Notable shifts beyond pre-industrial streamflow and soil moisture conditions transgress the planetary boundary for freshwater change

Human actions compromise the many life-supporting functions provided by the freshwater cycle. Yet, scientific understanding of anthropogenic freshwater change and its long-term evolution is limited. Here, using a multi-model ensemble of global hydrological models, we estimate how, over a 145-year industrial period (1861–2005), streamflow and soil moisture have deviated from pre-industrial baseline conditions (defined by 5th–95th percentiles, at 0.5° grid level and monthly timestep over 1661–1860). Comparing the two periods, we find an increased frequency of local deviations on ~45% of land area, mainly in regions under heavy direct or indirect human pressures. To estimate humanity’s aggregate impact on these two important elements of the freshwater cycle, we present the evolution of deviation occurrence at regional to global scales. Annually, local streamflow and soil moisture deviations now occur on 18.2% and 15.8% of global land area, respectively, which is 8.0 and 4.7 percentage points beyond the ~3 percentage point wide pre-industrial variability envelope. Our results signify a substantial shift from pre-industrial streamflow and soil moisture reference conditions to persistently increasing change. This indicates a transgression of the new planetary boundary for freshwater change, which is defined and quantified using our approach, calling for urgent actions to reduce human disturbance of the freshwater cycle

Global Assessment of Groundwater Stress Vis-à-Vis Sustainability of Irrigated Food Production

Due to poor water resources management, groundwater-dependent agriculture induces substantial stress on several aquifer systems worldwide, which poses a serious threat to water and food security. However, only a few studies have addressed this vital issue. This study aimed to evaluate stress on aquifers due to the overuse of groundwater for food production and explore pathways for stress reduction via improved irrigation efficiency and productivity. Groundwater stress was characterized using the ratio of water use to availability, with consideration for environmental flows. The results indicated that out of 107 countries—dependent on groundwater irrigation, about half are overexploiting groundwater, while one-fifth of these countries are extracting moderately-to heavily. Over 90% of the non-renewable groundwater abstraction occurs in 7 countries. Further, about 450 million tonnes (Mt) of global annual food production is from non-renewable groundwater exploitation. If the existing irrigation efficiency is increased to 90%, current groundwater stress would be reduced by 40%. Additionally, in unstressed regions, it would be possible to produce additional 300 Mt of food by using saved water while maintaining groundwater stress at acceptable levels. Moreover, improved water productivity in conjunction with increased irrigation efficiency could reduce the current level of unsustainable food production by 47%. These results provide important insights into the dynamics of irrigation stress on groundwater systems, and the role of managerial interventions

Predicting groundwater recharge for varying land cover and climate conditions - a global meta-study

Groundwater recharge is one of the important factors determining the groundwater development potential of an area. Even though recharge plays a key role in controlling groundwater system dynamics, much uncertainty remains regarding the relationships between groundwater recharge and its governing factors at a large scale. Therefore, this study aims to identify the most influential factors of groundwater recharge, and to develop an empirical model to estimate diffuse rainfall recharge at a global scale. Recharge estimates reported in the literature from various parts of the world (715 sites) were compiled and used in model building and testing exercises. Unlike conventional recharge estimates from water balance, this study used a multimodel inference approach and information theory to explain the relationship between groundwater recharge and influential factors, and to predict groundwater recharge at 0.5 degrees resolution. The results show that meteorological factors (precipitation and potential evapotranspiration) and vegetation factors (land use and land cover) had the most predictive power for recharge. According to the model, long-term global average annual recharge (1981-2014) was 134 mm yr(-1) with a prediction error ranging from -8 to 10 mm yr(-1) for 97.2% of cases. The recharge estimates presented in this study are unique and more reliable than the existing global groundwater recharge estimates because of the extensive validation carried out using both independent local estimates collated from the literature and national statistics from the Food and Agriculture Organization (FAO). In a water-scarce future driven by increased anthropogenic development, the results from this study will aid in making informed decisions about groundwater potential at a large scale

