Uncertainty Of Water Supply Research Articles

Constructing the Joint Probability Spatial Distribution of Different Levels of Drought Risk Based on Copula Functions: A Case Study in the Yellow River Basin

Joint multivariate distribution and calculation of return period are essential in enhancing drought risk assessment and promoting the sustainable development of water resources. Aiming to address the increasingly serious drought situation in the Yellow River Basin, this study first utilized the Soil and Water Assessment Tool (SWAT) distributed hydrological model combined with the Standardized Precipitation Evapotranspiration Index (SPEI), the Standardized Soil Moisture Index (SSMI), and the Standard Water Yield Index (SWYI); the duration, peak, and severity of meteorological, agricultural, and hydrological droughts were analyzed. Based on the selected copula function, a three-dimensional joint distribution of drought duration (D), drought severity (S), and maximum severity (M) was constructed. The corresponding copula joint probability was calculated, leading to the three-dimensional joint return period and concurrent return period of meteorological drought, agricultural drought, and hydrological drought. The findings reveal several key trends: (1) Meteorological drought intensifies over time. Although drought areas eased after the 1990s, the overall drought trend continues to rise. Agricultural drought has intensified in arid regions but eased in semi-humid areas after the 2000s. Hydrological drought was severe in the upstream regions during the 1990s but eased in the 2000s, while it was particularly severe in the midstream and downstream regions during the 2000s. (2) Meteorological droughts are more severe in arid and semi-arid temperate regions and milder in semi-humid cold temperate regions. Agricultural droughts are extreme in arid and semi-arid cold temperate regions. Hydrological drought events are fewer but more severe in semi-arid temperate regions and have the lowest probability of occurrence in semi-humid cold temperate regions. (3) The overall probability of the occurrence of meteorological drought is between 55.7% and 69%; that of agricultural drought is between 73.1% and 91.7%, and that of hydrological drought is between 66.9% and 84%. Drought risk assessment provides scientific references for the analysis of the uncertainty of water supply in the basin and the formulation of effective risk management strategies.

Conjunctive surface water and groundwater management in a multiple user environment

The conjunctive use of surface water and groundwater is practiced worldwide as a measure to address water supply uncertainty. This paper focuses on a scenario in which an aquifer is open to multiple users and examines the impact of such an open-access environment on the stabilization function of conjunctive management. We construct a non-cooperative stochastic dynamic game model where multiple users utilize groundwater intake from a common aquifer as a complement to fluctuating surface water. We also propose a simpler baseline applicable to dynamic environments to compute the benefits of the stabilization function when users are unable to adjust groundwater intake to surface water uncertainties. We then apply the model to the real-world case of the water supply environment of the Cao’e River in China. Simulation results show that open access leads to diminishing stabilization values as higher pumping costs due to declining stocks lead to a weakening of users’ incentive to utilize groundwater flexibly. Furthermore, the stabilization function itself is destabilized as the number of users increases. This is because greater groundwater intake and a decline in stocks amplify variations in pumping costs caused by different patterns of surface-water fluctuation.

Water resources allocation considering water supply and demand uncertainties using newsvendor model-based framework

A novel newsvendor model-based framework for regional industrial water resources allocation that considers uncertainties in water supply and demand was proposed in this study. This framework generates optimal water allocation schemes while minimizing total costs. The total cost of water allocation consists of the allocated water cost, the opportunity loss for not meeting water demand, and the loss of the penalty for exceeding water demand. The uncertainties in water demand and supply are expressed by cumulative distribution functions. The optimal water allocation for each water use sector is determined by the water price, the unit loss of the penalty and opportunity loss, and the cumulative distribution functions. The model was then applied to monthly water allocation for domestic, industrial, and agricultural water use in two counties of Huizhou City, China, whose water supply mainly depends on Baipenzhu Reservoir. The water demand for each water use sector and the monthly reservoir inflow showed good fits with the uniform and P-III distributions, respectively. The water demand satisfied ratio for each water use sector was stable and increased for the optimal water allocation scheme from the newsvendor model-based framework, and the costs were lower compared with the actual water allocation scheme. The novel framework is characterized by less severe water shortages, lower costs, and greater similarity to actual water use compared with the traditional deterministic multi-objective analysis model, and demonstrates strong robustness in the advantages of lower released surplus water and higher water demand satisfied ratio. This novel framework yields the optimal water allocation for each water use sector by integrating the properties of the market (i.e., determining the opportunity loss for not meeting water demand) with the government (i.e., determining the water price and the loss of the penalty for exceeding water demand) under the strictest water resources management systems.

