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Summary: There is increasing concern about the availability of water supplies in developing countries to provide clean drinking water and sanitation as well as providing for irrigation for food security. This has led to hydrologically led investigation to establish the feasibility and storage capacity of potentially new dam sites. This task has become more difficult for hydrologists and others with the uncertainties created by climate change and the measurement of the hydrological, geographical and ecological footprint of new dams. The questions asked by hydrologists are increasingly likely to be required to be cast in terms of the four pillars of sustainability; environmental, economic, social and institutional. Similarly, regional planners have to be more cognisant of the social outcomes of dam development while understanding the wider hydrological context at a watershed and basin level. The paper defines the concept of sustainability assessment in the context of resettlement and analyses its implications for the Bakun Hydro-electric project in Sarawak, Malaysia. Specifically it attempts to address the question of what social sustainability would really mean in the context of communities affected by dam projects, and their catchments using hermeneutics, tradeoffs and offsets. The findings of this question were presented at a hydrological conference held in Santiago in October 2010, based on the outcome of specific questionnaire responses received from indigenous peoples affected by the Bakun Dam hydroelectric project. The paper also offers some insights pertaining to the social sustainability assessment aspects of dams and their catchments. [ABSTRACT FROM AUTHOR]

Summary: Abundant information is available on West African drought and its hydrological and environmental impacts. Land-use and climatic changes have greatly modified the conditions of Sudanian and Sahelian hydrology, impacting the regime and discharge of the main rivers. Human pressure on the environment (significant increase in crops and disappearance of natural bushes and landscapes, for example) has led to severe soil crusting and desertification throughout Sahelian regions. Despite recent increases in rainfall, the drought has not ended, resulting in two different hydrological evolutions. In the Sudanian areas, stream flows have been reduced, sometimes as much as twice the rainfall reduction rate. In the Sahelian regions, runoff coefficients have increased to such a degree that discharges are increasing, in spite of the reduced rainfall. The main goal of this paper is to synthesize the recent advances in the Sahelian and Sudano-Sahelian West African hydrology. The other objectives are two fold: First, to discuss the “Sahelian Paradox” (the increase in runoff in most of the Sahel during the drought, at least during the 1968–1995 period, as described in the 1980s) and paradox of groundwater highlighted in the square degree of Niamey (the rise in water table levels in some endorheic areas during the same drought, evidenced in the 1990s), and second, to attempt to define the application of their respective geographical areas. The land-use changes act as a general factor of hydrological evolution of soils and basins, while some spatial factors explain the great variability in the response to environmental evolution, such as endorheism, geological context, latitudinal climate gradient, and local hydrodynamic behaviour of environment. This paper is literature-based, and incorporates current research advances in the field, as well as a prospective focused on resources and socio-economic impacts. [Copyright &y& Elsevier]

The assessment for impacts of climate variability and human activities on suspended sediment yield (SSY) change has long been a question of great interest. However, the sediment generation processes are sophisticated with high nonlinearity and great uncertainty, which give rise to extreme complexity for SSY change assessment in Newtonian approach. Consequently, few approaches can be simply but widely applied to decompose impacts of climatic variability and human activities on SSY change. Thus, it is an urgent need to develop advanced methods that are simple and robust. Since that the Newtonian approach is hardly achievable due to limitation of either observations or knowledge of mechanisms, there have been repeated calls to capture the hydrologic system in Darwinian approach for hydrological change prediction or explanation. As streamflow is the carrier of suspended sediment, SSY change are thus documented in changes of sediment concentrated flow and suspended sediment concentration – water discharge ( C - Q ) relationships. By deduced corollaries, a differential equation of sediment discharge change was derived to explicitly decompose impacts of climate variability and human activities in Darwinian hydrology. Besides, a new form of sediment rating curves was proposed and curved as C - Q relationships and probability distribution of sediment concentrated flow. River sediment flux can be revealed by this representation, which simply elucidates mechanism of SSY generation covering a range of time scales from finer than rainfall-event to long term. By the new sediment rating curves, the differential equation was partly solved using a segmentation algorithm proposed and validated in this paper, and then was submitted to water balance framework expressed by Budyko-type equation. Thus, for catchment management, hydrologists can obtain explicit explanation of how climate variation and human activities propagate through landscape and result in sediment discharge change. The differential equation is simple and robust for widely application in sediment discharge change assessment, as only discrete data of precipitation, potential evaporation and C - Q observed at gauging stations are required. [ABSTRACT FROM AUTHOR]

Watershed management (WSM) is the most widely adopted technology in developed as well as developing countries due to its suitability across climatic conditions. Watershed technology is suitable to protect and enhance soil fertility, which is deteriorating at an alarming rate with agricultural intensification in high as well as low rainfall regions. Of late, WSM is considered as an effective poverty alleviation intervention in the rain fed regions in countries like India. This paper aims at providing a basic watershed policy and implementation framework based on a critical review of experiences of WSM initiatives across South Asia. The purpose is to provide cross learnings within South Asia and other developing countries (especially Africa) that are embarking on WSM in recent years. Countries in the region accord differential policy priority and are at different levels of institutional arrangements for implementing WSM programmes. The implementation of watershed interventions is neither scientific nor comprehensive in all the countries limiting the effectiveness (impacts). Implementation of the programmes for enhancing the livelihoods of the communities need to strengthen both technical and institutional aspects. While countries like India and Nepal are yet to strengthen the technical aspects in terms of integrating hydrogeology and biophysical aspects into watershed design, others need to look at these aspects as they move towards strengthening the watershed institutions. Another important challenge in all the countries is regarding the distribution of benefits. Due to the existing property rights in land and water resources coupled with the agrarian structure and uneven distribution and geometry of aquifers access to sub-surface water resources is unevenly distributed across households. Though most of the countries are moving towards incorporating livelihoods components in order to ensure benefits to all sections of the community, not much is done in terms of addressing the equity aspects of WSM. [ABSTRACT FROM AUTHOR]

Recently developed methodologies such as climate reanalysis make it possible to create a historical record of climate systems. This paper proposes a methodology called Hydrological Retrospective (HR), which essentially simulates large rainfall datasets, using this as input into hydrological models to develop a record of past hydrology, making it possible to analyze past floods and droughts. We developed a methodology for the Amazon basin, where studies have shown an increase in the intensity and frequency of hydrological extreme events in recent decades. We used eight large precipitation datasets (more than 30 years) as input for a large scale hydrological and hydrodynamic model (MGB-IPH). HR products were then validated against several in situ discharge gauges controlling the main Amazon sub-basins, focusing on maximum and minimum events. For the most accurate HR, based on performance metrics, we performed a forecast skill of HR to detect floods and droughts, comparing the results with in-situ observations. A statistical temporal series trend was performed for intensity of seasonal floods and droughts in the entire Amazon basin. Results indicate that HR could represent most past extreme events well, compared with in-situ observed data, and was consistent with many events reported in literature. Because of their flow duration, some minor regional events were not reported in literature but were captured by HR. To represent past regional hydrology and seasonal hydrological extreme events, we believe it is feasible to use some large precipitation datasets such as i) climate reanalysis, which is mainly based on a land surface component, and ii) datasets based on merged products. A significant upward trend in intensity was seen in maximum annual discharge (related to floods) in western and northwestern regions and for minimum annual discharge (related to droughts) in south and central-south regions of the Amazon basin. Because of the global coverage of rainfall datasets, this methodology can be transferred to other regions for better estimation of future hydrological behavior and its impact on society. [ABSTRACT FROM AUTHOR]

