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Flow regulation and irrigation alter local freshwater conditions, but their global effects are highly uncertain. We investigated these global effects from 1901 to 2008, using hydroclimatic observations in 100 large hydrological basins. Globally, we find consistent and dominant effects of increasing relative evapotranspiration from both activities, and decreasing temporal runoff variability from flow regulation. The evapotranspiration effect increases the long-term average human consumption of fresh water by 3563 ± 979 km(3)/year from 1901-1954 to 1955-2008. This increase raises a recent estimate of the current global water footprint of humanity by around 18%, to 10,688 ± 979 km(3)/year. The results highlight the global impact of local water-use activities and call for their relevant account in Earth system modeling., (Copyright © 2015, American Association for the Advancement of Science.)

This perspective paper argues for an urgent need to monitor a set of 12 concrete, measurable indicators of food and water security in the Arctic over time. Such a quantitative indicator approach may be viewed as representing a reductionist rather than a holistic perspective, but is nevertheless necessary for actually knowing what reality aspects to monitor in order to accurately understand, quantify, and be able to project critical changes to food and water security of both indigenous and non-indigenous people in the Arctic. More relevant indicators may be developed in the future, taking us further toward reconciliation between reductionist and holistic approaches to change assessment and understanding. However, the potential of such further development to improved holistic change assessment is not an argument not to urgently start to monitor and quantify the changes in food and water security indicators that are immediately available and adequate for the Arctic context.

The goals for water-quality and ecosystem integrity are often defined relative to "natural" reference conditions in many water-management systems, including the European Union Water Framework Directive. This paper examines the difficulties created for water management by using "natural" as the goal. These difficulties are articulated from different perspectives in an informal (fictional) conversation that takes place after a workshop on reference conditions in water-resources management. The difficulties include defining the natural state and modeling how a system might be progressed toward the natural, as well as the feasibility and desirability of restoring a natural state. The paper also considers the appropriateness for developing countries to adopt the use of natural as the goal for water management. We conclude that failure to critically examine the complexities of having "natural" as the goal will compromise the ability to manage the issues that arise in real basins by not making the ambiguities associated with this "natural" goal explicit. This is unfortunate both for the western world that has embraced this model of "natural as the goal" and for the developing world in so far as they are encouraged to adopt this model.

Environmental policies for water quality and ecosystem management do not commonly require explicit stochastic accounts of uncertainty and risk associated with the quantification and prediction of waterborne pollutant loads and abatement effects. In this study, we formulate and investigate a possible environmental policy that does require an explicit stochastic uncertainty account. We compare both the environmental and economic resource allocation performance of such an uncertainty-accounting environmental policy with that of deterministic, risk-prone and risk-averse environmental policies under a range of different hypothetical, yet still possible, scenarios. The comparison indicates that a stochastic uncertainty-accounting policy may perform better than deterministic policies over a range of different scenarios. Even in the absence of reliable site-specific data, reported literature values appear to be useful for such a stochastic account of uncertainty.

Human water use and anthropogenic water pollution and ecosystem deterioration have increased so much that it is now a strategic challenge to maximize benefits from various possible water uses, while ensuring that basic human needs are met and the environment is protected. We propose and develop a novel use of input-output flow analysis as a relatively simple, compact and powerful tool for quantification of coupled natural and cross-sectoral flows of water, nutrients, and pollutants in catchments. The tool quantifies implications of various environmental regulation and management scenarios for both natural water systems and engineered-economic systems and sectors that use and impact natural waters for meeting human needs. Specific case study application to water and nitrogen flows in the Swedish Norrström drainage basin indicates considerable nitrogen load contributions to surface and coastal waters from slow groundwater flow paths and legacies of accumulated nitrogen in subsurface and immobile water pools. This implies that effective nitrogen load abatement cannot focus only on active sources but must also include downstream measures, which can capture and abate nitrogen/pollutant loading from different types of known and yet unknown point and diffuse sources within associated catchments.