Not Available

Not AvailableIncreasing groundwater contamination across the globe triggered the concept of “aquifer vulnerability”, which has been extensively used worldwide during past three to four decades by researchers and policy makers for protecting groundwater from pollution. However, only a few recent studies have focused on the performance evaluation of two or more vulnerability assessment methods. Some of these studies have resulted in contrasting findings. Given this fact and considering growing threat of groundwater contamination due to increasing human activities across the globe, it is necessary to critically review existing methods, understand current research trends, and identify major challenges associated with the assessment of aquifer vulnerability. Hence, the aim of this study is to present a comprehensive review of the methods and approaches used for the evaluation of aquifer vulnerability for ‘resource’ and ‘source’ protection. First, the concept and types of aquifer vulnerability along with the definitions evolved over the years are presented, and then the methods for assessing aquifer vulnerability are suitably classified and briefly discussed. Second, the concept of vulnerability assessment for ‘source’ protection is highlighted, and the evolution of groundwater vulnerability evaluation methods is presented with an enlightening block diagram. Third, current research trends and critiques on past studies are discussed. Fourth, the major challenges of vulnerability assessment are highlighted and a way forward is suggested. It is concluded that the progress of vulnerability evaluation methods has not kept pace with the advancement of knowledge and tools/techniques. There is an urgent need for developing a scientifically robust and somewhat versatile methodology for the evaluation of ‘intrinsic’ and ‘specific’ groundwater vulnerability for ‘resource’ and ‘source’ protection under varying hydrogeologic and hydro-climatic conditions. It is emphasized that more studies should be devoted to vulnerability assessment for ‘source’ protection using ‘Source-Pathway-Receptor/Target’ approach. Also, spatial decision support systems should be developed using modern tools/techniques including artificial intelligence to improve decision-making process for protecting vital groundwater resources.Not Availabl

Global Assessment of Groundwater Stress Vis-à-Vis Sustainability of Irrigated Food Production

Due to poor water resources management, groundwater-dependent agriculture induces substantial stress on several aquifer systems worldwide, which poses a serious threat to water and food security. However, only a few studies have addressed this vital issue. This study aimed to evaluate stress on aquifers due to the overuse of groundwater for food production and explore pathways for stress reduction via improved irrigation efficiency and productivity. Groundwater stress was characterized using the ratio of water use to availability, with consideration for environmental flows. The results indicated that out of 107 countries—dependent on groundwater irrigation, about half are overexploiting groundwater, while one-fifth of these countries are extracting moderately-to heavily. Over 90% of the non-renewable groundwater abstraction occurs in 7 countries. Further, about 450 million tonnes (Mt) of global annual food production is from non-renewable groundwater exploitation. If the existing irrigation efficiency is increased to 90%, current groundwater stress would be reduced by 40%. Additionally, in unstressed regions, it would be possible to produce additional 300 Mt of food by using saved water while maintaining groundwater stress at acceptable levels. Moreover, improved water productivity in conjunction with increased irrigation efficiency could reduce the current level of unsustainable food production by 47%. These results provide important insights into the dynamics of irrigation stress on groundwater systems, and the role of managerial interventions

Poor correlation between large-scale environmental flow violations and freshwater biodiversity: implications for water resource management and the freshwater planetary boundary

| openaire: EC/HE/819202/EU//SOS.aquaterra Funding Information: This research has been supported by the Canada First Research Excellence Fund (grant no. C150-2017-8). Funding Information: The authors acknowledge various funds that made this research possible. Chinchu Mohan received funding from the Canada First Research Excellence Fund (CFRE); Matti Kummu received funding from the Academy of Finland funded project WATVUL (grant no. 317320), the Academy of Finland funded project TREFORM (grant no. 339834), and the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement no. 819202). Vili Virkki received funding from the Aalto University School of Engineering Doctoral Program and the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement no. 819202). Sonja C. Jähnig acknowledges funding through the Leibniz Association for the project Freshwater Megafauna Futures. Miina Porkka received funding from European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement no. 819202). Lan Wang-Erlandsson was supported by the European Research Council through the “Earth Resilience in the Anthropocene” project (grant no. ERC-2016-ADG 743080) and by the IKEA Foundation. Publisher Copyright: © Copyright:The freshwater ecosystems around the world are degrading, such that maintaining environmental flow Environmental flow (EF): "The quantity, timing, and quality of water flows required to sustain freshwater and estuarine ecosystems and the human livelihoods and well-being that depend on these ecosystems."- Arthington et al. (2018). (EF) in river networks is critical to their preservation. The relationship between streamflow alterations (subsequent EF violationsEF violations are deviations in streamflow beyond the upper and lower boundaries of environmental flow envelopes (EFEs). The EFEs establish an envelope for acceptable EF deviations based on pre-industrial (1801-1860) stream discharge (see Sect. 2.2 for more details)) and the freshwater biodiversity response is well established at the scale of stream reaches or small basins (g 1/4<100g km2). However, it is unclear if this relationship is robust at larger scales, even though there are large-scale initiatives to legalize the EF requirement. Moreover, EFs have been used in assessing a planetary boundaryPlanetary boundary: planetary boundary defines biogeophysical planetary-scale boundaries for Earth system processes that, if violated, can irretrievably impair the Holocene-like stability of the Earth system. for freshwater. Therefore, this study intends to conduct an exploratory evaluation of the relationship between EF violation and freshwater biodiversity at globally aggregated scales and for freshwater ecoregions. Four EF violation indices (severity, frequency, probability of shifting to a violated state, and probability of staying violated) and seven independent freshwater biodiversity indicators (calculated from observed biota data) were used for correlation analysis. No statistically significant negative relationship between EF violation and freshwater biodiversity was found at global or ecoregion scales. These findings imply the need for a holistic bio-geo-hydro-physical approach in determining the environmental flows. While our results thus suggest that streamflow and EF may not be the only determinant of freshwater biodiversity at large scales, they do not preclude the existence of relationships at smaller scales or with more holistic EF methods (e.g., including water temperature, water quality, intermittency, connectivity, etc.) or with other biodiversity data or metrics.Peer reviewe

