Abstract
Global hydrological models (GHMs) supply key information for stakeholders and policymakers simulating past, present and future water cycles. Inaccuracy in GHM simulations, i.e. simulation ...results that poorly match observations, leads to uncertainty that hinders valuable decision support. Improved parameter estimation is one key to more accurate simulations of global models. Here, we introduce an efficient and transparent way to understand the parameter control of GHMs to advance parameter estimation using global sensitivity analysis (GSA). In our analysis, we use the GHM WaterGAP3 and find that the most influential parameters in 50% of 347 basins worldwide are model parameters that have traditionally not been included when calibrating this model. Parameter importance varies in space and between metrics. For example, a parameter that controls groundwater flow velocity is influential on signatures related to the flow duration curve but not on traditional statistical metrics. Parameters linked to evapotranspiration and high flows exhibit unexpected behaviour, i.e. a parameter defining potential evapotranspiration influences high flows more than other parameters we would have expected to be relevant. This unexpected behaviour suggests that the model structure could be improved. We also find that basin attributes explain the spatial variability of parameter importance better than Köppen–Geiger climate zones. Overall, our results demonstrate that GSA can effectively inform parameter estimation in GHMs and guide the improvement of the model structure. Thus, using GSA to advance parameter estimation supports more accurate simulations of the global water cycle and more robust information for stakeholders and policymakers.
Lake Baikal is the largest near-surface global freshwater source and of high interest for water quality alterations, as deterioration of water quality is a main global and an increasing issue in the ...Selenga River Basin. Here, the Selenga River Basin as main contributor to the inflow of Lake Baikal is extremely important. Pressure on ecosystems and water resources increased due to population growth, rapid urbanization and rising industrial activities, particularly in the mining sector. In this study, the large-scale water resources model WaterGAP3 is applied to calculate loadings of conservative substances (total dissolved solids) and non-conservative substances (faecal coliform bacteria and biological oxygen demand) in a spatially explicit way as well as in in-stream concentrations to get an insight into the state of water quality under current and future scenario conditions. The results show a strong increase in loadings in the scenario period and consequently increasing concentration levels. Comparing the sectoral contributions of the loadings, domestic and industrial sectors are by far the main contributors today and expected to be in the future. Furthermore, for all modelled substances and time periods, water quality thresholds are exceeded posing a potential risk to aquatic ecosystems and human health.
Major rivers worldwide have experienced dramatic changes in flow, reducing their natural ability to adjust to and absorb disturbances. Given expected changes in global climate and water needs, this ...may create serious problems, including loss of native biodiversity and risks to ecosystems and humans from increased flooding or water shortages. Here, we project river discharge under different climate and water withdrawal scenarios and combine this with data on the impact of dams on large river basins to create global maps illustrating potential changes in discharge and water stress for damâimpacted and freeâflowing basins. The projections indicate that every populated basin in the world will experience changes in river discharge and many will experience water stress. The magnitude of these impacts is used to identify basins likely and almost certain to require proactive or reactive management intervention. Our analysis indicates that the area in need of management action to mitigate the impacts of climate change is much greater for basins impacted by dams than for basins with freeâflowing rivers. Nearly one billion people live in areas likely to require action and approximately 365 million people live in basins almost certain to require action. Proactive management efforts will minimize risks to ecosystems and people and may be less costly than reactive efforts taken only once problems have arisen.
We present an improved water-scarcity metric we call water depletion, calculated as the fraction of renewable water consumptively used for human activities. We employ new data from the WaterGAP3 ...integrated global water resources model to illustrate water depletion for 15,091 watersheds worldwide, constituting 90% of total land area. Our analysis illustrates that moderate water depletion at an annual time scale is better characterized as high depletion at a monthly time scale and we are thus able to integrate seasonal and dry-year depletion into the water depletion metric, providing a more accurate depiction of water shortage that could affect irrigated agriculture, urban water supply, and freshwater ecosystems. Applying the metric, we find that the 2% of watersheds that are more than 75% depleted on an average annual basis are home to 15% of global irrigated area and 4% of large cities. An additional 30% of watersheds are depleted by more than 75% seasonally or in dry years. In total, 71% of world irrigated area and 47% of large cities are characterized as experiencing at least periodic water shortage.
Water quality monitoring is important for the management of freshwater resources in river basins. Allocation of monitoring stations is the first step in the design of a water quality network. For ...this task, planning objectives are identified and a Multi-Objective Artificial Bee Colony-based optimization algorithm is designed and implemented in a Geographic Information System framework. Specifically, the number of stations is minimized in a range of values at the same time that the detection of lower compliance areas, the affected population and the relative importance of the river stretches are maximized. The estimation of pollutant parameters such as Biochemical Oxygen Demand, Faecal Coliform Bacteria or Total Dissolved Solids is performed by using the WorldQual model. This allows to objectively allocate monitoring stations to rivers where no real measurements are available, and thus it is especially relevant to allocate water quality stations for the first time. This approach has been tested on the Great Fish River basin (South Africa), finding networks improving the values of the objective functions between 22.22% and 47.83% with respect to the ones of the current network. Moreover, the solution analysis provides insightful and valuable information to the decision maker.