Toleransi varietas jagung (Zea mays) terhadap cekaman kekeringan pada fase perkecambahan dan vegetatif menggunakan tingkat konsentrasi PEG 6000

Corn (Zea mays L) is the second strategic commodity after rice. Limitations and uncertainties in water supply due to global warming are factors causing drought stress on agricultural land. One strategy to develop maize on dry land is to develop drought-tolerant varieties. This study aimed to determine the effect of PEG 6000 with different concentrations of four maize varieties on the drought stress tolerance of maize during the germination and vegetative phases. This research was from August to November 2020 at BPTP Banten and the Soil and Agro-climate Laboratory, Department of Agroecotechnology, Faculty of Agriculture, Sultan Ageng Tirtayasa University. This study used a Completely Randomized Factorial Design (CRD) which consisted of two factors and three replications. The first factor is the corn variety which has four levels, namely A1 (Nasa-29), A2 (JH-27), A3 (JH 45), and A4 (Lamuru). The second factor is the concentration of PEG 6000 which consists of 5 levels, namely B1 (Control), B2 (5%), B3 (10%), B4 (15%), and B5 (20%). The results showed that each concentration of PEG 6000 produced varying results. Increasing concentrations of PEG 6000 decreased yields on vigor index, germination, root length, plumula length, seedling dry weight, and drought stress sensitivity index.

An optimization approach of water-food-energy nexus in agro-forestry-livestock system under uncertain water supply

Plantation, forestry, and livestock are inseparably intertwined and constitute the main sectors of the agricultural system. An integrated analysis of energy flow and material conversion processes of the agro-forestry-livestock system is beneficial for achieving sustainable and coordinated agricultural development. The availability of water resources is sensitive to climatic conditions and human activities, and uncoordinated water allocation affects the combined efficiency of various agricultural sectors. Therefore, an integrated modeling framework, based on the water-energy-food nexus under water supply uncertainty, is developed to maximize the performance of agro-forestry-livestock system. The advantages of the model include (1) systematic analysis of energy flow and material conversion processes in farmland, forest land and livestock; (2) consideration of trade-offs between economic benefits, multiple energy use efficiency (biomass, light energy), environmental impacts, and ecological benefits in the system; and (3) rational allocation of farmland, forest land, and livestock resources under the uncertainty of water supply. Empirical frequency analysis was used to obtain different frequencies of water supply. The model framework is based on a multi-objective programming model, which is solved by an affiliation function approach. The model constructs several objective functions, such as economic benefits, bioenergy productivity, light energy use efficiency, ecological economic benefits, and greenhouse gas emissions of the agro-forestry-livestock system. The concordance index was applied to evaluate the integrated performance of the model. The method was applied to Heilongjiang Province in northeastern China, where plantation, forestry, and livestock are predominant. Results show that livestock manure and urine have the highest energy potential, followed by wood, and straw has the lowest energy production. The main contribution to greenhouse gas emissions from the plantation is N2O, and the main contribution from livestock is CH4. The model had a higher concordance index for the larger water supply, but lower crop yield and photosynthetically active radiation. The proposed modeling framework contributes to the generation of stable and coordinated optimization solutions and provides decision makers methods and perspectives for sustainable agriculture.

Crop pattern optimization for the coordination between economy and environment considering hydrological uncertainty

