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• A MGWR-based SMAP soil moisture product downscaling method is proposed. • The method considers the scale differences in the impact of surface variables on soil moisture. • Field validation shows higher accuracy from the downscaled SM than the SMAP SM itself. • This proposed downscaling method performs better than the traditional GWR and MW methods in the semiarid area. Passive microwave remote sensing missions such as Soil Moisture Active Passive (SMAP) are widely used for global soil moisture (SM) estimation. But the low spatial resolution of passive microwave SM products limits their applications at regional and local scales (normally 1–10 km). Using high-resolution auxiliary data to downscale passive microwave SM products is the primary way to obtain high-resolution SM data. However, the existing SM downscaling methods do not entirely account for the scale differences in the impact of various variables on the distribution of SM. To solve this problem, this paper introduced MGWR (Multiscale Geographically Weighted Regression) as a novel way to analyze the scale differences of normalized difference vegetation index (NDVI) and land surface temperature (LST) on the spatial pattern of SM. Accordingly, a new spatial downscaling algorithm for SMAP SM products is proposed and compared with the geographically weighted regression (GWR) algorithm and moving window algorithm (MW). The algorithm was applied to data taken during the SMAP Validation Experiment 2016 (SMAPVEX16), and the downscaled SM evaluated with in situ SM and aircraft observations. These results show that: 1) the SM downscaling conversion function, based on the MGWR, effectively reveals how different surface parameters relate to SM, with LST influencing SM globally and NDVI affecting it locally, 2) compared with GWR and MW, the 1 km SM obtained by the MGWR-based downscaling method showed better spatial agreement with airborne SM in the semiarid region with the ubRMSE decreasing by 0.023 m3/m3 and 0.026 m3/m3 for GWR and MW respectively, 3) when evaluating the 1 km SM with in situ SM in the semiarid region, the SM obtained through MGWR exhibited lower ubRMSE values as compared to both GWR and MW. Specifically, the median ubRMSE values for MGWR, GWR, and MW were 0.043 m3/m3, 0.053 m3/m3, and 0.094 m3/m3, respectively. In conclusion, this study demonstrates that MGWR can effectively improve the accuracy of downscaled SM in semiarid regions. [ABSTRACT FROM AUTHOR]

Highlights • Interception accounted for 24.0% of total rainfall. • Throughfall accounted for 69.8% of total rainfall, increasing towards subhumid sites. • Stemflow accounted for 6.2% of total rainfall, decreasing towards subhumid sites. • Shrubs presented higher stemflow and lower throughfall percentages than trees. • Higher stemflow percentage of dry sites was explained by higher abundance of shrubs. Abstract The net amount of rainfall entering into the soil and its spatial distribution at the patch scale are key drivers of ecosystem processes in drylands. The spatial distribution of water is mainly controlled by vegetation canopy which determines the partitioning of rainfall into interception, throughfall and stemflow. In this paper, we synthesized and analyzed rainfall partitioning for 68 woody plant species in drylands (delimited by a rainfall-potential evapotranspiration ratio <0.65; 46 papers). We explored the role of rainfall inputs and plant morphological attributes (life form, phenology, leaf type and bark type) by considering a rainfall gradient from 145 to 805 mm year−1. On average, interception, throughfall and stemflow accounted for 24.0, 69.8 and 6.2% of total rainfall, respectively. Stemflow was the most variable flux (coefficient of variation = 107.8%), while interception and throughfall were less variable fluxes (coefficient of variation = 39.2 and 20.4%, respectively). Along the increasing rainfall gradient, interception showed a tendency to decrease from 27.1 to 18.9% (p = 0.12), throughfall increased from 61.4 to 81.2% (p < 0.01) and stemflow decreased from 10.0 to 1.6% (p < 0.0001). Shrubs presented higher stemflow than trees (9.4% vs. 3.5%, respectively; p < 0.0001), while trees presented higher throughfall than shrubs (72.3% vs. 63.0%, respectively; p < 0.05). Species with smooth barks presented higher stemflow than species with rough barks (8.3% vs. 4.2%, respectively; p < 0.0001). Both phenology and leaf type had no effect on interception, throughfall and stemflow (p > 0.05 for all cases). Shrubs were more abundant towards the dry edge of the rainfall gradient (145–500 mm year−1), while trees were more abundant towards the subhumid edge (500–805 mm year−1). These results suggested that higher stemflow found towards the dry edge of the rainfall gradient was caused by the higher abundance of shrubs, which generated more stemflow than trees. Our findings highlighted the ecohydrological key role of vegetation life form and rainfall inputs affecting the amount of water entering into the soil and its spatial distribution in drylands. [ABSTRACT FROM AUTHOR]

Highlights • Proposing soil mulching for enhancing groundwater resources and a model to assess it. • Assessing the use of various mulches in increasing deep percolation of rainfalls. • Deep percolation rate is higher in precipitations with shorter time intervals. Abstract In this paper, a model is proposed for the assessment of the effectiveness of various mulches in increasing deep percolation of rainfalls for enhancing arid zones aquifers. For this purpose, 8 precipitations were selected from the Intensity-Duration-Frequency (IDF) curves of the study area with a return period of 2 and 5 years. The deep percolation of these precipitations were examined in lysimeters with gravel, sand and mixed mulches and without any mulch. Then 192 data of soil moisture, daily maximum air-temperature and deep percolation were measured for driving empirical equations. Moreover, the efficiency and accuracy of these empirical equations were investigated using Coefficient of Determination (CD) and Nash–Sutcliffe Efficiency Coefficient (NSEC). The results showed that the obtained empirical equations could estimate deep percolation and evaporation with an acceptable accuracy. Using these equations and the soil-water balance equation, a soil moisture model was developed for the assessment of deep percolation. Then it was examined to evaluate the efficiency of the mulched soils in increasing soil moisture and aquifer recharging of three years' precipitations in Shahrekord plain, Iran. The results showed that the deep percolation increased in all examined mulched soils compared to unmulched soil, its maximum and cumulative increase were in gravel mulch with 21.3% and 30%, respectively. Furthermore, groundwater modeling results showed that the mulching could improve groundwater level as 0.34 m over a three year period. Finally, this paper proposes soil mulching for enhancing groundwater resources and a model to assess it. [ABSTRACT FROM AUTHOR]

[Display omitted] • Five discharge datasets have median correlation coefficients > 0.6 with the observations. • Overestimation of monthly mean flow is more common than underestimation. • GRFR showed the best estimate at around 40% of the locations. • None of the models provides good estimates for rivers and streams in arid regions. High-resolution global flow discharge datasets are critical to understand the terrestrial water cycle and river ecosystem services. Recently, a number of global hydrological models have been developed to capture global river flow dynamics at locally relevant scales. However, the relative accuracy of these simulated flow discharges is largely unknown. In this paper, using the largest observed streamflow datasets from > 26,000 gauging stations, we evaluated the performance of monthly and sub-monthly flow variation (1980–2014) generated from five major global hydrological models, Catchment-based Macro-scale Floodplain model (CaMa-Flood), Global Flood Awareness System (GloFAS-reanalysis), Global Reach-level Flood Reanalysis (GRFR), PCRaster GLOBal Water Balance model (PCR-GLOBWB), and Water Global Assessment and Prognosis (WaterGAP). Significant spatial heterogeneity in model performance was identified. We found that estimates by all five discharge datasets have a relatively high correlation with the observations (medians > 0.6). But none of them showed adequate correlations between simulated and observed flows for systems in Southwest or Central U.S.A., South Africa, or South Australia. Across all models, overestimation of monthly mean flow was more common than underestimation and high flows at a sub-monthly scale were more accurately characterized than low flows. Performance of all models was poor in Africa and Oceania. No single model performed universally best at all gauging stations, but GRFR showed the best estimate at around 40 % of the locations. None of the models provided satisfying estimates for rivers and streams in arid regions. We also found a significant negative effect of flow regulation on the predictive accuracy of all models. Our study highlights the importance of thorough evaluation of global discharge datasets before their local and regional application and provides guidance for future enhancement of global hydrological models. [ABSTRACT FROM AUTHOR]