In this paper we present the results of the development and calibration of a fine-scaled quasi-2D hydrodynamic model (IWRM-LXQ) for the Long Xuyen Quadrangle – an important interprovincial agricultural region in the Vietnamese Mekong Delta. We use the Long Xuyen Quadrangle as a case study to highlight the need for further investment in hydrodynamic modelling at scales relevant to the decisions facing water resource managers and planners in the Vietnamese Mekong Delta. The IWRM-LXQ was calibrated using existing data from a low flood year (2010) and high flood year (2011), including dry season and wet season flows. The model performed well in simulating low flood and high flood events in both dry and wet seasons where good spatial and temporal data exists. However, our study shows that there are data quality issues and key data gaps that need to be addressed before the model can be further refined, validated and then used for decision making. The development of the IWRM-LXQ is timely, as significant investments in land and water resource development and infrastructure are in planning for the Vietnamese Mekong Delta. In order to define the scope of such investments and their feasibility, models such as the IWRM-LXQ are an essential tool to provide objective assessment of investment options and build stakeholder consensus around potentially contentious development decisions. [ABSTRACT FROM AUTHOR]

Summary The assessment of climate change impacts on hydrology is subject to uncertainties related to the climate change scenarios, stochastic uncertainties of the hydrological model and structural uncertainties of the hydrological model. This paper focuses on the contribution of structural uncertainty of hydrological models to the overall uncertainty of the climate change impact assessment. To quantify the structural uncertainty of hydrological models, four physically based hydrological models (SWAT, PRMS and a semi- and fully distributed version of the WetSpa model) are set up for a catchment in Belgium. Each model is calibrated using four different objective functions. Three climate change scenarios with a high, mean and low hydrological impact are statistically perturbed from a large ensemble of climate change scenarios and are used to force the hydrological models. This methodology allows assessing and comparing the uncertainty introduced by the climate change scenarios with the uncertainty introduced by the hydrological model structure. Results show that the hydrological model structure introduces a large uncertainty on both the average monthly discharge and the extreme peak and low flow predictions under the climate change scenarios. For the low impact climate change scenario, the uncertainty range of the mean monthly runoff is comparable to the range of these runoff values in the reference period. However, for the mean and high impact scenarios, this range is significantly larger. The uncertainty introduced by the climate change scenarios is larger than the uncertainty due to the hydrological model structure for the low and mean hydrological impact scenarios, but the reverse is true for the high impact climate change scenario. The mean and high impact scenarios project increasing peak discharges, while the low impact scenario projects increasing peak discharges only for peak events with return periods larger than 1.6 years. All models suggest for all scenarios a decrease of the lowest flows, except for the SWAT model with the mean hydrological impact climate change scenario. The results of this study indicate that besides the uncertainty introduced by the climate change scenarios also the hydrological model structure uncertainty should be taken into account in the assessment of climate change impacts on hydrology. To make it more straightforward and transparent to include model structural uncertainty in hydrological impact studies, there is a need for hydrological modelling tools that allow flexible structures and methods to validate model structures in their ability to assess impacts under unobserved future climatic conditions. [ABSTRACT FROM AUTHOR]

Summary This paper investigates patterns of lake-area and hydro-climatic change in Arctic river basins, and possible influence of permafrost change reflected in such patterns. A salient change pattern, emerging across all investigated basins in both permafrost and non-permafrost areas, is an opposite change direction in runoff ( R ) from that in precipitation ( P ). To explain this change contrast, an increase (decrease) in relative water-balance constrained evapotranspiration ET wb / P is required where R decreases (increases). Increasing temporal variability of daily river discharge ( sdQ ) is found in all basins with spatially extensive lake decrease, which also exhibit decrease in ET wb / P . Clear indication of basin-wide permafrost thaw is found in only one basin, and is possible in two more, but unlikely in the largest of the total four investigated permafrost basins. [ABSTRACT FROM AUTHOR]

Summary Areal reduction factors (ARFs) are commonly used to transform point design rainfall to represent the average design rainfall for a catchment area. While there has been considerable attention paid in the research and engineering communities to the likely changes in rainfall intensity in future climates, the issue of changes to design areal rainfall has been largely ignored. This paper investigates the impact of climate change on ARFs. A new methodology for estimating changes in ARFs is presented. This method is used to assess changes in ARFs in the greater Sydney region using a high-resolution regional climate model (RCM). ARFs under present (1990–2009) and future (2040–2059) climate conditions were derived and compared for annual exceedance probabilities (AEPs) from 50% to 5% for durations ranging from 1 h to 120 h. The analysis shows two main trends in the future changes in ARFs. For the shortest duration events (1-h) the ARFs are found to increase which implies that these events will tend to have a larger spatial structure in the future than the current climate. In contrast, storms with durations between 6 and 72 h are likely to have decreased ARFs in the future, suggesting a more restricted spatial coverage of storms under a warming climate. The extent of the decrease varies with event frequency and catchment size. The largest decreases are found for large catchments and rare events. Although the results here are based on a single RCM and need to be confirmed in future work with multiple models, the framework that is proposed will be useful for future studies considering changes in the areal extent of rainfall extremes. [ABSTRACT FROM AUTHOR]

Summary Evapotranspiration (ET) is a key variable for hydrologic, climatic and agricultural studies. ET cannot be measured in many situations and its estimation is only possible through the application of mathematical models. ET is commonly calculated relying on reference evapotranspiration (ET o ) or potential evapotranspiration (PET). In particular, temperature-based models (TET) are interesting, because temperature is a widely available climatic variable and it might explain a significant fraction of ET o and PET variability. Nevertheless, most studies about TET models usually provide a local assessment of the studied model performance, usually at regional or national scale. This paper presents the assessment of 11 representative TET methods for estimating ET o and PET considering a very wide climatic spectrum, specifically 4362 climatological stations worldwide. Therefore, the applicability of the different TET approaches was evaluated in relationship to the Köppen climate classification of the stations, considering a monthly timescale and FAO56 Penman Monteith benchmarks (PM56). The encountered correlation indexes confirm the importance of air temperature for modeling ET. In general, the Hargreaves–Samani equation provided the most accurate global average performance in arid, semiarid, temperate, cold and polar climates. The Thornthwaite and McCloud approaches provide the worst average estimates in all climate classes. TET approaches yield high errors and a low average correlation to PM56 in tropical climates. Although a similar comparative analysis might provide other trends at local scale, the presented results might allow for a general selection of suitable TET methods for each climate Köppen class. [ABSTRACT FROM AUTHOR]

Summary Return period and risk of extreme hydrological events are critical considerations in water resources management. The stationarity assumption of extreme events for conducting hydrological frequency analysis to estimate return period and risk is now problematic due to climate change. Two different interpretations of return period, i.e. the expected waiting time (EWT) and expected number of exceedances (ENE), have already been proposed in literature to consider nonstationarity in return period and risk analysis by introducing the time-varying moment method into frequency analysis, under the assumption that the statistical parameters are functions only of time. This paper aimed at improving the characterization of nonstationary return period and risk under the ENE interpretation by employing meteorological covariates in the nonstationary frequency analysis. The advantage of the method is that the downscaled meteorological variables from the General Circulation Models (GCMs) can be used to calculate the nonstationary statistical parameters and exceedance probabilities for future years and thus the corresponding return period and risk. The traditional approach using time as the only covariate under both the EWT and ENE interpretations was also applied for comparison. Both approaches were applied to annual minimum monthly streamflow series of two stations in the Wei River, China, and gave estimates of nonstationary return period and risk that were significantly different from the stationary case. The nonstationary return period and risk under the ENE interpretation using meteorological covariates were found more reasonable and advisable than those of the EWT and ENE cases using time alone as covariate. It is concluded that return period and risk analysis of nonstationary low-flow series can be helpful to water resources management during dry seasons exacerbated by climate change. [ABSTRACT FROM AUTHOR]