•Approach to design water quality monitoring networks in river basins.•Identifying planning objectives with environmental, economic and social aspects.•Tested on Great Fish River with improved results (between 22.22% and 47.83%on the objectives).•It can be applied to river basins where no pollutant measurements are available.•It provides insightful and valuable information to the decision maker.
The supply of surface water by century-old infrastructure causes substantial water loss and triggers huge abstractions of groundwater, resulting in low irrigation efficiency. We evaluated the ...irrigation performance (application and conveyance efficiencies) and water availability (supply-demand) from the field to the Mungi Distributary canal level in Punjab, Pakistan. Between April–September 2019 and 2020, we monitored water delivery in the canal network, soil moisture content in cotton fields, and the canal and groundwater quality. The crops’ actual evapotranspiration was estimated using the AquaCrop model. We found conveyance efficiencies >90% for minor distributaries, 70–89% for watercourses, and ~75% for field ditches per kilometer. Field application efficiency was >90% for drip and ~35% for flood basin, whereas for raised-bed furrow, conventional furrow, and ridge-furrow irrigation methods, it varied between 44% and 83%. The deficits of canal water supply versus demand for cotton fields ranged from 45% to 73%, whereas the Mungi Distributary canal water showed a 68.6% and 19.8% shortfall in the April–September and October–March seasons of 2018/2019, respectively. The study suggests prioritizing improvements to field water application rather than canals with better water quality; additionally, surplus water from the Mungi canal in November and December could be stored for later use.
Humans directly change the dynamics of the water cycle through dams constructed for water storage, and through water withdrawals for industrial, agricultural, or domestic purposes. Climate change is ...expected to additionally affect water supply and demand. Here, analyses of climate change and direct human impacts on the terrestrial water cycle are presented and compared using a multimodel approach. Seven global hydrological models have been forced with multiple climate projections, and with and without taking into account impacts of human interventions such as dams and water withdrawals on the hydrological cycle. Model results are analyzed for different levels of global warming, allowing for analyses in line with temperature targets for climate change mitigation. The results indicate that direct human impacts on the water cycle in some regions, e.g., parts of Asia and in the western United States, are of the same order of magnitude, or even exceed impacts to be expected for moderate levels of global warming (+2 K). Despite some spread in model projections, irrigation water consumption is generally projected to increase with higher global mean temperatures. Irrigation water scarcity is particularly large in parts of southern and eastern Asia, and is expected to become even larger in the future.
Abstract
Renewable energy generation has great potential to reduce greenhouse gas emissions, however, it may exacerbate other environmental impacts, such as water scarcity, elsewhere in the supply ...chain. Here, we reveal a wide range of global environmental impacts of concentrated solar power, run-of-river hydropower, and biomass burning compared to classical coal-fired power: Spatially explicit life cycle impact assessment is used to evaluate their supply chains with respect to demand for energy, land, material, and water, greenhouse gas emissions, and impacts on human health and ecosystem quality with a focus on mining. Hotspot analyses in terms of location and type of impact show that there is no clear preference for any of the technologies, mainly because water consumption is often critical on-site. The examined concentrated solar power plant is the least suitable for a sustainable energy transition: Its spatial hotspots are spreading the furthest globally and may exceed those of coal combustion in number and severity. The presented methodology is the basis to mitigate such environmental hotspots.
This study assessed problems associated with irrigation water provisions and the potential barriers to the adaptation of the interventions (soil moisture sensors, on-farm water storage facilities and ...the drip method) under rotational canal water distribution in Punjab, Pakistan. Three groups of stakeholders were individually surveyed during September–December 2020: (i) 72 farmers, (ii) 15 officials, and (iii) 14 academicians. We used descriptive statistical analysis, cross-tabulation and the Fisher test to explore the pattern of responses across the groups. The main problems in the canal water distribution system were expressed by the farmers as limited water allocation, while academicians were concerned mostly with inflexibility and officials indicated discussion among neighbors. According to the farmers’ responses, the conventional depth/interval of irrigation is flooding the field with water and observing the plants, indicating over-irrigation behavior. Moreover, the most important barriers in the adaptation of the interventions that were highly rated by the three groups were low awareness, lack of training and financial resources. Additionally, farmers’ education revealed a statistically significant influence on awareness of soil moisture sensors and water storage facilities, while large farm holders showed a positive relationship to conducting a joint experiment with scientists and farmers’ associations on part of their land to improve water use efficiency.
WaterGAP is a global hydrological model that quantifies human use of groundwater and surface water as well as water flows and water storage and thus water resources on all land areas of the Earth. ...Since 1996, it has served to assess water resources and water stress both historically and in the future, in particular under climate change. It has improved our understanding of continental water storage variations, with a focus on overexploitation and depletion of water resources. In this paper, we describe the most recent model version WaterGAP 2.2d, including the water use models, the linking model that computes net abstractions from groundwater and surface water and the WaterGAP Global Hydrology Model (WGHM). Standard model output variables that are freely available at a data repository are explained. In addition, the most requested model outputs, total water storage anomalies, streamflow and water use, are evaluated against observation data. Finally, we show examples of assessments of the global freshwater system that can be achieved with WaterGAP 2.2d model output.
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