The article titled "Thank You to Our 2023 Reviewers" expresses gratitude to the individuals who reviewed manuscripts for the journal Water Resources Research (WRR) in 2023. The efforts of these reviewers have contributed to the high quality and impact of the journal's papers and the overall research in the field of water science. In total, 2,809 individuals provided 4,453 peer reviews, with 354 individuals reviewing three or more papers. The editors, associate editors, and authors of WRR sincerely thank all the reviewers and anticipate the publication of exciting advances in 2024. [Extracted from the article]

Translational research (TR) represents a promising systematic process for going from scientific discoveries to practical applications. Through conversations with academics, practitioners, decision‐makers and users, there has emerged a broad level of water science community support for including TR in Water Resources Research (WRR) publications. Based on this, we now open a continuing special collection of TR papers in WRR. The aim is to facilitate a community within hydrology and water science that seeks to provide actionable knowledge for societal benefit across disciplines, scales and contexts, with a focus on water as a key societal resource or a risk (e.g., of floods, droughts, or as pollutant carrier). This Editorial discusses what the multi‐faceted nature of TR may include in the context of WRR, why it is important to encourage TR papers in WRR, and how the opening of a continuing special collection of translational water research papers initiates a process to include such articles in the journal. Key Points: Opening a continuing special collection for translational research (TR) papers in the context of Water Resources Research (WRR)Explaining the multi‐faceted nature of TR and Initiating a process to encourage and include such papers in WRRAiming to facilitate a community within hydrology and water science that seeks to provide actionable knowledge for societal benefit [ABSTRACT FROM AUTHOR]

Population growth is increasing the pressure on water resource availability. For useful assessment and planning for societal water availability impacts, it is imperative to disentangle the direct influences of human activities in the landscape from external climate‐driven influences on water flows and their variation and change. In this study we used the water balance model, a gridded global hydrological model, to quantify and distinguish human‐driven change components, modified by interventions such as dams, reservoirs, and water withdrawals for irrigation, industry, and households, from climate‐driven change components on four key water balance variables in the terrestrial hydrological system (evapotranspiration, runoff, soil moisture, storage change). We also analyzed emergent effect patterns in and across different parts of the world, facilitating exploration of spatial variability and regional patterns on multiple spatial scales, from pixel to global, including previously uninvestigated parts of the world. Our results show that human activities drive changes in all hydrological variables, with different magnitudes and directions depending on geographical location. The differences between model scenarios with and without human activities were largest in regions with the highest population densities. In such regions, which also have relatively large numbers of dams for irrigation, water largely tends to be removed from storage and go to feed increased runoff and evapotranspiration fluxes. Our analysis considers a more complete set of hydrological variables than previous studies and can guide further research and management planning for future hydrological and water availability trends, including in relatively data‐poor parts of the world. Plain Language Summary: The global population is growing, increasing demands for water use. Knowledge of how human activities affect water resources is available for some areas and water cycle components, but more data are needed for solid scientific understanding of climate and human‐driven effects on water resources in the past and present, and to underpin management approaches to future trends in hydrology and water availability. This study examined human activity effects on different components of the terrestrial water cycle, distinct from the effects of climate change. Results showed that human activities alter movements of water worldwide, with changes, magnitudes, and directions depending on world region. The greatest human‐driven changes emerged in regions with the highest population density, which also have relatively large numbers of dams providing water for agricultural use. Overall, the water changes in these regions tend to include water removal from storage going to feed increased evapotranspiration and/or runoff. Regions with such change trends will require solutions to overcome future negative impacts on society and ecosystems. This study showed how different water cycle components and land regions have been affected by changes in human activities, and findings can guide research and management planning for hydrological and water availability in future years. Key Points: Human activities affected all four hydrological variables studied (runoff, evapotranspiration, soil moisture, and storage change)Human‐driven hydrological effects emerged as considerable over the northern tropical to temperate latitudes, where most people liveHigher runoff was seen in areas with dams of various types, with additional hydrological effects depending on dam type [ABSTRACT FROM AUTHOR]