• Drought followed by extreme rain/flooding exposed vulnerabilities in Ceará, Brazil. • Adaptative strategies in dry periods may become maladaptive during extreme rain. • Impacts of and responses to drought, extreme rain, and flooding are interrelated. • Hydrometereological extremes should be considered together in semi-arid regions. As climates continue to change, semi-arid rainfall regimes are projected to become increasingly more extreme, with longer dry periods and fewer, but more intense, heavy rainfall events. This process of hydroclimatic intensification increases the risk associated with successive extreme climate hazards, such as drought and then heavy rainfall, in the same area. However, the development of effective adaptation strategies to drought, heavy rainfall, and flood hazards is hampered by the lack of integrated analyses that consider the interactions among these hazards and responses to them. To increase understanding of these interactions, this paper examines impacts of and adaptive actions taken in response to prolonged drought (2012–2018) and subsequent extreme rainfall and flooding (March and April 2023) in the semi-arid region of Ceará, Northeast Brazil. We find that policies and adaptive measures focus primarily on drought hazard, while preparation for extreme rainfall events and flooding is scant. Management plans and long-term adaptive strategies are being developed for drought and not other extreme hydrometeorological events. Additionally, emergency measures for extreme rainfall and flooding are much less structured than those for drought. As such, the paradigm "Convivência com o semiárido" ("Living with the semi-arid region") remains limited to adapting to drought hazard, ultimately hindering adequate extreme rainfall and drought responses. To promote more effective adaptive strategies in the context of hydroclimatic intensification in semi-arid regions, drought, heavy rainfall, and flood responses must be considered in a more integrated manner to create management plans to prepare for the potential impacts of these hazards into the future. [ABSTRACT FROM AUTHOR]

Summary Growing water extractions combined with emerging demands for environment protection increase competition for scarce water resources worldwide, especially in arid and semiarid regions. In those regions, climate change is projected to exacerbate water scarcity and increase the recurrence and intensity of droughts. These circumstances call for methodologies that can support the design of sustainable water management. This paper presents a hydro-economic model that links a reduced form hydrological component, with economic and environmental components. The model is applied to an arid and semiarid basin in Southeastern Spain to analyze the effects of droughts and to assess alternative adaptation policies. Results indicate that drought events have large impacts on social welfare, with the main adjustments sustained by irrigation and the environment. The water market policy seems to be a suitable option to overcome the negative economic effects of droughts, although the environmental effects may weaken its advantages for society. The environmental water market policy, where water is acquired for the environment, is an appealing policy to reap the private benefits of markets while protecting ecosystems. The current water management approach in Spain, based on stakeholders’ cooperation, achieves almost the same economic outcomes and better environmental outcomes compared to a pure water market. These findings call for a reconsideration of the current management in arid and semiarid basins around the world. The paper illustrates the potential of hydro-economic modeling for integrating the multiple dimensions of water resources, becoming a valuable tool in the advancement of sustainable water management policies. [ABSTRACT FROM AUTHOR]

• Understanding the riparian zone from the watershed river-groundwater transformation. • Revealing the contributions of groundwater to landscape ecological patterns. • Proposing pathways to maintain a healthy landscape ecological pattern. In arid and semiarid areas with scarce precipitation, strong evaporation, and fragile ecosystems, rivers and groundwater interact frequently. Dynamic hydrological changes and solute transport jointly determine the evolution of the landscape in riparian zones, resulting in the formation of a landscape ecological pattern in arid areas that is unique and includes a system of rivers and lakes. In recent decades, unsustainable and mono-purpose grey infrastructure has been implemented in many arid areas, and the effect of river-groundwater interactions on the landscape ecological pattern in riparian zones has often been neglected. These processes have triggered variations in or even the reversal of landscape ecological patterns in these arid areas. This study selected the arid and semiarid basin in northwestern China as the study area. Multiple methods were used to study the evolution of the landscape ecological pattern in the riparian zones driven by typical hydrological processes from the perspective of river-groundwater transformation. Three results were obtained from the analysis: (1) The driving force of the evolution was identified, and the spatial geological heterogeneity, meteorological and hydrological conditions, and river-groundwater interactions played dominant roles in the evolution of the landscape ecological pattern in the riparian zones. (2) Human activities and climate change controlled the direction and intensity of landscape evolution. (3) Pathways for maintaining a healthy landscape ecological pattern in riparian zones and suggestions for identifying the key issues that should be studied in the future were proposed. This paper primarily contributes to a better understanding of landscape ecological patterns in the riparian zone in arid areas from the watershed river-groundwater transformation perspective, thereby promoting integrated watershed management. [ABSTRACT FROM AUTHOR]

Summary: In this paper, the trends of the annual streamflow and precipitation and cross correlations between them were analyzed in nine large river basins of China during 1956–2005. The results indicate that: (1) the annual mean streamflow decreases in arid and semi-arid regions of north China; however, increasing trends occur in south and Southwest China; (2) the annual streamflow and precipitation exhibit reasonable correlation in nine large river basins except those located in inland areas. The annual streamflow over most areas of China is fed by precipitation; however, the decline in streamflow is faster than the decreases of precipitation since 1970s in the arid and semi-arid regions of north China. The relationship between the annual precipitation and streamflow presents a non-stationary state in north China. This non-stationary relationship is strongly influenced by both human activities and precipitation changes; (3) a significant increase of water use might be the major factor responsible for the steeper decline in streamflow than in precipitation in Haihe River, Yellow River and Songliao River basins in north China. In inland river areas, increase of water use and actual evapotranspiration might result in decline in streamflow although precipitation has an increase tendency. This paper sheds light on the non-stationary relationship between annual precipitation and streamflow and possible underlying causes, which will be helpful for a better understanding of the changes of precipitation and streamflow in China at large scale and in other regions of the world. [Copyright &y& Elsevier]

Summary: Among the three sites distributed along the West African latitudinal gradient in the AMMA-CATCH observation system, the experimental setup in the Niamey area of south-west Niger samples the cultivated Sahel environment, for hydrological, vegetation and land surface processes. The objective is to investigate relationships between climate, land cover, and the water cycle, in a rapidly changing semiarid environment. This paper first presents the main characteristics of the area, where previous research, including the EPSAT and HAPEX-Sahel experiments, had evidenced a widespread decadal increase in water resources, concurrently with severe drought conditions. The specifics of AMMA-CATCH research and data acquisition at this site, over the long-term (∼2001–2010) and enhanced (∼2005–2008) observation periods, are introduced. Objectives and observation strategy are explained, and the main characteristics of instrument deployment are detailed. A very large number of parameters – covering rainfall, vegetation ecophysiology, phenology and production, surface fluxes of energy, water vapour and CO2, runoff and sediment, pond water, soil moisture, and groundwater – were monitored at local to meso scales in a nested structure of sites. The current state of knowledge is summarized, connecting processes and patterns of variation for rainfall, vegetation/land cover, and the terrestrial hydrologic cycle. The central role of land use and of its spectacular change in recent decades is highlighted. This paper provides substantial background information that sets the context for papers relating to the south-west Niger site in this AMMA-CATCH special issue. [Copyright &y& Elsevier]

Abstract: The paper of proposes a statistical approach for a multi-layered system in order to determine intrinsic characteristics of each aquifer and the mixing ratios in places where leakage exists and applies it in central Niger. Despite of its potential interest, the paper misses its objective because (i) it relies on a poor knowledge of the regional literature, (ii) it suffers from internal inconsistency and (iii) it lacks validation. Many previous publications dedicated to semiarid areas (e.g. ) showed that considering various temporal and spatial scales and crossing different methods is often the only key to reliable results. The authors unintentionally demonstrate the limits of a too rapid monothematic study in a region where exchanges between aquifers are often complex. Concrete drawbacks of such a self-limitation are illustrated in this comment. [Copyright &y& Elsevier]

The drought in the African Sahel, persisting since 1968, emphasizes the vulnerability of local water resources to climatic variations and land use changes in this semiarid environment. Following the Hapex–Sahel experiment (1992–1994), research aims at understanding and modeling the impact on the hydrological cycle of these changing climatic and environmental conditions over a 1500-km2 area east of Niamey, Niger. The hydrological landscape consists of a myriad of small endoreic catchments feeding temporary or permanent pools from which water percolates to an unconfined aquifer. As the first step in a local-to-regional scale approach to the water resource recharge in the area, a physically based rainfall–runoff model is developed for a typical, 1.9-km2 endoreic system named Wankama, which is monitored continuously since 1992. This first of two companion papers describes the key elements of the hydrological landscape, the experimental setup with which the Wankama catchment and pool are monitored, the r.water.fea distributed hydrological model and its application to the construction of the Wankama catchment model. Because of the difficulties of long-term field experimentation in the region, not all observed events can be considered equally well recorded; in particular, detection of exogenous water inflow occurrences that may alter Wankama runoff estimates is needed. The paper describes the careful, model-aided data analysis performed in order to select the observation set with which the model can most reliably be tuned and operated. In this rainfall–runoff data analysis phase, the model is used prior to any calibration. Model calibration and verification, including output uncertainty, are the subject of the second paper [J. Hydrol. (2003)]. All steps of analysis and modeling were performed on the 1992–1998 data only, before the 1999–2000 data became available, and are tested a posteriori against the latter. [Copyright &y& Elsevier]