With the rapid growth of population and economy, shortage and mismatch of land and water resources have deepened the need for cropping pattern optimization. In the context of the sustainable development of agriculture, cropping pattern optimization should not only pursue economic benefits, but the consequent environmental effects also deserve equal attention. Meanwhile, climate change increases the complexity of balancing conflicts of economic-environmental system by cropping pattern optimization. Therefore, this paper builds a multi-objective programming model for Economic-Environmental Synergistic Optimization for Cropping Pattern under Climate Change (EESO-CP-CC) model, with the goals of economic benefit increment and environmental pollutants emission reduction. The EESO-CP-CC model couples a non-point source pollution input-output model, a one-dimensional water quality model and an economic benefit function into an integrated framework. Fuzzy method was used to solve the optimization model, and the stochastic uncertainty of water supply under climate change was quantified by the integration of Bayesian approach and interval linear regression. The model was applied to Jinxi Irrigation District (JXID) in Heilongjiang Province, northeast of China. Results show that by adjusting the acreage of rice, corn and soybean, the harmony degree of economy-society-environment system increased by 10.7% compared to the current situation, indicating that the model tends to achieve the best possible economic benefits while ensuring the environmental effects. Compared with actual cropping pattern, the pollutants emissions reduced by 24.7% and 3% from corn and soybean, respectively. However, this led to a decrease of economic benefit by 8% in exchange, showing the trade-off between environmental pollution reduction and economic benefits improvement. The output coefficients of nitrogen and phosphorus pollutants were optimized, with the optimal output reducing by 20% compared to the standard. Cropping pattern and water resources allocation vary with different climate change conditions, however, the amplitude of variation is modest, indicating that the model can cope well with the changing environment. The developed model can help achieve synergistic development of economic benefits and environmental effects, and thus promote sustainable development of irrigation areas, and improve the coping capacity of agricultural water and land under climate change, by cropping pattern optimization and planning.

Multi-scale modeling for irrigation water and cropland resources allocation considering uncertainties in water supply and demand

Irrigated agriculture is the dominant user of world’s fresh water which feeds the world’s growing population. Conflicts between stakeholders; incompatibility of economic, social, and environmental development; and uncertainties in water supply and demand restrict the sustainable development of irrigated agriculture. This study developed a multi-scale multi-objective programming model for simultaneous optimal allocation of irrigation water and cropland to balance conflicts between farmers’ income and sustainable development of irrigation districts (reflected in economic, social, and environmental aspects). Consideration of the joint uncertainties of water supply and demand helps provide practical and indicative schemes for agricultural water and land allocation. The developed model was applied to a real case study in an irrigation district in northeast China. Farmers’ income, net economic benefit, resources allocation equity, and global warming potential were coordinated by optimally allocating limited water and cropland resources to different crops in different subareas under different combinational scenarios of water supply and demand. The performance of the model was evaluated, based on the concept of “adaptability” which can help realize the degree of ability of the irrigated agricultural system to adapt to changing environment. The developed model can help plan irrigation water and cropland resources in a sustainable way, and can be a reference for similar irrigation systems worldwide.

An evaluation model of water-saving reconstruction projects based on resource value flows

Due to uncertainties in water supply, there is growing demand for water resource management in enterprises. In this study, we evaluated the effects of companies’ water-saving reconstruction projects. We used Hina Advanced Materials Company as a case to construct an investment decision model to (1) calculate the internal and external costs of water resources based on circular economic value analysis theory, and (2) locate the level of water resources circulation. We adopted gray situation decision analysis to identify the typical problems that occur in water resource utilization. Moreover, we demonstrated optimization plans for different potential improvements, thereby providing guidance and references for water resource cost management and the comprehensive optimization of environmental benefits. We concluded that the circulation economic value analysis model can effectively display the flow and amount of value derived from water resource flows, thereby providing guidance and suggestions for optimizing water resource flows.

Optimal allocation of regional water resources based on multi-objective dynamic equilibrium strategy

Raising water demand, insufficient freshwater resources and uneven precipitation are the main causes of water conflicts in the river basin. The main challenges in water resources allocation are the following: first, the uncertainty of water supply caused by climate change; second, the dynamic allocation of water resources is not considered; third, there is a lack of equitable water allocation, which may lead to intensified conflicts among the water user sectors. Based on the above challenges, a multi-objective dynamic programming optimal water resources allocation model under uncertainties is established in this paper, which could be a resolution for water disputes as it addresses simultaneously economic, social and environmental benefits. The proposed model considers maximizing the minimum satisfaction degree of each water sector, maximizing the utilization efficiency of water resources in the basin, and maximizing economic benefits. Satisfaction degree function is introduced to optimize water allocation equality in water use sectors (agricultural, domestic, and industrial sectors), and economic efficiency loss acceptance is integrated into the model constraints to control the economic loss corresponding to variations in water availability. In addition, a case study demonstrated the practicality and rationality of the proposed model, and the model results proposed herein show significantly help for a single river basin. Most importantly, the results show that model with dynamic constraint ensures a greater overall economic return for the entire basin, and a larger variation in water resources of sub-area leads to a larger maximum economic efficiency loss. Moreover, the proposed model herein is flexible and can be used in other developing countries/regions only by modifying the parameters according to the actual situation.