On behalf of the editorial board of Water Resources Research (WRR) and the entire water science community, we want to express our most heartfelt gratitude to all who reviewed manuscripts for the journal in 2021. Your great efforts have ensured and improved the high quality and impact of the WRR papers and generally of research in our field. In 2021, the 2,960 individuals listed below have contributed 4,788 peer reviews with the 432 people indicated in italics, reviewing three or more papers for the journal. The editors, associate editors, and authors of WRR sincerely thank all our reviewers and look forward to the exciting advances that will be published in WRR in 2022. [ABSTRACT FROM AUTHOR]

Coastal wetlands and lagoons are under pressure due to competing demands for freshwater resources and climatic changes, which may increase salinity and cause a loss of ecological functions. These pressures are particularly high in Mediterranean regions with high evaporative demand compared to precipitation. To manage such wetlands and maximize their provision of ecosystem services, their hydrologic balance must be quantified. However, multiple channels, diffuse surface water exchanges, and diverse groundwater pathways complicate the quantification of different water balance components. To overcome this difficulty, we developed a mass balance approach based on coupled water and salt balance equations to estimate currently unknown water exchange fluxes through the Gialova lagoon, southwestern Peloponnese, Greece. Our approach facilitates quantification of both saline and freshwater exchange fluxes, using measured precipitation, water depth and salinity, and estimated evaporation rates over a study period of 2 years (2016–2017). While water exchanges were dominated by evaporation and saline water inputs from the sea during the summer, precipitation and freshwater inputs were more important during the winter. About 40 % and 60 % of the freshwater inputs were from precipitation and lateral freshwater flows, respectively. Approximately 70 % of the outputs was due to evaporation, with the remaining 30 % being water flow from the lagoon to the sea. Under future drier and warmer conditions, salinity in the lagoon is expected to increase, unless freshwater inputs are enhanced by restoring hydrologic connectivity between the lagoon and the surrounding freshwater bodies. This restoration strategy would be fundamental to stabilizing the current wide seasonal fluctuations in salinity and maintain ecosystem functionality but could be challenging to implement due to expected reductions in water availability in the freshwater bodies supporting the lagoon. [ABSTRACT FROM AUTHOR]

Comprehensive assessment of hydro-climatic variations and change trends is essential for understanding, mitigating, and adapting to key water resource changes in different parts of the world. We performed such an assessment on Iran, as representative of an arid/semi-arid and geopolitically important world region. We acquired and calculated data time series of surface temperature (T), precipitation (P), runoff (R), evapotranspiration (ET), and water storage change (DS), to determine their status and changes in and among the 30 main hydrological basins in Iran over the period 1986–2016. From 1986–2000 to 2001–2016, the country warmed, P mostly decreased and R even more so, while water storage was depleted (DS < 0) and ET increased in some basins. Overall, the extra water provided from primarily groundwater depletion has fed and kept ET at levels beyond those sustained by the annually renewable water input from P. This indicates unsustainable use of water for maintaining and expanding human activities, such as irrigated agriculture, in this part of the world. [ABSTRACT FROM AUTHOR]