In this paper, a comprehensive and interdisciplinary framework for management of eutrophication in off-stream artificial lakes in semi-arid and arid regions is proposed. Identification of the lake’s water resources system components and stakeholders, simulation of Phosphorus (P) export from upstream watershed, simulation of the lake water quality as well as simulation of water demands and supply, development of management scenarios for the lake and selecting the best scenario using social choice methods (i.e. discrete and fuzzy Borda counts) are the four main parts of the framework. The proposed framework is applied on Chitgar Artificial Lake (ChAL), the largest intra-urban artificial lake in Tehran which has been constructed in 2010–2013 for recreational purposes. The Load Apportionment Model (LAM) is used for the simulation of P loads from the point and non-point (diffusive) sources and the LakeMab model is used for the simulation of P dynamics in the lake. The management scenarios contain optimized rule curves for water intake/outtake blended with P management plans (i.e. removal of point sources of P load in the upstream watershed, construction of a hydroponic bio-filter or an advanced water treatment plant beside the lake for reduction of external loading of P and recycling lake water, alum treatment of lake sediments for controlling the internal loading of P as well as construction of a dry detention basin). The most preferred scenarios selected by the discrete Borda count are the low-cost alum treatment and dry detention basin, while the most preferred scenario according to fuzzy Borda count, which considers the uncertainty of model inputs, is the costly water treatment plant. In all preferred scenarios, water intake is conducted from flood flows in order to avoid conflict with downstream agricultural demands. In addition to decentralized decision making and stakeholders’ participation, the proposed framework promotes the integration of the technical aspects such as the role of internal loading in lake eutrophication and separation of flood and non-flood flows in the off-stream lakes’ systems. [ABSTRACT FROM AUTHOR]

• Optical images are easily affected by clouds and cloud shadows. • Fmask is introduced into the GEE platform and modified for Sentinel-2 images. • The improved SNOWL algorithm considers unstable snow cover areas. • Snow cover extraction accuracy in flat surface and shady slope is the highest. • Snow cover in mountainous is reconstructed by combing the Fmask, Sen2Cor and the improved SNOWL algorithms. Snow is an important type of surface cover and an important freshwater resource in the arid regions of northwest China, and optical satellites are an important means for monitoring variation in snow cover. However, the radiation values measured by satellite sensors are affected by cloud cover and cloud shadows; thus, the reconstruction of snow cover under clouds and cloud shadows becomes a bottleneck problem especially in mountains areas. Based on the digital elevation model (DEM), in this paper, an integrated method of snow cover reconstruction on Sentinel-2 images is created by combining the improved SNOWL (snow line) algorithm considering unstable snow cover areas, Fmask cloud detection algorithms, and the Sen2Cor clear sky snow cover detection tool with a geospatial processing platform, GEE (Google Earth Engine). Considering the Babao River Basin as the study area, 474 Sentinel-2 scenes (10 m) were selected to obtain the snow cover spatiotemporal variations of 158 days from November 2016 to March 2021. Compared with the high-resolution GF-2 satellite images, the integrated method can extract snow under clouds and cloud shadows well, and the improved SNOWL algorithm improves the overall accuracy from 66.05 % to 84.26 %. The experimental results show that approximately half of the Babao River Basin is unstable snow cover, and areas above 3977 m are covered with snow for at least half a year. [ABSTRACT FROM AUTHOR]

Data limitations on groundwater (GW) recharge over large areas are still a challenge for efficient water resource management, especially in semi-arid regions. Thus, this study seeks to integrate hydrological cycle variables from satellite imagery to estimate the spatial distribution of GW recharge in the Ipanema river basin (IRB), which is located in the State of Pernambuco in Northeast Brazil. Remote sensing data, including monthly maps (2011–2012) of rainfall, runoff and evapotranspiration, are used as input for the water balance method within Geographic Information Systems (GIS). Rainfall data are derived from the TRMM Multi-satellite Precipitation Analysis (TMPA) Version 7 (3B43V7) product and present the same monthly average temporal distributions from 15 rain gauges that are distributed over the study area (r = 0.93 and MAE = 12.7 mm), with annual average estimates of 894.3 (2011) and 300.7 mm (2012). The runoff from the Natural Resources Conservation Service (NRCS) method, which is based on regional soil information and Thematic Mapper (TM) sensor image, represents 29% of the TMPA rainfall that was observed across two years of study. Actual evapotranspiration data, which were provided by the SEBAL application of MODIS images, present annual averages of 1213 (2011) and 1067 (2012) mm. The water balance results reveal a large inter-annual difference in the IRB GW recharge, which is characterized by different rainfall regimes, with averages of 30.4 (2011) and 4.7 (2012) mm year −1 . These recharges were mainly observed between January and July in regions with alluvial sediments and highly permeable soils. The GW recharge approach with remote sensing is compared to the WTF (Water Table Fluctuation) method, which is used in an area of alluvium in the IRB. The estimates from these two methods exhibit reliable annual agreement, with average values of 154.6 (WTF) and 124.6 (water balance) mm in 2011. These values correspond to 14.89 and 13.53% of the rainfall that was recorded at the rain gauges and the TMPA, respectively. Only the WTF method indicates a very low recharge of 15.9 mm for the second year. The values in this paper provide reliable insight regarding the use of remotely sensed data to evaluate the rates of alluvial GW recharge in regions where the potential runoff cannot be disregarded from WB equation and must be calculated spatially. [ABSTRACT FROM AUTHOR]

This paper considers the imbalanced binary classification problem by focusing on the application of the short-term rainfall forecasting in arid and semi-arid regions. Specifically, we present a novel boosting-type method by utilizing the generalized extreme value (GEV) distribution as the link function and applying a gradient tree boosting algorithm to capture complex interactions among covariates. The proposed method has several appealing advantages such as, it can identify rare rainfall events as well as quantifying the uncertainties; it is data-driven that without any assumption on the relationship between the covariates and the rainfall event; the fitted model is highly interpretable, making it a useful tool for studying the rainfall mechanisms in arid and semi-arid regions. Experiments on two real-world datasets show that our approach outperforms its competing methods. • Propose the generalized extreme value distribution as the skewed link function. • Employ the gradient tree boosting to capture complex interactions among covariates. • Can identify the rare rainfall events as well as quantifying the uncertainties. • No assumption on the relationship between the covariates and the rainfall event. • The model for fitting the imbalanced data is highly interpretable. [ABSTRACT FROM AUTHOR]

In recent years, ecological degradation caused by irrational groundwater exploitation has been of growing concern in arid and semiarid regions. To address the groundwater-ecological issues, this paper proposes a groundwater-resource exploitation mode to evaluate the tradeoff between groundwater development and ecological environment in the northern Tianshan Mountains, northwest China’s Xinjiang Uygur Autonomous Region. Field surveys and remote sensing studies were conducted to analyze the relation between the distribution of hydrological conditions and the occurrence of ecological types. The results show that there is a good correlation between groundwater depth and the supergene ecological type. Numerical simulations and ecological assessment models were applied to develop an ecology-oriented exploitation mode of groundwater resources. The mode allows the groundwater levels in different zones to be regulated by optimizing groundwater exploitation modes. The prediction results show that the supergene ecological quality will be better in 2020 and even more groundwater can be exploited in this mode. This study provides guidance for regional groundwater management, especially in regions with an obvious water scarcity. [ABSTRACT FROM AUTHOR]

This paper presents a study of the potential for green infrastructure (GI) to restore the predevelopment hydrologic cycle in a semi-arid urban catchment. Simulations of stormwater runoff from a 0.11-km 2 urban catchment in Salt Lake City, Utah, USA for predeveloped (Natural Hydrology, NH), developed (Baseline, BL), and developed with GI (Green Infrastructure, GI) conditions were executed for a one-year period. The study was repeated for a relatively dry year, wet year, and an average year based on precipitation amounts in the year. Bioretention and green roofs were chosen for the GI plan. Results showed that the water budget of the catchment with the GI plan implemented more closely matches the NH water budget compared to the BL scenario, for all three years (dry, wet, average). The BL and GI scenarios showed more significant modifications to the water budget than what has been found by studies in humid climates. Compared to the BL condition, GI annually reduces surface runoff by 35%, 45%, and 43% and restores evapotranspiration by 18%, 19%, and 25% for the dry, average, wet years, respectively. Based on the introduced water budget restoration coefficient (WBRC), the water budget of the study catchment was restored by the GI plan to 90%, 90%, and 82% of the predevelopment state in the dry, average, and wet years, respectively. By comparing the WBRC estimated for other studies, it is further inferred that the water budget is more significantly affected by development and GI restoration in semi-arid than humid climates, but the differences lessen as the precipitation amount increases. [ABSTRACT FROM AUTHOR]