Globally widespread and increasing violations of environmental flow envelopes

Human actions and climate change have drastically altered river flows across the world, resulting in adverse effects on riverine ecosystems. Environmental flows (EFs) have emerged as a prominent tool for safeguarding the riverine ecosystems, but at the global scale, the assessment of EFs is associated with high uncertainty related to the hydrological data and EF methods employed. Here, we present a novel, in-depth global EF assessment using environmental flow envelopes (EFEs). Sub-basin-specific EFEs are determined for approximately 4400 sub-basins at a monthly time resolution, and their derivation considers the methodological uncertainties related to global-scale EF studies. In addition to a lower bound of discharge based on existing EF methods, we introduce an upper bound of discharge in the EFE. This upper bound enables areas to be identified where streamflow has substantially increased above natural levels. Further, instead of only showing whether EFs are violated over a time period, we quantify, for the first time, the frequency, severity, and trends of EFE violations during the recent historical period. Discharge was derived from global hydrological model outputs from the ISIMIP 2b ensemble. We use pre-industrial (1801-1860) quasi-natural discharge together with a suite of hydrological EF methods to estimate the EFEs. We then compare the EFEs with recent historical (1976-2005) discharge to assess the violations of the EFE. These violations most commonly manifest as insufficient streamflow during the low-flow season, with fewer violations during the intermediate-flow season, and only a few violations during the high-flow season. The EFE violations are widespread and occur in half of the sub-basins of the world during more than 5% of the months between 1976 and 2005, which is double compared with the pre-industrial period. The trends in EFE violations have mainly been increasing, which will likely continue in the future with the projected hydroclimatic changes and increases in anthropogenic water use. Indications of increased upper extreme streamflow through EFE upper bound violations are relatively scarce and dispersed. Although local fine-tuning is necessary for practical applications, and further research on the coupling between quantitative discharge and riverine ecosystem responses at the global scale is required, the EFEs provide a quick and globally robust way of determining environmental flow allocations at the sub-basin scale to inform global research and policies on water resources management

Globally widespread and increasing violations of environmental flow envelopes

Human actions and climate change have drastically altered river flows across the world, resulting in adverse effects on riverine ecosystems. Environmental flows (EFs) have emerged as a prominent tool for safeguarding the riverine ecosystems, but at the global scale, the assessment of EFs is associated with high uncertainty related to the hydrological data and EF methods employed. Here, we present a novel, in-depth global EF assessment using environmental flow envelopes (EFEs). Sub-basin-specific EFEs are determined for approximately 4400 sub-basins at a monthly time resolution, and their derivation considers the methodological uncertainties related to global-scale EF studies. In addition to a lower bound of discharge based on existing EF methods, we introduce an upper bound of discharge in the EFE. This upper bound enables areas to be identified where streamflow has substantially increased above natural levels. Further, instead of only showing whether EFs are violated over a time period, we quantify, for the first time, the frequency, severity, and trends of EFE violations during the recent historical period. Discharge was derived from global hydrological model outputs from the ISIMIP 2b ensemble. We use pre-industrial (1801–1860) quasi-natural discharge together with a suite of hydrological EF methods to estimate the EFEs. We then compare the EFEs with recent historical (1976–2005) discharge to assess the violations of the EFE. These violations most commonly manifest as insufficient streamflow during the low-flow season, with fewer violations during the intermediate-flow season, and only a few violations during the high-flow season. The EFE violations are widespread and occur in half of the sub-basins of the world during more Published by Copernicus Publications on behalf of the European Geosciences Union. 3316 V. Virkki et al.: Globally widespread and increasing violations of environmental flow envelopes than 5 % of the months between 1976 and 2005, which is double compared with the pre-industrial period. The trends in EFE violations have mainly been increasing, which will likely continue in the future with the projected hydroclimatic changes and increases in anthropogenic water use. Indications of increased upper extreme streamflow through EFE upper bound violations are relatively scarce and dispersed. Although local fine-tuning is necessary for practical applications, and further research on the coupling between quantita tive discharge and riverine ecosystem responses at the global scale is required, the EFEs provide a quick and globally robust way of determining environmental flow allocations at the sub-basin scale to inform global research and policies on water resources management