Summary Many hydro-climatological applications require use of General Circulation Models (GCMs) outputs. However, the raw information as available from GCMs often contains significant systematic biases when compared with observations. This necessitates some kind of statistical adjustment to be carried out on the GCM fields before their use in any application. It is common to correct the GCM simulations by removing the systematic biases at the time scale of interest, usually individually for each GCM variable that is needed. The outcome is a set of bias corrected variables that are not assessed for bias in their joint dependence structure, nor biases in all attributes at other time scales (such as daily and monthly and annual) except the one under consideration. In this paper, we present a bias correction approach that simultaneously adjusts for the biases in multiple variables across multiple time scales. The proposed Multivariate Recursive Nesting Bias Correction (MRNBC) approach simultaneously corrects many GCM variables and repeats the procedure across different levels of temporal aggregation to impart observed distributional and persistence properties at multiple time scales. The bias corrected series exhibits improvements across all variables and over all the time scales considered. The use of the approach in hydrology and water resources related downscaling applications is expected to deliver better results. [ABSTRACT FROM AUTHOR]

Summary Glacier shrinkage caused by climate change is likely to trigger diminished and less consistent stream flow in glacier-fed watersheds worldwide. To understand, model, and adapt to these climate-glacier-water changes, it is vital to integrate the analysis of both water availability (the domain of hydrologists) and water use (the focus for social scientists). Drawn from a case study of the Santa River watershed below Peru’s glaciated Cordillera Blanca mountain range, this paper provides a holistic hydro-social framework that identifies five major human variables critical to hydrological modeling because these forces have profoundly influenced water use over the last 60 years: (1) political agendas and economic development; (2) governance: laws and institutions; (3) technology and engineering; (4) land and resource use; and (5) societal responses. Notable shifts in Santa River water use—including major expansions in hydroelectricity generation, large-scale irrigation projects, and other land and resource-use practices—did not necessarily stem from changing glacier runoff or hydrologic shifts, but rather from these human variables. Ultimately, then, water usage is not predictable based on water availability alone. Glacier runoff conforms to certain expected trends predicted by models of progressively reduced glacier storage. However, societal forces establish the legal, economic, political, cultural, and social drivers that actually shape water usage patterns via human modification of watershed dynamics. This hydro-social framework has widespread implications for hydrological modeling in glaciated watersheds from the Andes and Alps to the Himalaya and Tien Shan, as well as for the development of climate change adaptation plans. [ABSTRACT FROM AUTHOR]

Summary: This paper presents an assessment of the impacts of climate change on a series of indicators of hydrological regimes across the global domain, using a global hydrological model run with climate scenarios constructed using pattern-scaling from 21 CMIP3 (Coupled Model Intercomparison Project Phase 3) climate models. Changes are compared with natural variability, with a significant change being defined as greater than the standard deviation of the hydrological indicator in the absence of climate change. Under an SRES (Special Report on Emissions Scenarios) A1b emissions scenario, substantial proportions of the land surface (excluding Greenland and Antarctica) would experience significant changes in hydrological behaviour by 2050; under one climate model scenario (Hadley Centre HadCM3), average annual runoff increases significantly over 47% of the land surface and decreases over 36%; only 17% therefore sees no significant change. There is considerable variability between regions, depending largely on projected changes in precipitation. Uncertainty in projected river flow regimes is dominated by variation in the spatial patterns of climate change between climate models (hydrological model uncertainty is not included). There is, however, a strong degree of consistency in the overall magnitude and direction of change. More than two-thirds of climate models project a significant increase in average annual runoff across almost a quarter of the land surface, and a significant decrease over 14%, with considerably higher degrees of consistency in some regions. Most climate models project increases in runoff in Canada and high-latitude eastern Europe and Siberia, and decreases in runoff in central Europe, around the Mediterranean, the Mashriq, central America and Brasil. There is some evidence that project change in runoff at the regional scale is not linear with change in global average temperature change. The effects of uncertainty in the rate of future emissions is relatively small. [Copyright &y& Elsevier]

Summary: The hydrological cycle has been substantially influenced by climate change and human activities. It is therefore of utmost importance to analyze the impact of climate change on hydrology, particularly on a regional scale, in order to understand potential future changes of water resources and water-related disaster, and provide support for regional water management. However, during the evaluation of climate change impact on hydrology or water resources, large uncertainty exists. In this paper, the Soil Water Assessment Tool (SWAT) model is used to investigate the potential impact of climate change on hydrology of the upper reaches of Qiantang River Basin, East China, for the future period 2011–2100. The uncertainty is considered by employing upgraded reliability ensemble averaged GCM climate projections under three emission scenarios A1B, A2 and B1 for three different stages of the future period. These projections are downscaled and used in the hydrological model. Impact of climate change on precipitation, potential evapotranspiraton and river runoff is then investigated. The model calibration and validation outcomes show reasonable performance of the SWAT model. The final results suggest that annual river runoff will likely decrease almost under all emission scenarios and time stages of the future period. Particularly, at Jinhua Station, substantial decrease of annual river runoff can be noticed, indicating less water resource possibly available for the region in future. Simulated monthly patterns show that the largest decrease will likely occur in winter while increases will occur in summer, implying possible more water-related disasters in this region. However, it is also noticed that the change signs/amount could be different under different emission scenarios and time stages, indicating large uncertainty involved in the impact analysis. [ABSTRACT FROM AUTHOR]

Summary: The focus of this paper is to understand the multi-decadal oscillatory component of variability in the Okavango River system, in southwestern Africa, and its potential evolution through the 21st century under climate change scenarios. Statistical analyses and hydrological modelling are used to show that the observed multi-decadal wet and dry phases in the Okavango River and Delta result from multi-decadal oscillations in rainfall, which are likely to be related to processes of internal variability in the climate system, rather than external natural or anthropogenic forcing. Analyses of changes in this aspect of variability under projected climate change scenarios are based on data from a multi-model ensemble of 19 General Circulation Models, which are used to drive hydrological models of the Okavango River and Delta. Projections for the 21st century indicate a progressive shift towards drier conditions attributed to the influence of increasing temperatures on water balance. It is, however, highly likely that multi-decadal oscillations, possibly of similar magnitude to that of 20th century, will be superimposed on the overall trend. These may periodically offset or amplify the mean drying trend. This effect should be accounted for in water and catchment management and climate change adaptation strategies. [Copyright &y& Elsevier]