The water resources in the arid region of northwestern China, which are impacted by climate change, tend to be more unstable, and the environment and ecosystems will suffer from severe water shortage. In this paper, potential future climate trends were predicted based on CMIP5 simulations in this region. The water availability and agricultural water demand under future climate change scenarios were estimated. Impacted by increases in temperature, the irrigation water demand will increase by 4.27–6.15 billion m 3 in this region over the next 60 years, compared to the demand of 32.75 billion m 3 during 1971–2000. However, the annual runoff will only increase by 4.8–8.5 billion m 3 , which is equivalent to or even less than the increased irrigation water demand. In fact, the increased demand for industrial, domestic and ecological water were not considered here. Thus, the water supply/demand contradiction will result in more severe water shortages in the future. According to a comparison with simulated irrigation water demand under three adaptation strategy scenarios, we should take effective measures such as improving the efficiency of irrigation water utilization, reducing crop planting areas and adjusting crop planting structures to alleviate the impacts of future climate changes and human activities on the water supply and water use in this region. [ABSTRACT FROM AUTHOR]

Summary Drylands cover approximately one-third of the Earth’s surface, are home to nearly 40% of the Earth’s population and are characterised by limited water resources and ephemeral river systems with an extremely variable flow regime and high transmission losses. These losses include actual evaporation, infiltration to the soil and groundwater and residual (terminal) water remaining after flood events. These critical components of the water balance of dryland river systems remain largely unknown due to the scarcity of observational data and the difficulty in accurately accounting for the flow distribution in such large multi-channel floodplain systems. While hydrodynamic models can test hypotheses concerning the water balance of infrequent flood events, the scarcity of flow measurement data inhibits model calibration, constrains model accuracy and therefore utility. This paper provides a novel approach to this problem by combining modelling, remotely-sensed data, and limited field measurements, to investigate the partitioning of flood transmissions losses based on seven flood events between February 2006 and April 2012 along a 180 km reach of the Diamantina River in the Lake Eyre Basin, Australia. Transmission losses were found to be high, on average 46% of total inflow within 180 km reach segment or 7 GL/km (range: 4–10 GL/km). However, in 180 km reach, transmission losses vary non-linearly with flood discharge, with smaller flows resulting in higher losses (up to 68%), which diminish in higher flows (down to 24%) and in general there is a minor increase in losses with distance downstream. Partitioning these total losses into the major components shows that actual evaporation was the most significant component (21.6% of total inflow), followed by infiltration (13.2%) and terminal water storage (11.2%). Lateral inflow can be up to 200% of upstream inflow (mean = 86%) and is therefore a critical parameter in the water balance and transmission loss calculations. This study shows that it is possible to constrain the water balance using hydrodynamic models in dryland river systems using remote sensing and simple field measurements to address the otherwise scarce availability of data. The results of this study also enable a better understanding of the water resources available for ecosystems in these unique multi-channel and large floodplain rivers. The combined modelling/remote sensing approach of this study can be applied elsewhere in the world to better understand the water balances and water transmission losses, important drivers of ecohydrological processes in dryland environments. [ABSTRACT FROM AUTHOR]

• A stakeholder-based framework is proposed for groundwater resources management. • Some resilience-based criteria are used for evaluating management scenarios. • Power and interest of each stakeholder is evaluated using the rough set theory. • Evidential reasoning approach incorporates quantitative and qualitative criteria. • The methodology can be easily applied to other groundwater systems. In this paper, a new stakeholder-based framework is proposed for groundwater resources management in arid regions. In this framework, rough set theory is used for the probabilistic classification of stakeholders considering their powers and interests, which are obtained from stakeholder analysis. Then, a system dynamics model is developed to evaluate the physical, economic, environmental, and social conditions of the system corresponding to each defined water resources management scenario. Moreover, an evidential reasoning approach is used to estimate the resilience of scenarios based on seven generic resilience principles. Finally, based on the results of stakeholder analysis, system dynamics modeling, and resilience analysis, groundwater management scenarios are ranked using a proposed social choice procedure called Electoral College Voting. The results of applying the methodology to the Rafsanjan plain in Iran illustrate that a scenario that includes modern irrigation systems and water transfer is the socially optimal scenario in the study area. Implementing this scenario reduces water consumption by 40%, improves the resilience of groundwater by about 50% and helps the aquifer to be recovered. [ABSTRACT FROM AUTHOR]

Summary Watershed models play an important role in modern water resource management, increasingly demanding a robust hydrologic data framework to estimate watershed hydrochemical processes. The Generalized Watershed Loading Function (GWLF), a typical watershed model with modest data requirements, has been applied to watershed-scale hydrochemical estimation worldwide. However, while it generally successfully estimates flows in humid regions, the model suffers from a weakness in hydrologic estimation during low-flow periods, which are projected to continue increasing with global climate change in many places. To address this issue, three algorithms describing functional responses of flows to saturated water storage, the segment function approach, linear function approach, and exponential function approach, have been proposed in this paper, integrated with a previous leakage mechanism for unsaturated water storage used in two earlier GWLF versions, and applied to a case study of Shuai Shui River watershed in China. Comparisons of this version, including new algorithms or algorithm linkages, with the earlier GWLF versions, show that all the new algorithms improve model accuracy in low-flow months; the linear function approach linking the leakage process has the best effect. This work refines the framework of GWLF model to address both humid and arid conditions that can be used as alternatives for future applications. These new functional dynamic responses should also have potential application in other similar watershed models. [ABSTRACT FROM AUTHOR]

Summary To face the problem of groundwater depletion, the Indian Government relies on large projects of Managed Aquifer Recharge (MAR). Numerous recharge structures such as percolation tanks exist but the impact of these structures on groundwater resources remains poorly understood. Although the evaporation/infiltration ratio of percolation tanks was determined in several studies in semi-arid contexts using surface water balance methods, few studies evaluated the impact on the aquifer recharge. However, knowledge on recharge dynamics over time and space is essential for (1) the quantitative evaluation of stored water volumes, (2) the identification of beneficiaries (farmers) and (3) the estimation of percolation tanks recharge zone to the extent that is required to define proper management regulations at basin scale. These three points are of prime importance in the case of semi-arid regions where a limited number of rain events determine the water stored over the entire year. Assessment of the stored groundwater is even more difficult in crystalline aquifers due to the heterogeneous structure of flow paths. To date no methodological guidelines exist for local assessment of percolation tanks in crystalline aquifers. In this paper, we develop a method for calculating a local groundwater budget and we compare it with a computed surface balance. The method is applied to a case study in semi-arid crystalline context. From the groundwater balance we draw conclusions on (1) the limited amount of stored water in the aquifer, (2) the delayed recharge of the aquifer highlighting temporary storage/slow groundwater movement in the unsaturated zone and (3) the limited number of beneficiaries in years of medium monsoon rainfall. These results complement the understanding of the hydrodynamic functioning of percolation tanks, and their impact on the local groundwater balance. [ABSTRACT FROM AUTHOR]

Summary In water resources modeling, meteorological data scarcity can be compensated by various global data sets, but those data sets can differ tremendously. In the literature, hydrological models of differing complexity are proposed for estimating the water resources of semi-arid catchments, and also to evaluate rainfall data sets. The goal of this paper is to provide a joint analysis of modeling uncertainty due to different input data and increasing model complexity. Impacts of mutually concealed uncertainties on model performance and model outputs are exemplified in two data sparse semi-arid catchments in Ethiopia. We applied a semi-distributed and a fully distributed hydrological model, having different levels of complexity. Three different satellite-based rainfall data sets and two temperature products were used as model inputs. The semi-distributed model demonstrated good validation performances, while the fully distributed model was more sensitive to data uncertainties. The application of TRMM version 6 completely failed and the high-resolution CMORPH precipitation estimate outperformed TRMM version 7. In contrast, the use of high-resolution temperature data did not improve the model results. The large differences in remotely sensed input data were buffered inside the hydrological models. Therefore, data set evaluations regarding only the simulated hydrographs were less meaningful. In contrast, the investigation of parameter evolution and distributed outputs’ variability appeared to be a valuable tool to uncover the interdependencies of data and model uncertainties. We suggest this procedure to be applied by default in water resources estimations that are affected by data scarcity, but especially when data sets are evaluated using hydrological models. Our case study demonstrates that estimations of groundwater recharge and actual evapotranspiration vary largely, depending on the applied data sets and models. The joint analysis reveals large interdependencies between data and model evaluations. It shows that traditional studies focusing only on one part of uncertainty, either the input uncertainty or the uncertainty arising from the choice of model structure are limited in their explanatory power of the modeling performance, particularly in poorly gauged regions. [ABSTRACT FROM AUTHOR]