Surface water bodies and their changes in the landscape are critical for societies and ecosystems. However, the global change in surface water area over the last decades remains unclear, as recent studies using the same satellite data disagree on its direction. Here, we reanalyze reported maps of global water classification based on that data in order to estimate the changes in long‐term average surface water area from the first (1985–2000) to the second (2001–2015) half of the recent 30‐year period (1985–2015). We find a net gain in global surface water area by 100,454 km2, primarily due to seasonal water gains (83,329 km2). Over the world, we identify net wetting in 187 and net drying in 57 regional hydrological catchments, with the greatest water gain in Sabarmati (India) and loss in Amu Darya (Uzbekistan). We provide an interactive map to further explore the highly heterogeneous local changes around the world. Plain Language Summary: The surface water resources over the world's continental area are critical for water security, ecosystem functioning, hydroclimatic regulation, and related societal functions. To resolve contrasting reports on how global surface water area has changed over the last decades, we have reanalyzed the underlying data from satellite observations over the period 1985–2015. We find that the world's surface water area has increased from the first to the second half of that period, and this net global wetting has been mainly due to seasonal water gains. Permanent surface water area has also increased but considerably less than the seasonal gains, and there are also some major local drying exceptions, like the Aral Sea in Central Asia and Lake Urmia in Iran. Most commonly, the local surface water changes have been heterogeneous, with relatively small distances between wetting and drying occurrences, and we provide an interactive map for further exploration and visualization of these changes around the world. Our results are important for freshwater resource and ecosystem management, planning, and adaptation and call for further research on the drivers and processes that determine seasonal and permanent water changes and their distributions in and among different world regions. Key Points: Contrasting findings are reported for changes in global surface water area over the last decadesThis study finds a net gain in global surface water area from 1985–2000 to 2001–2015Most of the world's regional hydrological catchments have gained surface water area, primarily by increased seasonal water cover [ABSTRACT FROM AUTHOR]

Rapid changes to the Arctic hydrological cycle challenge both our process understanding and our ability to find appropriate adaptation strategies. We have investigated the relevance and accuracy development of climate change projections for assessment of water cycle changes in major Arctic drainage basins. Results show relatively good agreement of climate model projections with observed temperature changes, but high model inaccuracy relative to available observation data for precipitation changes. Direct observations further show systematically larger (smaller) runoff than precipitation increases (decreases). This result is partly attributable to uncertainties and systematic bias in precipitation observations, but still indicates that some of the observed increase in Arctic river runoff is due to water storage changes, for example melting permafrost and/or groundwater storage changes, within the drainage basins. Such causes of runoff change affect sea level, in addition to ocean salinity, and inland water resources, ecosystems, and infrastructure. Process-based hydrological modeling and observations, which can resolve changes in evapotranspiration, and groundwater and permafrost storage at and below river basin scales, are needed in order to accurately interpret and translate climate-driven precipitation changes to changes in freshwater cycling and runoff. In contrast to this need, our results show that the density of Arctic runoff monitoring has become increasingly biased and less relevant by decreasing most and being lowest in river basins with the largest expected climatic changes. [ABSTRACT FROM AUTHOR]

Changes in subsurface water resources might alter the surrounding ground by generating subsidence or uplift, depending on geological and hydrogeological site characteristics. Improved understanding of the relationships between surface water storage and ground deformation is important for design and maintenance of hydraulic facilities and ground stability. Here, we construct one of the longest series of Interferometric Synthetic Aperture Radar (InSAR) to date, over twenty-five years, to study the relationships between water level changes and ground surface deformation in the surroundings of Lake Mead, United States, and at the site of the Hoover Dam. We use the Small Baseline Subset (SBAS) and Permanent scatterer interferometry (PSI) techniques over 177 SAR data, encompassing different SAR sensors including ERS1/2, Envisat, ALOS (PALSAR), and Sentinel-1(S1). We perform a cross-sensor examination of the relationship between water level changes and ground displacement. We found a negative relationship between water level change and ground deformation around the reservoir that was consistent across all sensors. The negative relationship was evident from the long-term changes in water level and deformation occurring from 1995 to 2014, and also from the intra-annual oscillations of the later period, 2014 to 2019, both around the reservoir and at the dam. These results suggest an elastic response of the ground surface to changes in water storage in the reservoir, both at the dam site and around the reservoir. Our study illustrates how InSAR-derived ground deformations can be consistent in time across sensors, showing the potential of detecting longer time-series of ground deformation. [ABSTRACT FROM AUTHOR]