Summary: Rapid land use/-cover change has increasingly transformed the hydrological functioning of tropical Andean ecosystems. The hydrological response to forest cover change strongly depends on the initial state of the ecosystem. Relatively little is known about human-disturbed ecosystems where forest plantations have been established on highly degraded land. In this paper, we analyze the impact of forest change on water and sediment fluxes for a highly degraded Andean catchment. Different pathways of land cover change (1963–2007) are observed in the Jadan catchment, with deforestation taking place in remote uplands and recovery and reforestation in the middle and lower parts where agricultural and bare lands are prevalent. Time series analyses of streamflow and rainfall data (1979/1982–2005/2007) show significant shifts in the distribution of rainfall and flow data. Changes in discharge are not resulting from changes in precipitation, as the direction of change is opposite. The removal of native forest for rangeland or croplands (by −20km2) is likely to have contributed to the increase in total annual water yield, through an increase in annual baseflow by 25mm. The observed changes in peakflow are important as the 1st percentile highest flow rates were 54% lower, while the 1st percentile rainfall amounts increased by 52%. The observed decrease in peakflow cannot be explained by clearcut of native forest, but is likely to be related to reforestation of degraded lands as well as spontaneous recovery of vegetation on remaining grazing lands. Over the same time period, a major decrease in specific sediment yields and suspended sediment loads was observed. Although deforestation in the upper parts led to increased landslide activity, this change is not reflected in an increased sediment yield. Small upland rivers are often nearly completely blocked by landslide material, thereby reducing their potential to transport sediment. In contrast, the reduction in estimated erosion is likely to be caused by the reduction of the degraded areas in areal extent as well as to the (partial) recovery of the vegetation in these areas. [Copyright &y& Elsevier]

Summary: The relationship between δ2H and δ18O in precipitation at a site, known as the local meteoric water line (LMWL), is normally defined using an ordinary least squares regression (OLSR) which gives equal weighting to all data points regardless of the precipitation amount they represent. However, smaller precipitation amounts are more likely to have a lower D-excess due to re-evaporation of raindrops below the cloud-base or biases in the sampling method. In this paper we present an equation for a precipitation amount weighted least squares regression (PWLSR) that will correct these biases for use in groundwater and surface hydrology applications. New LMWL equations are presented for Australian sites in the Global Network of Isotopes in Precipitation (GNIP), where the PWLSR consistently produces a LMWL with a larger gradient than the OLSR. Perth and Alice Springs exhibit the largest change in slope. This is consistent with the higher frequency of small monthly precipitation amounts with low D-excess values occurring at these sites in summer for Perth and throughout the year for Alice Springs. The PWLSR method was also applied to 288 stations in the GNIP data base (N >36) and the difference between the slopes of the LMWLs (Δa =slopePWLSR–slopeOLSR) calculated for these stations. The mean change in slope, Δa was 0.12 with 56% of sites showing an increase in slope or positive Δa value and 44% having a decrease in slope or negative Δa. Sites with Mediterranean climates showed the greatest increase in slope. The magnitude of the change in slope followed some general trends showing a positive correlation with average δ2H and δ18O composition and rainfall variability, and negative correlation with period of record (N). [ABSTRACT FROM AUTHOR]

Summary: Preserving natural wetlands is a growing challenge as the world faces increased demand for water. Drought, climate change and growing demands by users aggravate the issue. The conflict between irrigated agriculture and wetland services presents a classic case of competition. This paper examines an institutional mechanism that offers an incentive to farmers to adopt water conservation measures, which in turn could reduce overall water use in irrigated agriculture within a selected basin. Reduced water demands could provide the additional water needed for wetland preservation. We present an analytical empirical model implemented through the development of an integrated basin framework, in which least-cost measures for securing environmental flows to sustain wetlands are examined for the Zayandeh-Rud River Basin of central Iran. To test this idea, two policies – one with and one without an incentive – are analyzed: (a) reduced agricultural diversions without a water conservation subsidy, and (b) reduced agricultural diversions with a water conservation subsidy. The policies are evaluated against a background of two alternative water supply scenarios over a 10-year period. Results reveal that a water conservation subsidy can provide incentives for farmers to shift out of flood irrigation and bring more land into production by adopting water-saving irrigation technologies. The policy increases crop yields, raises profitability of farming, and increases the shadow price of water. Although the conservation subsidy policy incurs a financial cost to the taxpayer, it could be politically and economically attractive for both irrigators and environmental stakeholders. Results open the door for further examination of policy measures to preserve wetlands. [ABSTRACT FROM AUTHOR]

Summary: Despite the increasing use of regional climate model (RCM) simulations in hydrological climate-change impact studies, their application is challenging due to the risk of considerable biases. To deal with these biases, several bias correction methods have been developed recently, ranging from simple scaling to rather sophisticated approaches. This paper provides a review of available bias correction methods and demonstrates how they can be used to correct for deviations in an ensemble of 11 different RCM-simulated temperature and precipitation series. The performance of all methods was assessed in several ways: At first, differently corrected RCM data was compared to observed climate data. The second evaluation was based on the combined influence of corrected RCM-simulated temperature and precipitation on hydrological simulations of monthly mean streamflow as well as spring and autumn flood peaks for five catchments in Sweden under current (1961–1990) climate conditions. Finally, the impact on hydrological simulations based on projected future (2021–2050) climate conditions was compared for the different bias correction methods. Improvement of uncorrected RCM climate variables was achieved with all bias correction approaches. While all methods were able to correct the mean values, there were clear differences in their ability to correct other statistical properties such as standard deviation or percentiles. Simulated streamflow characteristics were sensitive to the quality of driving input data: Simulations driven with bias-corrected RCM variables fitted observed values better than simulations forced with uncorrected RCM climate variables and had more narrow variability bounds. [ABSTRACT FROM AUTHOR]

Summary: The climate scenarios of the IPCC suggest that adaptation to future climate change will be required. The North Sea Region, a marginal sea of the Atlantic Ocean between Great Britain, Scandinavia, Germany, the Netherlands and Belgium, is particularly affected due to rising sea level and a changing water balance. Water management plays a key role in sustainable management of natural and societal resources. This paper presents a participatory study of community approaches to regional adaptation to climate change. Water management adaptation options to regional climate induced changes until 2050 were developed together with stakeholders for the Wesermarsch County (Northern Germany). Available information on expected regional climate change and a modelling study on hydrological change suggested that adaptation of water management will be required until 2050. A regional stakeholder forum formulated a vision on how the Wesermarsch should look like in 2050. Following the holistic approach of collaborative planning, two stakeholder groups developed an adaptation portfolio on how urban and rural areas could adapt their water management to cope with the expected changes. Since most of the stakeholders do not want the county to undergo significant changes in terms of landscape and land use, they proposed technical measures to enforce flood protection and enhance the performance of the existing water management system. Adaptation in terms of land use change was not proposed although information on comparable examples from similar regions was available. To justify the proposed adaptation options, available information on expected climate change impacts was used selectively. Uncertainty in model projections was partly ignored to legitimate suggesting inflexible (technical) adaptation measures. However, collaborative planning proved to be helpful for a joint adaptation to climate change at the regional scale. Stakeholders as well as scientists took active part in the participatory learning process as required by EU directives. [Copyright &y& Elsevier]

Summary: This paper combines hydrological observations and modelling results of a semi arid catchment in Brazil that could lead to a better understanding of the hydrology of similar catchments in semi-arid regions. The Tapacurá catchment (area 470.5km2) in the Northeast of Brazil was selected for this study. The Distributed Catchment Scale Model, DiCaSM, was calibrated and validated for the stream flows of the Tapacurá catchment. The model performance was further tested by comparing simulated and observed scaled soil moisture. The results showed the ability of the model to simulate the stream flow and the scaled soil moisture. The simulated impacts of climate change of low emission (B1) scenarios, on the worst perspective, indicated the possibility of reduction in surface water availability by −13.90%, −22.63% and −32.91% in groundwater recharge and by −4.98%, −14.28% and −20.58% in surface flows for the time spans 2010–2039, 2040–2069, 2070–2099, respectively. This would cause severe impacts on water supply in the region. Changing the land use, for example by reforestation of part of the catchment area which is currently arable land, would lead to a decrease in both groundwater recharge by −4.2% and stream flow by −2.7%. Changing land use from vegetables to sugar cane would result in decreasing groundwater recharge by almost −11%, and increasing stream flow by almost 5%. The combination of possible impacts of climate change and land use requires a proper plan for water resources management and mitigation strategies. [Copyright &y& Elsevier]