Summary Understanding the fresh groundwater lens (FGL) behavior and potential threat of climatic-induced seawater intrusion (SWI) are significant for the future water resources management of many small islands. In this paper, the FGL of Kish Island, an arid-region case in the Persian Gulf, Iran, is modeled using two-dimensional (2D) and three-dimensional (3D) simulations. These simulations are based on the application of SUTRA, a density-dependent groundwater numerical model. Also, the numerical model parameters are calibrated using PEST, an automated parameter estimation code. Firstly a detailed conceptualization of the FGL model is completed to understand the sensitivity of the FGL to some particular aspects of the model prior to analysis of climate change simulations. For these investigations, the FGL system is defined based on Kish Island system to accomplish the integrated comparison of features of a conceptual model that are representative of real-world systems. This is the first study which adopts such an approach. The comparison of cross-sectional simulations suggests that the two-layer properties of the Kish Island aquifer have a significant influence on the FGL while the impacts of lateral-boundary irregularities are negligible. The impacts of sea-level rise (SLR), associated land-surface inundation (LSI), and variations in recharge rate on the FGL salinization of Kish Island are investigated numerically. Variations of SLR value (1–4 m) and net recharge rate (17–24 mm/year) are considered to cover a possible range of climatic scenarios in this arid-region island. The 2D and 3D simulation results demonstrate that LSI caused by SLR and recharge rate variation impacts are more important factors in the FGL in comparison to estimated SLR impacts without LSI. It is also shown that climate change impacts on the FGL are long-term to reach a new FGL equilibrium in the case of Kish Island’s aquifer system. The comparative analysis of 2D and 3D results shows that three-dimensionality is a significant factor, especially in large-scale 3D systems of small islands. The results of this study are expected to have implications for the understanding and management of the fresh groundwater resources of Kish Island and are also expected to be relevant to the study of the impact of climate change on groundwater resources on islands worldwide. [ABSTRACT FROM AUTHOR]

• Developing the stream-groundwater system evolutional states theoretical framework; • Refining four different system states; • Proposing critical conditions for different evolutional states; • Revealing the evolutional process of stream leakage flux; • Evaluating the impact of parameters on the critical moment of the system. Losing streams are widespread in arid and semi-arid regions. Exploring the evolutional states of losing stream-groundwater systems is of great significance to understand the exchanges of water, mass and energy in stream-aquifer systems. This study is devoted to investigate the evolutional process of infiltration flux, pressure head and flow states of a seasonally losing stream-groundwater system with the semi-permeable streambeds missing (or without clogging). The paper constructs a new theoretical framework for the evolutional states of the system. In particular, it focuses on investigating the transition among different evolutional states including disconnected state, transitional state, negative-pressure connected state and positive-pressure connected state, and the critical conditions of transition between connected and disconnected states. The critical conditions associated with disconnection or connection are that 1) the zero-flux zone starts to disappear, 2) the unsaturated zone starts to disappear, and 3) the negative pressure zone starts to disappear. Analytical solutions of those critical conditions are proposed. The evolutional process of stream leakage is characterized into two stages: the first stage corresponds to the disconnected and transitional states in which the seepage fluxes decrease with time; the second stage corresponds to the fully connected state in which the seepage flux decreases rapidly again as time developing. Finally, the influence of various controlling parameters on the critical conditions is analyzed. The critical time (t CRI 1) and critical depth (z CRI 1) of changing from the disconnected state to the transitional state have nonlinear correlations with saturated hydraulic conductivity (K s), pore-size distribution index (λ) and flux at the base of the unconfined aquifer (q). The critical time (t CRI 2) and the critical depth (z CRI 2) of changing from the transitional state to the negative-pressure connected state and the critical time (t CRI 3) of changing from the negative-pressure connected state to the positive-pressure connected state all have nonlinear correlations with K s and λ. z CRI 1 and z CRI 2 are independent of saturated water content (θ s) and residual water content (θ r). An innovative physical interpretation is given to system evolutional states and quantifiable criteria for those evolutional states are proposed. The findings of this study can help better understand the evolutional states of seasonally losing stream-groundwater systems, and it lays a foundation for further research on water exchange, mass transport and ecological protection in stream-groundwater systems. [ABSTRACT FROM AUTHOR]

Summary: The arid agricultural lands of the Monegros Desert, in the central Ebro Basin (NE Spain), show contrasting white patches (WPs) and dark patches (DPs), evidencing their different soil composition. The white patches have shallow soils with low or nil crop development in most years. Soil at the dark patches uses to be deeper, and winter cereal attains better development. This paper analyzes soil hydro-physical features in order to identify differences in soil physical properties between white and dark soils. For this purpose, 20 pairs of WP/DP soils were studied on several agricultural plots. Each sampled pair was under the same soil condition. Three soil treatment (ST) were studied: freshly tilled soil (MB), cropped (C), and fallowed soil (F). The gypsum and calcium carbonate content, organic matter (OM) content, and particle size distribution for the 0–10cm depth soil were determined. Field measurements for the 1–10cm depth soil layer were soil bulk density (ρb ), soil penetration resistance (SPR), saturated hydraulic conductivity (K 1–10) and sorptivity (S 1–10). The water retention curve (WRC) was determined in the lab on undisturbed soil cores for the 1–10cm depth soil layer. Additional field measurements of soil surface crust sorptivity (Scrust ) and hydraulic conductivity (Kcrust ) at saturation were also performed. The results show that WP soils have significantly (p <0.05) higher contents of gypsum, lower contents of calcium carbonate and OM, and a coarser texture than DP soils. Compared to DP, the WP soils have higher values of SPR but lower ρb , K and S values in both the surface crust and the 0–10cm depth soil layer. On average, K 1–10 in DP was 1.4times higher than that measured in WP. DP showed a better-defined microstructure and retained more water retention at near saturation conditions than WP. Soil treatments have a significant effect on ρb , SPR, S 1–10, K 1–10 and on the WRC parameters. Overall, ρb and SPR was the lowest under MB, with maximal S 1–10 and K 1–10 values under C. Compared to C and F, MB presented the highest volume of structural porosity and the lowest water retention at near saturation conditions. [Copyright &y& Elsevier]

Summary: Soil moisture is an effective water source for plant growth in the semi-arid Loess Plateau of China. Characterizing the response of deep soil moisture to land use and afforestation is important for the sustainability of vegetation restoration in this region. In this paper, the dynamics of soil moisture were quantified to evaluate the effect of land use on soil moisture at a depth of 2m. Specifically, the gravimetric soil moisture content was measured in the soil layer between 0 and 8m for five land use types in the Longtan catchment of the western Loess Plateau. The land use types included traditional farmland, native grassland, and lands converted from traditional farmland (pasture grassland, shrubland and forestland). Results indicate that the deep soil moisture content decreased more than 35% after land use conversion, and a soil moisture deficit appeared in all types of land with introduced vegetation. The introduced vegetation decreased the soil moisture content to levels lower than the reference value representing no human impact in the entire 0–8m soil profile. No significant differences appeared between different land use types and introduced vegetation covers, especially in deeper soil layers, regardless of which plant species were introduced. High planting density was found to be the main reason for the severe deficit of soil moisture. Landscape management activities such as tillage activities, micro-topography reconstruction, and fallowed farmland affected soil moisture in both shallow and deep soil layers. Tillage and micro-topography reconstruction can be used as effective countermeasures to reduce the soil moisture deficit due to their ability to increase soil moisture content. For sustainable vegetation restoration in a vulnerable semi-arid region, the plant density should be optimized with local soil moisture conditions and appropriate landscape management practices. [Copyright &y& Elsevier]

Summary: A large part of the world faces the problem of aridity, e.g. in Australia, the semi-arid and arid regions occupy about 50–75% of the country. There is a serious lack of data on many key hydrological processes in the arid regions, which makes it difficult to understand the hydrological processes in these regions. Although arid regions are characterised by a very low mean annual rainfall, it can experience severe flooding causing widespread damage. In hydrological literature, there is a limited presence of the application of regional flood frequency analysis (RFFA) studies for the world arid regions due to limited data availability. This paper presents a RFFA study for the semi-arid and arid regions of Australia using the most up-to-date data set and compares the results with that of the world data. It has been found that arid catchments exhibit a higher loss and lower runoff coefficient values as expected. Based on four model selection criteria and L-moments ratio diagram, it has been found that a Generalised Pareto distribution is preferable to the Exponential distribution to fit the partial duration series flood data in the arid regions of Australia. It has also been found that the arid region exhibits much steeper flood frequency growth curve than that of the humid region and the growth curve gets steeper with the decreasing mean annual rainfall. The developed growth curve for the semi-arid and arid region of Australia is found to be similar to other typical semi-arid and arid regions of the world. The developed prediction equation for the mean annual flood in the semi-arid and arid region of Australia uses two readily obtainable predictor variables (catchment area and design rainfall intensity), which can be used along with the developed growth curve to estimate design floods for the ungauged catchments in these regions with reasonable accuracy. The growth curve developed in this study is primarily applicable to the semi-arid and arid regions of Australia; however, this may be adapted to other similar regions of the world along with the locally developed prediction equation for the scaling factor (i.e. mean annual flood in this case) to derive preliminary design flood estimates. [Copyright &y& Elsevier]

