage compared to automated drainage water management • After storms, tile outlet discharge was not significantly different during free drainage conditions compared to ADWM • Automated drainage water management delayed the time to peak tile outlet discharge compared to free drainage [ABSTRACT FROM AUTHOR]

Abstract: Road drainage structures are often designed using methods that do not consider process-based representations of a landscape's hydrological response. This may create inadequately sized structures as coupled land cover and climate changes can lead to an amplified hydrological response. This study aims to quantify potential increases of runoff in response to future extreme rain events in a 61km2 catchment (40% forested) in southwest Sweden using a physically-based hydrological modelling approach. We simulate peak discharge and water level (stage) at two types of pipe bridges and one culvert, both of which are commonly used at Swedish road/stream intersections, under combined forest clear-cutting and future climate scenarios for 2050 and 2100. The frequency of changes in peak flow and water level varies with time (seasonality) and storm size. These changes indicate that the magnitude of peak flow and the runoff response are highly correlated to season rather than storm size. In all scenarios considered, the dimensions of the current culvert are insufficient to handle the increase in water level estimated using a physically-based modelling approach. It also appears that the water level at the pipe bridges changes differently depending on the size and timing of the storm events. The findings of the present study and the approach put forward should be considered when planning investigations on and maintenance for areas at risk of high water flows. In addition, the research highlights the utility of physically-based hydrological models to identify the appropriateness of road drainage structure dimensioning. [Copyright &y& Elsevier]

Summary: During the 20th century, Sweden underwent a persistent agricultural development. In this study, we use and combine historical hydroclimatic and agricultural data to investigate how this large scale change of land use, and subsequent intensification of crop production, affected regional hydrology in two adjacent Swedish drainage basins. We find a main increase of evapotranspiration (ET) as cultivated area and/or crop production increased during the period 1901–1940. Thereafter, ET stabilized at a new higher level. Comparison between the data given, water balance constrained ET quantification (ETwb), and a range of different comparative estimates of purely climate driven ET (ETclim) shows that only 31% of the steep 1901–1940 increase of ETwb can be explained by climate change alone. The remaining 69% of this ETwb shift, which occurred in both investigated drainage basins, is instead explainable to large degree by the regional land use conversion from seminatural grasslands to cultivated land and associated enhanced productivity of herbaceous species. [Copyright &y& Elsevier]

Specialty crop production requires large volumes of water for irrigation and faces four interconnected water resource concerns: (1) water availability and security, (2) need for high water quality (3) management of irrigation return flow (IRF) and operational water (OW) quality from production areas, and (4) increasing consumer and regulatory pressure to mitigate non-point source runoff. Retention reservoirs (RRs) are an effective best management practice for extending water resources and reducing an adverse effect on the environment. RRs are recommended for specialty crop producers to (1) capture stormwater and OW to conserve increasingly limited and costly water resources, (2) reduce reliance on surface- and ground-water, and (3) mitigate contaminants in OW before discharge into receiving waters. Despite the importance of RRs for water security, concerns remain about their capacity to mitigate contaminants prior to use of captured IRF and stormwater. Specialty crop producers perceive potential risks of reapplying contaminants to economically important crops. Consolidated information is needed on the risks associated with IRF and stormwater reuse, design of RRs for adequate storage for capturing both IRF and stormwater, and the effects of RRs on operational and discharged water quality. The main goals of this critical assessment were to (1) understand the effect of RRs on contaminant mitigation; (2) collate information about quality of water in RRs reused for irrigation; and (3) develop guidelines for designing RRs used in specialty crop production. Proper design or augmentation of new and existing water RRs can enable specialty crop producers to collect, reuse, or discharge freshwater that meets quality metrics. Three RR design methods were compared. Current RRs design recommendations to capture a 24-h rainfall with 25-year frequency may be inadequate to capture OW or a portion of rainfall for many parts of the USA. Modifying RR design specifications to capture a 24-h rainfall with 50-year frequency will increase operational climate resilience, water security, and reduce non-point source runoff. Additionally, use of a forebay, increasing depth, long flow path (high length/width ratio), long hydraulic retention time, and aeration or mixing are discussed to optimize water treatment within RRs. • Role of specialty crop retention reservoir (RR) for cleaner production reviewed. • RR water quality irrigation reuse data for collated for several US locations. • Three RR design methods were defined, developed, and compared. • RR design specifications should capture 24-h rainfall with 50-year frequency. • Best practices discussed for RR design to optimize water treatment. [ABSTRACT FROM AUTHOR]

Abstract There is an urgent need to develop agricultural methods that balance water supply and demand while at the same time improve resilience to climate variability. A promising instrument to address this need is biochar – a charcoal made from pyrolyzed organic material. However, it is often unclear how, if at all, biochar improves soil water availability, plant water consumption rates and crop yields. To address this question, we synthesized literature-derived observational data and evaluated the effects of biochar on evapotranspiration using a minimal soil water balance model. Results from the model were interpreted in the Budyko framework to assess how climatic conditions mediate the impacts of biochar on water fluxes. Our analysis of literature-derived observational data showed that while biochar addition generally increases the soil water holding capacity, it can have variable impacts on soil water retention relative to control conditions. Our modelling demonstrated that biochar increases long-term evapotranspiration rates, and therefore plant water availability, by increasing soil water retention capacity – especially in water-limited regions. Biochar amendments generally increased crop yields (75% of the compiled studies) and, in several cases (35% of the compiled studies), biochar amendments simultaneously increased crop yield and water use efficiencies. Hence, while biochar amendments are promising, the potential for variable impact highlights the need for targeted research on how biochar affects the soil-plant-water cycle. Graphical abstract Unlabelled Image Highlights • Data synthesis shows biochar generally increases soil water retention capacity. • In some cases, biochar improved both crop yields and water use efficiencies. • Modelling found biochar to consistently increase ET rates, mainly in water limited regions. • Biochar may boost agricultural yield and resilience to variability of rainfall. • Theory-practice gap of biochar effects on soil water: integrative research needed. [ABSTRACT FROM AUTHOR]

Wetlands are often considered as nature-based solutions that can provide a multitude of services of great social, economic and environmental value to humankind. Changes in land-use, water-use and climate can all impact wetland functions and services. These changes occur at scales extending well beyond the local scale of an individual wetland. However, in practical applications, engineering and management decisions usually focus on individual wetland projects and local site conditions. Here, we systematically investigate if and to what extent research has addressed the large-scale dynamics of landscape systems with multiple wetlands, hereafter referred to as wetlandscapes, which are likely to be relevant for understanding impacts of regional to global change. Although knowledge in many cases is still limited, evidence suggests that the aggregated effects of multiple wetlands in the landscape can differ considerably from the functions observed at individual wetland scales. This applies to provisioning of ecosystem services such as coastal protection, biodiversity support, groundwater level and soil moisture regulation, flood regulation and contaminant retention. We show that parallel and circular flow-paths, through which wetlands are interconnected in the landscape, may largely control such scale-function differences. We suggest ways forward for addressing the mismatch between the scales at which changes take place and the scale at which observations and implementation are currently made. These suggestions can help bridge gaps between researchers and engineers, which is critical for improving wetland function-effect predictability and management. [ABSTRACT FROM AUTHOR]