Summary: This paper assesses the future variability of water resources in the short, medium and long terms over a large Sudano-Sahelian catchment in West Africa. Flow simulations were performed with a daily conceptual model. A period of nearly 50years (1952–2000) was chosen to capture long-term hydro-climatic variability. Calibration and validation were performed on the basis of a multi-objective function that aggregates a variety of goodness-of-fit indices. The climate models HadCM3 and MPI-M under SRES-A2 were used to provide future climate scenarios over the catchment. Outputs from these models were used to generate daily rainfall and temperature series for the 21st century according to: (i) the unbias and delta methods application and (ii) spatial and temporal downscaling. A temperature-based formula was used to calculate present and future potential evapotranspiration (PET). The daily rainfall and PET series were introduced into the calibrated and validated hydrological model to simulate future discharge. The model correctly reproduces the observed discharge at the basin outlet. The Nash-Sutcliffe efficiency criterion is over 89% for both calibration and validation periods, and the volume error between simulation and observation is close to null for the overall considered period. With regard to future climate, the results show clear trends of reduced rainfall over the catchment. This rainfall deficit, together with a continuing increase in potential evapotranspiration, suggests that runoff from the basin could be substantially reduced, especially in the long term (60–65%), compared to the 1961–1990 reference period. As a result, the long-term hydrological simulations show that the catchment discharge could decrease to the same levels as those observed during the severe drought of the 1980s. [Copyright &y& Elsevier]

Summary: This paper introduces an approach to route discharge with a variable river flow velocity based on the Manning–Strickler formula within large scale hydrological models. The approach has been developed for the global scale hydrological model WaterGAP and model results have been analyzed focusing on Europe. The goal was to find a method that is simple enough to derive the required parameters from globally available data while being sophisticated enough to deliver realistic flow velocity estimates for a large variety of environmental conditions. The river bed roughness (Manning’s n) is approximated in a spatially explicit way based on topography, the location of urban population, and river sinuosity. The hydraulic radius is estimated from actual river discharge, and river bed slope is derived by combining a high resolution DEM, a 5arc min drainage direction map, and river sinuosity. The modeled river flow velocity has been validated against data of US gauging stations. The representation of lateral transport has clearly been improved compared to the constant flow velocity applied in older model versions. The effect of incorporating variable flow velocities as compared to a constant flow velocity is largest on flood discharge, which generally increases in large rivers. The impact on monthly discharge hydrographs is marginal only. WaterGAP has been driven by three climate change projections for the 2050s to assess climate change impacts on flow velocity, and on the residence time of water in the European river system. Results indicate a decrease in residence times for Northern Europe and an increase for parts of the Mediterranean. [Copyright &y& Elsevier]

Summary: Water companies in the United Kingdom have considered climate change in their water resources plans for more than a decade through studies funded by UK Water Industry Research (UKWIR). This paper presents an initial assessment of the impact of the UK Climate Projections 2009 (UKCP09) on river flows at a national scale for the 2020s under the A1B scenario and the implications for water resource planning. A daily hydrological modelling framework based on two conceptual model structures and the Generalized Likelihood Uncertainty Estimation (GLUE) methodology has been applied to 70 catchments across the UK. A Latin Hypercube Sampling approach was adopted to handle the probabilistic nature of UKCP09. Results show a decrease in mean annual flow over most of the UK, with negative median values of all monthly changes except in winter over the western and northern mountainous areas. Furthermore the results indicate a high likelihood of a significant decline in summer flows. An analysis of variance shows that the main uncertainty in river flow changes comes from the spread in climate projections. Finally results are found to be consistent with a previous UKWIR assessment based on individual projections from 6 Global Climate Models (GCMs) under the A2 scenario. The reduction in summer low-flows, critical for water resources, appears however more limited with UKCP09. Although most expected changes are within natural variability, the drier conditions overall and the greater spread of results with respect to previous assessments indicates a need for testing the robustness of water resource plans. [Copyright &y& Elsevier]

Summary: Most of the plantation impact studies reported in literature normally use either one of the sensitivity-based approach or a hydrological model with few actually comparing the impact results from these different approaches. This paper investigates the impacts of increase or decrease in plantations and climate variability on streamflow using two approaches: the sensitivity-based approach (including a non-parametric model and six Budyko framework based models) and the hydrological modelling approach (using Xinanjiang and SIMHYD models) for three medium sized catchments in Australia. The results from the nine methods show that both plantation expansion/reduction and climatic differences can have major effects on catchment streamflow. There is a small variability in the reduction or increase in streamflow estimated by the nine methods. The results from this study show that the estimates of plantation impacts from the dynamic hydrological models are similar to those from the commonly used sensitivity-based approaches. The sensitivity-based approaches are only applicable where long term datasets are available and they only provide results at a mean annual time scale. The hydrological models simulate plantation impacted streamflow time series and so they can be used to estimate the relative contributions of land cover changes and climate change/variability at a daily, monthly or annual time-step. The outputs from the hydrological models can also be used to investigate the impacts of plantation expansion or reduction and climate change/variability on different runoff characteristics. [ABSTRACT FROM AUTHOR]

Summary: This paper describes a new method for the assessment of palaeohydrology through the Holocene. A palaeoclimate model was linked with a hydrological model, using a weather generator to correct bias in the rainfall estimates, to simulate the changes in the flood frequency and the groundwater response through the late Pleistocene and Holocene for the Wadi Faynan in southern Jordan, a site considered internationally important due to its rich archaeological heritage spanning the Pleistocene and Holocene. This is the first study to describe the hydrological functioning of the Wadi Faynan, a meso-scale (241km2) semi-arid catchment, setting this description within the framework of contemporary archaeological investigations. Historic meteorological records were collated and supplemented with new hydrological and water quality data. The modelled outcomes indicate that environmental changes, such as deforestation, had a major impact on the local water cycle and this amplified the effect of the prevailing climate on the flow regime. The results also show that increased rainfall alone does not necessarily imply better conditions for farming and highlight the importance of groundwater. The discussion focuses on the utility of the method and the importance of the local hydrology to the sustained settlement of the Wadi Faynan through pre-history and history. [ABSTRACT FROM AUTHOR]

Summary: Public water supply systems are designed to maintain water supply through extended periods of dry weather without excessive cost or environmental damage. During a drought, water suppliers can take further measures to enhance supplies or reduce demand. The introduction of drought measures is usually formalised in a drought plan, but there is often little evidence that the plan will prove successful during a range of feasible droughts. As the climate changes, recent hydrological data may be a poor guide to future drought, and planned actions may prove insufficient to maintain adequate water supplies. This paper describes a method for testing the resilience of water company drought plans to droughts that are outside recent hydrological experience. Long severe droughts of the nineteenth century provide an opportunity to test water supply system behaviour in a range of realistic droughts. The method developed combines system modelling with an interactive approach that asks water system managers to work through the actions that they would take at different stages of the drought, without knowledge of subsequent drought development. The approach was tested for two contrasting English water resource systems. In both cases, the existing water supply and drought planning measures succeeded in maintaining water supply, but significant demand restrictions and engineering measures had to be introduced. Wider use of the method by water supply planners should allow the refinement of drought and water supply plans, and will also create increased awareness of the actions necessary to manage a range of droughts. [ABSTRACT FROM AUTHOR]