Summary: The optimal use of available resources is of paramount importance in the backdrop of the increasing food, fiber, and other demands of the burgeoning global population and the shrinking resources. The optimal use of these resources can be determined by employing an optimization technique. The comprehensive reviews on the use of various programming techniques for the solution of different optimization problems have been provided in this paper. The past reviews are grouped into nine sections based on the solutions of the theme-based real world problems. The sections include: use of optimization modelling for conjunctive use planning, groundwater management, seawater intrusion management, irrigation management, achieving optimal cropping pattern, management of reservoir systems operation, management of resources in arid and semi-arid regions, solid waste management, and miscellaneous uses which comprise, managing problems of hydropower generation and sugar industry. Conclusions are drawn where gaps exist and more research needs to be focused. [Copyright &y& Elsevier]

Summary: This paper presents an energy balance modelling approach to predict the nightly water yield and the surface temperature (T f) of two passive radiative dew condensers (RDCs) tilted 30° from horizontal. One was fitted with a white hydrophilic polyethylene foil recommended for dew harvest and the other with a black polyethylene foil widely used in horticulture. The model was validated in south-eastern Spain by comparing the simulation outputs with field measurements of T f and dew yield. The results indicate that the model is robust and accurate in reproducing the behaviour of the two RDCs, especially in what refers to T f, whose estimates were very close to the observations. The results were somewhat less precise for dew yield, with a larger scatter around the 1:1 relationship. A sensitivity analysis showed that the simulated dew yield was highly sensitive to changes in relative humidity and downward longwave radiation. The proposed approach provides a useful tool to water managers for quantifying the amount of dew that could be harvested as a valuable water resource in arid, semiarid and water stressed regions. [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 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: Urban irrigation is an important component of the hydrologic cycle in many areas of the arid and semiarid western United States. This paper describes a new approach that uses readily available datasets to estimate the location and rate of urban irrigation. The approach provides a repeatable methodology at 1/3km2 resolution across a large urbanized area (500km2). For this study, Landsat Thematic Mapper satellite imagery, air photos, climatic records, and a land-use map were used to: (1) identify the fraction of irrigated landscaping in urban areas, and (2) estimate the monthly rate of irrigation being applied to those areas. The area chosen for this study was the San Fernando Valley in Southern California. Identifying irrigated areas involved the use of 29 satellite images, air photos, and a land-use map. The fraction of a pixel that consists of irrigated landscaping (Firr ) was estimated using a linear-mixture model of two land-cover endmembers (selected pixels within a satellite image that represent a targeted land-cover). The two endmembers were impervious and fully-irrigated landscaping. In the San Fernando Valley, we used airport buildings, runways, and pavement to represent the impervious endmember; golf courses and parks were used to represent the fully irrigated endmember. The average Firr using all 29 satellite scenes was 44%. Firr calculated from hand-digitizing using air photos for 13 randomly selected single-family-residential neighborhoods showed similar results (42%). Estimating the rate of irrigation required identification of a third endmember: areas that consisted of urban vegetation but were not irrigated. This “nonirrigated” endmember was used to compute a Normalized Difference Vegetation Index (NDVI) surplus, defined as the difference between the NDVI signals of the irrigated and nonirrigated endmembers. The NDVI signals from irrigated areas remains relatively constant throughout the year, whereas the signal from nonirrigated areas rises and falls seasonally due to precipitation. The areas between airport runways were chosen to represent the nonirrigated endmember. Water-delivery records from 65 spatially-distributed single-family neighborhoods, consisting of nearly 1800 homes, were correlated with the NDVI surplus. The results show a strong exponential correlation (r 2 =0.94). In the absence of water-delivery records, which can be difficult to obtain, a surrogate was identified: the landscape evapotranspiration rate (ET L ). ET L was used to scale NDVI surplus (which is dimensionless) to irrigation rates using an exponential scaling function. The monthly irrigation rates calculated from satellite and climatic data compared well with irrigation rates calculated from actual water-delivery data using a paired Wilcoxan signed-rank test (p =0.0063). Identification of Firr at the pixel scale, along with identification of the irrigation rate for a fully-irrigated pixel, allows for mapping of urban irrigation over large areas. Maps showing the location and rate of monthly irrigation for the San Fernando study area were computed for January and August 1997. [ABSTRACT FROM AUTHOR]

Summary: This paper analyses the dew collection performance of two polyethylene (PE) foils in a semi-arid region (Southern Spain). The dew collecting devices consisted of two commercial passive radiative dew condensers (RDCs) of 1m2 tilted to 30°. They were fitted with two different high-emissivity PE foils: a white hydrophilic foil (WSF) recommended as standard for dew recovery comparisons by the International Organization for Dew Utilization (OPUR), and a low-cost black PE foil (BF) widely used for mulching in horticulture. Dew yield, foil surface temperature and meteorological variables (air temperature, relative humidity, downward long wave radiation and wind speed) were recorded hourly during a 1-year period from May-2009 to May-2010. The spectral emissivity of the foils was determined in laboratory in the range 2.5–25μm and the radiance-weighed values were calculated over different intervals, indicating that BF emitted more than WSF, especially in the range 2.5–7μm. Dew yield was well correlated with the air relative humidity and foil net radiation in both foils and was hardly detected when the relative humidity was lower than 75% or the wind speed higher than 1.5ms−1. WSF was more sensitive to dew formation due to its hydrophilic properties, registering more dewy nights (175) than BF (163) while the annual cumulative dew yield for BF was higher (20.76mm) than for WSF (17.36mm) due to the higher emissivity and emitted radiance of BF. These results suggested that increasing the surface emissivity over the whole IR spectrum could be more effective for improving RDC yield performances than increasing the surface hydrophilic properties. On a practical point of view, BF could be considered as a suitable material for large scale RDCs, as in our study it presented several advantages over the reference material, such as higher dew collection performance, longer lifespan and much lower cost. [Copyright &y& Elsevier]

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]

Abstract: Severe and more persistent droughts in the arid regions such as the western US have increased the interest in cloud seeding programs or weather modification (WM) operations to increase precipitation. An anticipated increase in precipitation could augment annual and seasonal streamflow and reduce the impacts during dry periods. This paper evaluates hydrological impacts of WM operations in the North Platte River watershed, by utilizing a hydrologic model. The Variable Infiltration Capacity (VIC) land surface hydrological model is calibrated and validated for the periods of 1950–80 and 1981–2000 respectively, using daily meteorological forcing and monthly streamflow data. Two sets of WM scenarios are developed and forced into the VIC model to quantify the impacts of increased precipitation on streamflow. The first scenario is based on existing WM operations in the State of Wyoming. The second scenario hypothetically apply WM throughout the watershed to identify suitable regions for cloud seeding operations. For the first scenario, an increase of 0.3–1.5% in annual streamflow is observed from model simulations for a 1–5% increase in precipitation. Follow-on scenarios have identified the central-west and south-west regions of the watershed, which consist of a higher coverage of Evergreen Needleleaf Forest, to generate higher streamflow during WM operations. The north-east and north-west regions, which consist of a higher coverage of open shrublands and grasslands, are found to generate lower increases in streamflow during these operations. The observed annual precipitation is higher for central and southern regions when compared to northern regions of the watershed. It can be considered that the simulated changes in streamflow from different regions could also be attributed to variation in annual precipitation distribution within the watershed rather than solely based on cloud seeding operations. For the proposed WM programs or programs that are claimed effective based on precipitation augmentation, the hydrological impacts can be evaluated based on this analysis. [Copyright &y& Elsevier]

Summary: This paper deals with the assessment of sustainability in the exploitation of groundwater by agriculture in arid and semi-arid lands. The procedure proposed is not based on an indicator made up of a few partial, static figures, but on one which requires the use of all the information collectable for the system under assessment. This information serves to calibrate a dynamic model which formalizes the main causal chains and feedbacks existing between hydrogeology and the number of farms, this being ultimately linked to farms economy. The risk of overexploitation is worked out as the percentage of model’s long-term steady-states, associated to a great number of different scenarios, surpassing some chosen threshold marking out sustainability from degradation. The procedure has been implemented for two study cases: the Eastern La Mancha aquifer (Spain), where information was abundant, and the Oued-Mird alluvial aquifer (Morocco), where quantitative information was so much scarcer. Significant risks of degradation have been found in both cases, especially in the Moroccan one. [Copyright &y& Elsevier]