Understanding the partitioning of precipitation water among different water fluxes and storage changes in the landscape, and the co-variations of these variables under various hydroclimatic conditions is essential for quantification and management of water resources and climate feedbacks. This study analyses the co-variation of temperature, precipitation, evapotranspiration, runoff and soil moisture anomalies based on data from two alternative sets of global observational and re-analysis products for 1378 catchments across three separate climate regions of Europe over the period 1980-2010. Co-variation details depend on both climatic zone and which of the alternative datasets is used for the analysis. However, consistently across all climate regions and both alternative datasets, the results show stronger correlation of soil moisture and runoff anomalies, than of the former and any of the other studied hydroclimatic variable anomalies. The latter findings of weak correlations include those of soil moisture with precipitation and evapotranspiration anomalies, even though the latter two hydroclimatic variables are commonly considered as most closely linked with soil moisture. The strong correlation between soil moisture and runoff also applies under extreme event occurrences for both wet and dry conditions, with the co-occurrences of extreme soil moisture and precipitation or evapotranspiration events being considerably less well linked. These results indicate soil moisture variations and associated closely linked groundwater table variations as key regulators of runoff variations, through changes in subsurface hydraulic gradients and associated groundwater flows into streams. In contrast, soil moisture and groundwater level variations do not co-vary as much and/or as quickly with precipitation and evapotranspiration anomalies because precipitation may primarily regulate evapotranspiration and, even under no precipitation conditions, there often still remains enough soil water available for the vegetation to keep transpiring and thus maintaining a relatively high evapotranspiration level. Overall, the results of this study emphasize the complex water flux and storage change connections by transport of both water-mass/volume and water-pressure though whole-catchment pathways, including their subsurface water parts, of various lengths. While the transport of water-mass/volume is slow and may take long time over long pathway distances, such as from many parts of the land surface (where precipitation and evapotranspiration act) to nearest stream (where runoff is observed), the groundwater table (i.e., groundwater pressure) and linked soil moisture (and soil water pressure) variations are faster and lead to quick and strong hydraulic gradient and associated runoff change responses along the entire stretches of short and long water pathways. These fast pressure response connections explain the strong correlations found consistently between soil moisture and runoff anomalies in this comprehensive multi-catchment and multi-climate study. [ABSTRACT FROM AUTHOR]

Understanding the climatic and direct human drivers of abrupt drying of lakes in many parts of the world is a high research priority, particularly for water resources management and restoration. Lake Urmia, a shallow endemic lake in north-west Iran and one of the major saltwater bodies on earth, has undergone a dramatic decline in its water level (WL) in the past decades, resulting in about 80% of loss in the lake's water content. Different explanations have been discussed regarding the primary cause of this WL decline, including climate change, and regional human-driven land- and water-use changes. This paper reports a comprehensive study of the possible primary drivers of the lake's desiccation. Using classical exploratory statistical methods, the analysis accounts for the relationships between climate change (precipitation P, temperature T), land-surface and hydrological evolution (soil moisture SM, and WL), and vegetation cover (VC) change in the region. The latter includes human-driven changes of irrigation and expansion of agricultural lands. Observations over the period 1981-2015 indicate that the observed variability in P, T, and SM cannot explain the sharp decline in the lake WL since 2000. Instead, land-surface analysis shows VC was nearly doubled after 2000 in the Lake Urmia watershed, indicating that the WL decline is mainly associated with human-driven agricultural increase of VC. The expansion of agricultural activities in the watershed has led to increasing transpiration and hence, total evapotranspiration, decreasing the runoff during the increase in VC (inherently including irrigation, storage, and water diversion). Our results are consistent with similar cases around the world identifying human activities and interventions as the main driver of hydrologic changes, while climate change will likely increasingly contribute to such changes and their impacts in the future. [ABSTRACT FROM AUTHOR]