Summary: This paper presents new rainfall and runoff data from a UK green roof test bed which has been collected almost-continuously over a 29-month period from 01/01/2007 to 31/05/2009. Overall, the monitoring period was fairly typical of the location’s long-term climatic averages, although the data set includes some extreme events in June 2007, which were associated with serious flooding locally. To focus on the system’s performance under rainfall events likely to be of interest from an urban drainage/stormwater management perspective, return period analysis has been applied to identify those storm events with a rainfall depth in excess of 5mm and a return period greater than one year. According to these criteria, 22 significant events have been identified, of which 21 have reliable runoff records. Overall the roof provided 50.2% cumulative annual rainfall retention, with a total volumetric retention equivalent to 30% during the significant events. The annual performance figures are towards the lower end of a range of international data, probably reflecting the fact that rainfall depths may be higher and evapotranspiration rates lower than in some more continental climatic settings. The roof’s finite retention depth means that the maximum possible retention percentage declines as storm depth increases, and retention varied from between 0 and 20mm, or 0% to 100%. Although some attenuation and delay of peak runoff is generally observed (mean peak flow reduction of 60% for the 21 significant events), the irregularity of natural rainfall patterns, combined with the variable influence of detention storage in specific events, makes the identification of peak-to-peak lag times difficult and arguably meaningless. Regression analyses have been undertaken to explore the potential to predict the roof’s hydrological performance as a function of storm characteristics. However, these are shown to have poor predictive capability, even for the system from which they were derived. Through a detailed examination of data from three contrasting events, it is argued that the inter-event processes are too complex to be captured by this type of modelling approach. Instead, an understanding of the hydrological processes affecting the flux of moisture into and out of the substrate is required to explain the observed runoff response. Locally-derived evapotranspiration rates and the roof’s observed maximum retention capacity are utilised to provide pragmatic guidance on the retention performance to be expected in response to selected design events. [ABSTRACT FROM AUTHOR]

Summary: Dryland salinity threatens many high-value assets in Australia. Assessing the technical feasibility of intervention requires consideration of spatial and temporal dimensions of land management and associated surface–groundwater interactions. This paper presents results regarding the practicability of protecting assets in a 371,000-ha agriculturally dominated catchment in south-eastern Australia using a physically-based catchment model, the Catchment Analysis Tool (CAT). The model links surface land management and hydrology at the paddock scale (daily time step growth and water use, crop rotations and management) with a fully distributed groundwater model enabling the assessment of agronomic versus engineering options for landscape asset protection. Scenarios assessing management options and costs of planting of perennial vegetation or engineering through groundwater pumping are outlined. The impacts of scenarios are reported under future climatic conditions as well as for the ‘steady state’ response. The study demonstrates a linked surface–groundwater modelling approach to estimate groundwater capture zones, response times to equilibrium under current and climate change conditions, as well as groundwater abstraction volumes required to protect landscape features. These factors are important considerations for evidence-based decision making about protecting assets from dryland salinity. [Copyright &y& Elsevier]

Summary: Bankfull flow is a relevant parameter in the field of large scale modelling especially for the analysis of environmental flows and flood related hydrological processes. In our case, bankfull flow data were required within the SCENES project in order to analyse ecological important inundation events at selected grid cells of a European raster. In practise, the determination of bankfull flow is a complex task even on local scale. Subsequent to a literature survey of bankfull flow studies, this paper describes a method which can be applied to estimate bankfull flow on a global or continental grid cell raster. The method is based on the partial duration series approach taking into account a 40-years time series of daily discharge data modelled by the global water model WaterGAP. An increasing threshold censoring procedure, a declustering scheme and the generalised Pareto distribution are applied. Modelled bankfull flow values are then validated by different efficiency criteria against bankfull flows observed at gauging stations in Europe. Thereby, the impact of (i) the applied distribution function, (ii) the threshold setting in the partial duration series, (iii) the climate input data and (iv) applying the annual maxima series are evaluated and compared to the proposed approach. The results show that bankfull flow can be reasonably estimated with a high model efficiency (E 1 =0.71) and weighted correlation (ωr 2 =0.90) as well as a systematic overestimation of 22.8%. Finally it turned out that in our study focusing on hydrological extremes, the appliance of the daily climate input data is a basic requirement. While the choice of the distribution function had no significant impact on the final results, the threshold setting in the partial duration series was crucial. [Copyright &y& Elsevier]

Summary: Global change encompasses changes in the characteristics of inter-related climate variables in space and time, and derived changes in terrestrial processes, including human activities that affect the environment. As such, projected global change includes groundwater systems. Here, groundwater is defined as all subsurface water including soil water, deeper vadose zone water, and unconfined and confined aquifer waters. Potential effects of climate change combined with land and water management on surface waters have been studied in some detail. Equivalent studies of groundwater systems have lagged behind these advances, but research and broader interest in projected climate effects on groundwater have been accelerating in recent years. In this paper, we provide an overview and synthesis of the key aspects of subsurface hydrology, including water quantity and quality, related to global change. Adaptation to global change must include prudent management of groundwater as a renewable, but slow-feedback resource in most cases. Groundwater storage is already over-tapped in many regions, yet available subsurface storage may be a key to meeting the combined demands of agriculture, industry, municipal and domestic water supply, and ecosystems during times of shortage. The future intensity and frequency of dry periods combined with warming trends need to be addressed in the context of groundwater resources, even though projections in space and time are fraught with uncertainty. Finally, potential impacts of groundwater on the global climate system are largely unknown. Research to improve our understanding of the joint behaviors of climate and groundwater is needed, and spin-off benefits on each discipline are likely. [Copyright &y& Elsevier]

Summary: This paper presents an analysis on the hydrological regimes from several rivers flowing from the western slope of the Andes Cordillera. We compiled a database of 40 unimpaired average monthly streamflow records located in central and southern Chile, spanning the region between latitudes 30°S and 40°S and the period between years 1961 and 2006. River categories encompass snowmelt, mixed and rainfall dominated watersheds. The water year hydrograph center of timing (CT) is used as an indicator of flow regime and as a proxy for streamflow distribution throughout the year. The CT for each river is correlated to local climatic variables such as seasonal temperature and precipitation, and to large-scale circulation indexes. We assess CT trends using the Mann–Kendall test for varying time windows within the study period. Overall results for the 1961–2006 period show a significant (95% confidence level) negative trend (CT date shifting towards earlier in the year) for 23 out of the 40 analyzed series. However, when studying time windows within the entire period there seems to be a break in the trend during the late 1970s, with positive or null changes for the latter half of the study period for most of the stations analyzed. We found that even though the CT is significantly correlated (r >0.5) to temperature indexes in the snowfed watersheds, there has been no significant change in CT timing for most of these watersheds despite documented warming on the region. CT for all types of watersheds present clear correlation to precipitation indexes (r >0.8), and we observed high and significant correlation between CT and ONI, SOI and MEI indexes for all the study region: higher (lower) precipitation amounts during El Niño (La Niña), rather than temperature variations, seem to be the most important factor controlling CT timing during these episodes. In order of importance, the CT showed higher correlation with annual precipitation amounts and timing, MEI, ONI and SOI, mean winter and spring temperature, and finally PDO. The detected trends are consistent only with trends in precipitation, as rivers that showed high correlation to temperature do not show any trend. These conclusions suggest that rivers on the region show a different response to temperature changes when compared to rivers of similar regime in the northern hemisphere, and that precipitation amount and timing are the source of most of the variability in streamflow timing for both snowmelt and rainfall dominated watersheds. Temperature induced variability in streamflow timing should be studied with more precise hydrological models, as the CT has a complex behavior due to multiple climatical dependencies. Studying such behavior using only historical data might be insufficient for drawing more precise conclusions. [Copyright &y& Elsevier]