Summary: The study examines the possibility of simulating time series of streamflows for poorly gauged catchments based on hydrological similarity. The data of 11 gauged catchments (475–2522km2), located in the mountainous semi-arid Karkheh river basin of Iran, is used to develop the procedure. The well-known HBV model is applied to simulate daily streamflow with parameters transferred from gauged catchment counterparts. Hydrological similarity is defined based on four similarity measures: drainage area, spatial proximity, catchment characteristics and flow duration curve (FDC). The study shows that transferring HBV model parameters based on the FDC similarity criterion produces better runoff simulation compared to the other three methods. Furthermore, it is demonstrated that the FDC based regionalization of HBV model parameters works reasonably well for streamflow simulations in the data limited catchments in the mountainous parts of the Karkheh river basin. In addition, it could be demonstrated that the parameter uncertainty of the model has little impact on the FDC based regionalization approach. The methodology presented in this paper is easy to replicate in other river basins of the world, particularly those facing decline in streamflow monitoring networks and with a limited number of gauged catchments. [ABSTRACT FROM AUTHOR]

Summary: Recharge is a key component of the hydrological balance in groundwater systems. Particularly in arid and semiarid settings recharge often takes place during isolated rainfall episodes. As a result pumping might cause groundwater levels to fall continuously for long periods of time, even if yearly abstractions remain below the average replenishment rate. Recharge is naturally difficult to quantify, as it depends on a complex variety of factors. Indirect techniques based on mathematical models have long since been advocated as valuable means to estimate recharge. This paper presents a methodology to estimate groundwater recharge in quick-response semiarid karst aquifers. Lumped and distributed models are used to evaluate the fraction of rainfall that ultimately results in aquifer recharge, as well as the correlation between the magnitude of rainfall events and infiltration rates. Modelling results are then compared with direct observations of the recharge processes and discussed to evaluate the implications of time scales. This study is demonstrated through a case-specific application to the Ventós aquifer, an intensively exploited carbonate system located in one of the driest areas of peninsular Spain. Overall, both approaches perform similarly, although the lumped model exhibits a better agreement with field records. Results reflect the nonlinear nature of the rainfall/recharge ratio. The fraction of rainfall that ultimately recharges the aquifer seems to increase exponentially with the magnitude of the event. [Copyright &y& Elsevier]

Summary: Adequate assessment of uncertainty for prediction and simulation purposes is a current issue in hydrological research. This article describes the application of the Hydrologic Uncertainty Processor (HUP) proposed by Krzystofowicz in 1999 to a small semi-arid watershed in southern Italy. The version applied in this work is a precipitation-dependent HUP aimed at assessing the hydrologic uncertainty about actual streamflow at some future time, with lead times of a few hours, given the information available at the forecast time and assuming a perfectly known amount of precipitation. The processor is based on Bayes theorem and hence models the prior and likelihood functions to obtain the revised posterior distribution. A complete example of the modelling assumptions, estimation procedure and results is carried out in the present paper. In detail, we analysed a 26-km2 semi-arid basin, considering hourly forecasts over an almost continuous five-year period in 2000–2005. A distributed rainfall–runoff model suited to represent contributions of different runoff generation mechanisms to hydrologic response is used for deterministic predictions. Analysis of the resulting posterior distributions show that hydrologic uncertainty: (i) grows with the value of discharge predicted by the model; (ii) is higher when associated with high precipitation amounts; and (iii) increases with lead time of predictions. The predictive ability of the processor is investigated for several runoff events. The results indicate good processor performance for a lead time equal to the period covered by the precipitation forecast, and a significant deterioration for higher lead times that is heavily dominated by the presumption of null precipitation beyond the forecast period. Finally, the skill of the processor is assessed through a retrospective analysis in terms of the probability of detection and the false-alarm rate. [Copyright &y& Elsevier]

Summary: Dew is an important source of moisture for plants, biological soil crusts, invertebrates and small vertebrates in desert environments. In this paper, measurements were taken to investigate the effects of three different types of biological soil crusts (cyanobacteria, lichen and moss) and bare sand on dew deposition in the Gurbantunggut Desert. Dew quantities were measured using micro-lysimeters with a diameter of 6cm and a height of 3.5cm. The results showed that the total amount of dew deposited increased with the development of soil crusts, from bare sand to cyanobacterial crust to lichen crust to moss crust. The average amount of dew deposited daily on the moss crust was the highest of all and it was significant higher than the other three soil surfaces (lichen crust, cyanobacterial crust and bare sand) (p <0.05). During the period of the study, for each type of crust studied, the maximum amount of dew recorded was several times greater than the minimum. Moss crust was characterized by having the greatest amount of dew at dawn and also the maximum amount of dew deposited, whereas bare sand yielded the lowest amount of dew, with lichen crust and cyanobacterial crust exhibiting intermediate values. However, this was not the case for dew duration, as bare sand retained moisture for the longest period of time, followed by cyanobacterial crust, moss crust and finally lichen crust. Dew continued to condense even after sunrise. Furthermore, the differences in dew deposition may be partially attributed to an effect of the biological soil crusts on surface area. This study demonstrates the important effect of biological soil crusts upon dew deposition and may assist in evaluating the role of dew in arid and semi-arid environments. [Copyright &y& Elsevier]

• Evaluated 14 regionalization methods with four hydrological models in 3444 catchments. • Keeping poorly calibrated gauged catchments is preferable in poorly gauged regions. • The rank of different regionalization methods is similar among different climatic regions and hydrological models. Over recent decades, hydrologists have proposed a variety of methods to predict discharge in ungauged catchments, and significant progress has been made in the field of hydrological model parameter regionalization. However, uncertainties from both hydrological models and regionalization methods make it a challenge to draw clear conclusions for some questions in regionalization (e.g., the best performing regionalization method, the optimal number of donor catchments, and the optimal efficiency threshold of donor catchments). In this study, for the first time, we made an attempt to address such questions in one paper through a comprehensive evaluation of model performance by using five regionalization methods with two weighting schemes, two averaging options, five efficiency thresholds, and four lumped hydrological models over a broad set of 3444 catchments under varying hydroclimatic conditions in North America. The results show that: (1) Spatial Proximity with the Inverse Distance Weighting method and the output average option (SPI-out) generally performs better than or comparable to other regionalization methods for different climate regions and hydrological models, while the global mean method performs the worst. (2) The rank of different regionalization methods is similar among different climatic regions and hydrological models. Compared to catchments with other climates, regionalization methods perform worst in the arid regions. (3) The selection of five donors is relatively efficient for distance/attributes-based regionalization approaches with the output averaging option disregarding the efficiency threshold. (4) The differences of median Kling-Gupta efficiency values among thresholds of "all", 0.6 and 0.7 are no more than 0.05 for each regionalization method. However, the regionalization performance significantly deteriorates from using efficiency thresholds of 0.7 to 0.9 due to the significant reduction of available donor catchments. Thus, the poorly calibrated catchments may need to be included in the regionalization process, especially when the number of catchments is insufficient. [ABSTRACT FROM AUTHOR]

Summary: The paper presents an application of NOAA-AVHRR and GRACE data for studying the regional hydrogeology of the Quaternary aquifer in the Lake Chad basin. The actual evapotranspiration (ET) over the phreatic aquifer is computed using the S-SEBI algorithm and then compared to the ET estimates derived from the GRACE land water solutions. Both the GRACE solutions and the S-SEBI results are similar in description of the actual ET over the Lake Chad basin. AVHRR data helped to overcome non-uniqueness in the modelling of the piezometry anomalies. Particularly, in regional groundwater models, the Harr piezometric dome appeared to be an area of relatively high effective recharge, while the Chari-Baguirmi and the Kadzell piezometric depressions and Bahr-el-Gahzal were probably areas of excess ET over recharge. [Copyright &y& Elsevier]

Abstract: Here, an investigation has been carried out in order to understand the influence of the surface roughness in the definition of the hydrological response of semiarid catchments. Following a previous study of one of the authors, a modified version of TOPMODEL is used, in which the convolution routing procedure has been extended to the hillslopes by specifying the routing velocity for each pixel of the watershed. These velocities have been linked to the watershed land use through the different surface roughness whose coefficients has been derived on the basis of Engman''s table. In this paper, roughness coefficient distributions are expressed as function of a unique value treated as a calibration parameter. An analysis of model response in terms of prediction has been made for each roughness coefficient distributions using the GLUE procedure. Results from the application of the modified version of TOPMODEL in a Mediterranean experimental catchment located in Sicily are presented and discussed. [Copyright &y& Elsevier]