Summary: Uncertainty estimation of climate change impacts has been given a lot of attention in the recent literature. It is generally assumed that the major sources of uncertainty are linked to General Circulation Models (GCMs) and Greenhouse Gases Emissions Scenarios (GGES). However, other sources of uncertainty such as the choice of a downscaling method have been given less attention. This paper focuses on this issue by comparing six downscaling methods to investigate the uncertainties in quantifying the impacts of climate change on the hydrology of a Canadian (Quebec province) river basin. The downscaling methods regroup dynamical and statistical approaches, including the change factor method and a weather generator-based approach. Future (2070–2099, 2085 horizon) hydrological regimes simulated with a hydrological model are compared to the reference period (1970–1999) using the average hydrograph, annual mean discharge, peak discharge and time to peak discharge as criteria. The results show that all downscaling methods suggest temperature increases over the basin for the 2085 horizon. The regression-based statistical methods predict a larger increase in autumn and winter temperatures. Predicted changes in precipitation are not as unequivocal as those of temperatures, they vary depending on the downscaling methods and seasons. There is a general increase in winter discharge (November–April) while decreases in summer discharge are predicted by most methods. Consistently with the large predicted increases in autumn and winter temperature, regression-based statistical methods show severe increases in winter flows and considerable reductions in peak discharge. Across all variables, a large uncertainty envelope was found to be associated with the choice of a downscaling method. This envelope was compared to the envelope originating from the choice of 28 climate change projections from a combination of seven GCMs and three GGES. Both uncertainty envelopes were similar, although the latter was slightly larger. The regression-based statistical downscaling methods contributed significantly to the uncertainty envelope. Overall, results indicate that climate change impact studies based on only one downscaling method should be interpreted with caution. [Copyright &y& Elsevier]

Summary: This paper provides a general overview of changes in flooding caused by climate change in Finland for the periods 2010–2039 and 2070–2099. Changes in flooding were evaluated at 67 sites in Finland with variable sizes of runoff areas using a conceptual hydrological model and 20 climate scenarios from both global and regional climate models with the delta change approach. Floods with a 100-year return period were estimated with frequency analysis using the Gumbel distribution. At four study sites depicting different watershed types and hydrology, the inundation areas of the 100-year floods were simulated with a 2D hydraulic model. The results demonstrate that the impacts of climate change are not uniform within Finland due to regional differences in climatic conditions and watershed properties. In snowmelt-flood dominated areas, annual floods decreased or remained unchanged due to decreasing snow accumulation. On the other hand, increased precipitation resulted in growing floods in major central lakes and their outflow rivers. The changes in flood inundation did not linearly follow the changes in 100-year discharges, due to varying characteristics of river channels and floodplains. The results highlight the importance of comprehensive climatological and hydrological knowledge and the use of several climate scenarios in estimation of climate change impacts on flooding. Generalisations based on only a few case studies, or large scale flood assessments using only a few climate scenarios should be avoided in countries with variable hydrological conditions. [ABSTRACT FROM AUTHOR]

Summary: Climate change will change availability, quality and allocation of regional water resources. Appropriate modelling tools should therefore be available to realistically describe reactions of watersheds to climate change and to identify efficient and effective adaptation strategies on the regional scale. The paper presents the hydrologic model PROMET (Processes of Radiation, Mass and Energy Transfer), which was developed within the GLOWA-Danube project as part of the decision support system DANUBIA. PROMET covers the coupled water and energy fluxes of large-scale (A ∼100,000km2) watersheds. It is fully spatially distributed, raster-based with raster-elements of 1km2 area, runs on an hourly time step, strictly conserves mass and energy and is not calibrated using measured discharges. Details on the model concept and the individual model components are given. An application case of PROMET is given for the mountainous Upper-Danube watershed in Central Europe (A =77,000km2). The water resources are intensively utilized for hydropower, agriculture, industry and tourism. The water flows are significantly influenced by man-made structures like reservoirs and water diversions. A 33-years model run covering the period from 1971 to 2003 using the existing meteorological station network as input is used to validate the performance of PROMET against measured stream flow data. Three aspects of the model performance were validated with good to very good results: the annual variation of the water balance of the whole watershed and selected sub-watersheds, the daily runoff for the whole period at selected gauges and the annual flood peaks and low flows (minimum 7-days average). PROMET is used to investigate the impact of climate change on the water cycle of the Upper Danube. A stochastic climate generator is fed with two scenarios of climate development until 2060. One assumes no future temperature change, the other uses the temperature trends of the IPCC-A1B climate change scenario. PROMET is run with both climate data sets. No change in low-flow is detected when no temperature change is assumed. The IPCC-A1B climate scenario results in marked decreases of low-flow at the outlet of the watershed. [Copyright &y& Elsevier]

Summary: The Gourma site in Mali is one of the three instrumented meso-scale sites deployed in West-Africa as part of the African Monsoon Multi-disciplinary Analysis (AMMA) project. Located both in the Sahelian zone sensu stricto, and in the Saharo–Sahelian transition zone, the Gourma meso-scale window is the northernmost site of the AMMA-CATCH observatory reached by the West African Monsoon. The experimental strategy includes deployment of a variety of instruments, from local to meso-scale, dedicated to monitoring and documentation of the major variables characterizing the climate forcing, and the spatio-temporal variability of surface processes and state variables such as vegetation mass, leaf area index (LAI), soil moisture and surface fluxes. This paper describes the Gourma site, its associated instrumental network and the research activities that have been carried out since 1984. In the AMMA project, emphasis is put on the relations between climate, vegetation and surface fluxes. However, the Gourma site is also important for development and validation of satellite products, mainly due to the existence of large and relatively homogeneous surfaces. The social dimension of the water resource uses and governance is also briefly analyzed, relying on field enquiry and interviews. The climate of the Gourma region is semi-arid, daytime air temperatures are always high and annual rainfall amounts exhibit strong inter-annual and seasonal variations. Measurements sites organized along a north–south transect reveal sharp gradients in surface albedo, net radiation, vegetation production, and distribution of plant functional types. However, at any point along the gradient, surface energy budget, soil moisture and vegetation growth contrast between two main types of soil surfaces and hydrologic systems. On the one hand, sandy soils with high water infiltration rates and limited run-off support almost continuous herbaceous vegetation with scattered woody plants. On the other hand, water infiltration is poor on shallow soils, and vegetation is sparse and discontinuous, with more concentrated run-off that ends in pools or low lands within structured endorheic watersheds. Land surface in the Gourma is characterized by rapid response to climate variability, strong intra-seasonal, seasonal and inter-annual variations in vegetation growth, soil moisture and energy balance. Despite the multi-decadal drought, which still persists, ponds and lakes have increased, the grass cover has largely recovered, and there are signs of increased tree cover at least in the low lands. [Copyright &y& Elsevier]