The spatial variability of landscape features such as topography, soils and vegetation defines the spatial pattern of hydrological state variables like soil moisture. Spatial variability thereby controls the functional behaviour of the landscape in terms of its runoff response. A consequence of spatial variability is that exchange processes between landscape patches can occur at various spatial scales ranging from the plot to the basin scale. In semi-arid areas, the lateral redistribution of surface runoff between adjacent landscape patches is an important process. For applications to large river basins of 104–105 km2 in size, a multi-scale landscape discretization scheme is presented in this paper. The landscape is sub-divided into modelling units within a hierarchy of spatial scale levels. By delineating areas characterized by a typical toposequence, organised and random variability of landscape characteristics is captured in the model. Using runoff–runon relationships with transition frequencies based on areal fractions of modelling units, lateral surface and subsurface water fluxes between modelling units at the hillslope scale are represented. Thus, the new approach allows for a manageable description of interactions between fine-scale landscape features for inclusion in coarse-scale models. Model applications for the State of Ceará (148,000 km2) in the north-east of Brazil demonstrate the importance of taking into account landscape variability and interactions between landscape patches in a semi-arid environment. Using mean landscape characteristics leads to a considerable underestimation of infiltration-excess surface runoff and total simulated runoff. Re-infiltration of surface runoff and lateral redistribution processes between landscape patches cause a reduction of runoff volumes at the basin scale and contribute to the amplification of variations in runoff volumes relative to variations in rainfall volumes for semi-arid areas. [Copyright &y& Elsevier]

• Water use strategies of Salix was quantified at each growth stage. • Root water uptake processes and water stress with two water table depths was found. • Interaction among atmospheric, soil water, groundwater and vegetation is emphasized. Soil water and groundwater are important water resources for vegetation survival and growth in arid and semiarid regions, and their contributions to water use over a whole growth period are difficult to quantify with limited observations. Additionally, the root water uptake (RWU) processes of groundwater-dependent xeric vegetation are specific and aggravate the complexity of these issues. In this paper, Salix is selected to study the interaction among atmosphere, soil water, groundwater, and RWU from the sprout to withered stage based on an observation within the ' In situ Monitoring Lysimeter System of the Atmosphere-Plant-Unsaturated Zone-Groundwater Continuum'. Two lysimeters with a diameter of 2 m and depths of 1.2 m and 4.2 m were implemented with Salix. The initial water table depth was 0.7 m in case 1 and 2.2 m in case 2. The results show that: Water use of Salix is the main contribution to actual evapotranspiration (ETa), no less than 80%. ETa was 462.75 mm in case 1 with a shallower soil layer and limited groundwater, during the entire growth period, 2016. Contrastively, it was 619.70 mm in case 2 with relatively abundant soil water and groundwater. The soil water and groundwater contribution were 89.6% and 10.4%, 74.3% and 25.7% for both cases. The selective water use by Salix in different soil layers was subject to temporal moisture availability. Salix extended to utilize groundwater in drought period and shifted back to wetter upper layers in case of rainfall. The access to groundwater significantly alleviates water stress, although rainfall replenishment can also play a part. Salix can not only intercept rainfall infiltration in the root zone, but also cause the decrease of water level, implying that the replanting of Salix should be carried out in a reasonable mode to ensure rainfall infiltration and reduce the ineffective loss of groundwater. Our results provide a practical reference for groundwater management and ecology restoration in semiarid desert regions. [ABSTRACT FROM AUTHOR]

• An ET assimilation system (LPJ-SM A) is proposed suitable for water-limited areas. • LPJ-SM A couples the LPJ-DGVM model with the PT-JPL SM scheme. • Microwave remote sensing soil data SMAP is used. • The application of SMAP data improves the accuracy of the coupled ET simulation. • The spatial results of LPJ-SM A has greatest similarity to NLDAS-2 ET product with continental-scale. An accurate estimation of evapotranspiration (ET) is essential for characterizing the water budget in arid and semiarid ecosystems. Although various soil moisture data have been used to improve the hydrological process modeling, only a few studies improved ET estimation at a global scale by utilizing satellite soil moisture active passive SMAP data, particularly targeting arid and semiarid areas. To address this issue, this paper proposes a process-based assimilation scheme (LPJ-SM A) to simulate daily ET at 0.25° spatial resolution for the water limited areas. First, an integrated model (LPJ-PM) is constructed by the updated Priestley–Taylor Jet Propulsion Laboratory model (PT-JPL SM) and the Lund-Potsdam-Jena Dynamic Global Vegetation Model (LPJ-DGVM). As the PT-JPL SM model establishes a connection between soil moisture (SM) and ET, the SMAP data could be integrated into LPJ-PM. Second, with the estimated ET PM (3-day interval) in LPJ-PM as "observations", the original ET LPJ (daily) estimated by LPJ-DGVM could be well constrained in a water-limited area through data assimilation. The results showed that: (1) the ET PM with SMAP information performed better and had a higher accuracy than ET LPJ. (2) After assimilating ET PM into LPJ-DGVM, the assimilated-ET (ET DA) showed a superior performance (R = 0.75, RMSD = 0.72 mm/d) to ET LPJ (R = 0.55, RMSD = 1.02 mm/d) and ET PM (R = 0.70, RMSD = 0.93 mm/d) when evaluated against in situ observations at a 95% significance level. Our proposed assimilation system (LPJ-SM A) was applied to arid and semiarid regions in the United States, and the results illustrate that the spatial distribution and annual value of the LPJ-SM A ET was very similar to NLDAS-2 ET products, which have a higher precision over North America than other global 'reference' products. The proposed LPJ-SM A system can be used to optimize model simulation performance and effectively improve ET prediction accuracy. This method can be used as an alternative to estimate global ET, especially in water-limited regions. [ABSTRACT FROM AUTHOR]

• Replenishment activities significantly impact lake evolution. • We highlight the contributions of groundwater and chemical reactions in lake salinity reduction. • Virtual sample is introduced in NETPATH hydrogeochemical model for lake. • High quality and large volume replenishment water will help rehabilitate lake ecosystem. • Results could be useful to promote sustainable lake water management in arid areas. Lakes in arid regions are ecologically valuable yet highly fragile due to intense evaporation. To provide an extra water supply for maintaining water balance in lakes, the Ecological Replenishment Water Program (ERWP) in northwest China has significantly changed the hydrological and hydrochemical conditions for these lakes. Descriptive statistics and water and mass balances, together with hydrogeochemical modeling were used in this study to gain an understanding of the impacts of water replenishment (irrigation and drainage water) on evolution for Shahu Lake. A virtual sample was introduced in NETPATH hydrogeochemical modeling to compute the net chemical reactions in the lake water. Variations in TDS indicated that the lake evolved to be saline during 2004–2012 (stage I) and then tended to be fresh during 2013–2014 (stage II). Results highlighted that groundwater outflow and chemical reactions were the overriding factors controlling chemical evolution in the lake system, which greatly depend on the replenishment activities. The salinity reduction from the virtual samples to the final samples were attributed to the precipitation of calcite and dolomite, dissolution of gypsum, Na-K and Na-Ca exchange, and the CO 2 degassing in the lake system at an annual scale of 0.11 g/L in stage I and 0.15 g/L in stage II. The quality of replenishment water was as important as quantity for rehabilitating lakes, as it significantly determines the occurrence of chemical reactions in lake water. Findings from this paper can provide insight into the evolution of arid lakes in response to replenishment activities and can help contribute to better management of a valuable and fragile resource. [ABSTRACT FROM AUTHOR]

• Present a watershed pollution load model (HIMS–PL model) for semiarid and semihumid areas. • Analyze the sensitivity of HIMS–PL model. • Check the suitability of HIMS–PL model for simulations of streamflow, sediment and pollution load in semiarid and semihumid catchments. Modeling pollutant processes in soil and water is helpful to better understand a pollutant's potential adverse impacts on an environmental system. There are many watershed pollution load models; however, their effectivity is generally poor in semiarid and semihumid areas because of the complexity of hydrological processes and pollutant transport processes. In this paper, a pollution load module was combined with the well-established HIMS (Hydro-Informatic Modelling System) model for the purpose of simulating the processes of pollution generation and transport and quantifying the pollution load in semiarid and semihumid areas. The model has the advantages of a simple structure and low data requirement, and can simulate dissolved and solid-phase nitrogen and phosphorus. As a demonstration, the HIMS-pollution load (HIMS-PL) model was respectively tested for three semiarid and semihumid basins in China—the Liuhe and the Yixunhe River basins, two sub-basins of the Luanhe River basin, and the Chaohe River basin. Model simulations of streamflow and pollution loads at monthly time step accurately matched the observed streamflow (with NSEs 0.77–0.95 and REs 0.53–11.24%) and pollution load (with NSEs 0.54–0.83 and REs 2.45–12.72% for total nitrogen loads and with NSEs 0.51–0.79 and REs 2.22–19.70% for total phosphorus loads). In comparison with HSPF and GWLF models, the HIMS-PL model performed better than the GWLF model in all of the above-mentioned basins and better than the HSPF model in some of the basins. Overall, the proposed model is generally suitable for simulating streamflow and pollution load in semiarid and semihumid regions. [ABSTRACT FROM AUTHOR]