Summary: The distribution-free Mann–Kendall test is widely used for the assessment of significance of trends in many hydrologic and climatic time series. Previous studies have suggested both exact and approximate formulas for the calculation of the variance of the test statistic when the data are serially correlated. This paper outlines a procedure for the calculation of the exact distribution of the Mann–Kendall trend test statistic for persistent data with an arbitrary correlation structure. The particular cases of the AR(1) (first order autoregressive) model and the Fractional Gaussian Noise (FGN) model are presented for sample sizes between 3 and 9. While it has been previously shown that the Normal distribution gives a reasonable approximation to the exact distribution for large values of sample size n, a more accurate approximation based on the Beta distribution is proposed for moderate values of n. The application of the test to small samples is illustrated by testing the significance of recent trends starting in 1990 in 58 world river flow time series. The results confirm the effect of scaling in small samples and the benefits of using the Beta distribution as an approximation. [Copyright &y& Elsevier]

Summary: Evaporation is an important part of the water balance of a catchment, and estimates of potential evaporation (PE) are an important input to hydrological models. When modelling the hydrological impacts of climate change, using data from climate models, present models generally do not provide direct estimates of PE from the land surface. Estimates thus have to be calculated from other climate variables, and many existing formulae can be applied. This paper compares the well-established, more physically based but data-intensive, Penman–Monteith PE against a simple, temperature-based (T-based) PE, when calculated from readily available monthly climate model data over Britain (for five global and eight regional climate models). The performance of the two PE formulations is compared to MORECS PE (a gridded dataset derived by the UK Met Office from weather observations, using a modified Penman–Monteith formulation) for the baseline period 1961–1990, and the changes in the two PE estimates between the 1970s and the 2080s are compared. The results show that the T-based PE matches MORECS PE better than does Penman–Monteith PE, for all the climate models studied. However, the changes in the two types of PE between the 1970s and 2080s are different, for each of the climate models, and these affect the modelled hydrological impacts. This is illustrated using three example catchments spread across Britain. The uncertainty introduced by the PE formulation is less than that due to the climate model, but could still be important for some applications. [Copyright &y& Elsevier]

Abstract: The perception of a changing climate, which impacts also hydrological processes, is now generally admitted. However, the way of handling the changing nature of climate in hydrologic practice and especially in hydrological statistics has not become clear so far. The most common modelling approach is to assume that long-term trends, which have been found to be omnipresent in long hydrological time series, are ‘deterministic’ components of the time series and the processes represented by the time series are nonstationary. In this paper, it is maintained that this approach is contradictory in its rationale and even in the terminology it uses. As a result, it may imply misleading perception of phenomena and estimate of uncertainty. Besides, it is maintained that a stochastic approach hypothesizing stationarity and simultaneously admitting a scaling behaviour reproduces climatic trends (considering them as large-scale fluctuations) in a manner that is logically consistent, easy to apply and free of paradoxical results about uncertainty. [Copyright &y& Elsevier]

Abstract: One of the more important questions in hydrology is: if the climate warms in the future, will there be an intensification of the water cycle and, if so, the nature of that intensification? There is considerable interest in this question because an intensification of the water cycle may lead to changes in water-resource availability, an increase in the frequency and intensity of tropical storms, floods, and droughts, and an amplification of warming through the water vapor feedback. Empirical evidence for ongoing intensification of the water cycle would provide additional support for the theoretical framework that links intensification with warming. This paper briefly reviews the current state of science regarding historical trends in hydrologic variables, including precipitation, runoff, tropospheric water vapor, soil moisture, glacier mass balance, evaporation, evapotranspiration, and growing season length. Data are often incomplete in spatial and temporal domains and regional analyses are variable and sometimes contradictory; however, the weight of evidence indicates an ongoing intensification of the water cycle. In contrast to these trends, the empirical evidence to date does not consistently support an increase in the frequency or intensity of tropical storms and floods. [Copyright &y& Elsevier]

• Hydrological responses to land use and climate change are simulated using integrated modelling. • Scoring method is applied to select representative climate models. • Mean temperature is likely to increase by 1.79 °C (3.57 °C) under mid (high) emission scenarios. • Annual and monsoon flow is likely to increase during the 2050s and 2080s. • Hydrological sensitivity of the basin is analysed against changes in climatic variables. Accurate spatial and temporal measurement of water budget play a crucial role in achieving the sustainable planning and management of water resources. This paper presents a comprehensive integrated approach to simulate hydrological responses under dynamics of land use land cover (LULC) and climate change scenarios over Upper Narmada Basin, India. In order to select the representative climate models, scoring method was applied at regional scale. Best five performing climate models (MIROC5, CNRM-CM5, MPI-ESM-LR, GFDL-ESM2G and IPSL-CM5A-MR) were coupled with semi-distributed hydrological model to simulate the hydrological responses. Considering the heterogeneity of the large basin, multi-site calibration and parameters sensitivity analysis were performed using Sequential Uncertainty Fitting (SUFI-2) algorithm. To compute the hydrological sensitivity against land use change, calibrated model was coupled with historical and futuristic land use scenarios (1990, 2000, 2010 and 2030). The results indicate intensified precipitation towards the late 21st century, whereas annual mean temperature could be raised by 1.79 °C and 3.57 °C under mid and high emission scenarios respectively, at the end of century. Annual and monsoon flow in the basin likely to increase during the 2050 s (2041–2070) and 2080 s (2071–2100). Moreover, the relation between climate variables and water budget components were identified to analyse the hydrological sensitivity of the basin under changing climate. [ABSTRACT FROM AUTHOR]

Conceptual schema illustrating the buffering role of groundwater during future summer low-flow periods in an alpine catchment. It shows the evolution of monthly mean recharge, snow water equivalent and discharge in the reference and the future period 2085 for a scenario RCP 8.5 with a strong increase in temperatures and decrease in summer precipitations. • Quaternary deposits play a critical role in seasonally storing alpine groundwater. • In future summer, the decrease in alpine discharge depends on groundwater storage. • The actual winter low flow appears as a lower bound for the future summer low flow. Alpine environments are particularly vulnerable to climatic warming, and long term observations suggest a shift of snow-influenced river discharge towards earlier periods of the year. For water resources management, the seasonal patterns of discharge in alpine areas are particularly relevant, as the shift to lower flows in summer and autumn combined with increased water demand could lead to water shortage in downstream catchments. The storage of groundwater in alpine catchments could significantly modulate how changing climatic conditions influence the annual streamflow regime. However, groundwater storage and its buffering capacity in alpine areas remain poorly understood. Moreover, studies on how climate change will impact water resources in alpine areas rarely consider the influence of geology. In this paper, catchment geology is used as a basis for the classification of future summer low flows behavior of several alpine catchments in Switzerland. Based on the analysis of the relationship between low-flow indicators and geology, the role of unconsolidated quaternary deposits is explored. We show that quaternary deposits play a critical role in the seasonal storage of groundwater, which can contribute to rivers during low-flow periods. Three climate change simulations based on extreme RCP 8.5 scenarios are fed into a conceptual hydrological model to illustrate the buffering role of groundwater. Past and future low flows normalized by mean past and future streamflows appear correlated with the percentage of unconsolidated quaternary deposits. These results highlight that catchments with high groundwater contribution to streamflow relative to precipitation will have a slower decrease in future summer discharge. Therefore, we propose two indicators that can be used to anticipate the response of future summers low flows in alpine areas to climate change: the current winter low flows and the percentage of unconsolidated quaternary deposits of the catchments. [ABSTRACT FROM AUTHOR]