The NSERC Canadian Lake Pulse Network: A national assessment of lake health providing science for water management in a changing climate

The distribution and quality of water resources vary dramatically across Canada, and human impacts such as land-use and climate changes are exacerbating uncertainties in water supply and security. At the national level, Canada has no enforceable standards for safe drinking water and no comprehensive water-monitoring program to provide detailed, timely reporting on the state of water resources. To provide Canada's first national assessment of lake health, the NSERC Canadian Lake Pulse Network was launched in 2016 as an academic-government research partnership. LakePulse uses traditional approaches for limnological monitoring as well as state-of-the-art methods in the fields of genomics, emerging contaminants, greenhouse gases, invasive pathogens, paleolimnology, spatial modelling, statistical analysis, and remote sensing. A coordinated sampling program of about 680 lakes together with historical archives and a geomatics analysis of over 80,000 lake watersheds are used to examine the extent to which lakes are being altered now and in the future, and how this impacts aquatic ecosystem services of societal importance. Herein we review the network context, objectives and methods.

Irrigation, risk aversion, and water right priority under water supply uncertainty.

This paper explores the impacts of a water right's allocative priority—as an indicator of farmers' risk‐bearing ability—on land irrigation under water supply uncertainty. We develop and use an economic model to simulate farmers' land irrigation decision and associated economic returns in eastern Idaho. Results indicate that the optimal acreage of land irrigated increases with water right priority when hydroclimate risk exhibits a negatively skewed or right‐truncated distribution. Simulation results suggest that prior appropriation enables senior water rights holders to allocate a higher proportion of their land to irrigation, 6 times as much as junior rights holders do, creating a gap in the annual expected net revenue reaching up to $141.4 acre−1 or $55,800 per farm between the two groups. The optimal irrigated acreage, expected net revenue, and shadow value of a water right's priority are subject to substantial changes under a changing climate in the future, where temporal variation in water supply risks significantly affects the profitability of agricultural land use under the priority‐based water sharing mechanism.

Water resources – an analysis of trends, weak signals and wild cards with implications for Russia

PurposeThis paper focuses on the long-term situation with water resources, and water sector in particular, analyzed through a Foresight study. The authors attribute particular attention to implication for Russia, which is relatively better positioned regarding the availability of water resources. However, the country still faces challenges related to the protection of water resources, drinking water supply, water networks, consumption patterns, water discharge, treatment and re-use. The present study aims at identification and analysis of trends, factors and uncertainties in water supply, demand, use and re-use with a particular focus on sustainability of water systems; water use by households and industry; and new water services and products.Design/methodology/approachResearch methodology in this paper involves a horizon scanning exercise for the identification of the key trends, factors and uncertainties along with the identification of weak signals of future emerging trends and wild cards in the form of future surprises, shocks and other unexpected events that may disrupt the preservation of water resources and the future of the water sector. Trends characterize broad parameters for shifts in attitudes, climate, policies and business focus over periods of several years that usually have global reach. These are usually experienced by everyone and often in similar contexts. Trends may represent threats, opportunities or a mixture of them, identified through underlying processes, possible events and other future developments.FindingsA key systemic restriction of water use for the next decades both globally and in Russia relates to competition between agriculture, energy, manufacturing and household water use. Given that the amount of renewable water resources is almost fixed and even decreases because of pollution, circular economy solutions for water use will be required. Implications of the global trends identified in the study for Russia are dependent on the overall situation with water resources in the country. Russia has sufficient water supply: the overall intake of water for drinking and economic purposes in Russia amounts to 3 per cent of the total water resources, two-thirds of which are discarded back to water bodies. At the same time, there are substantial problems associated with the extremely uneven distribution of water resources across the country, as well as high “water intensity” of the Russian GDP. The Russian water sector is currently not very attractive for investors. Moreover, it has significantly less lobbying opportunities than other infrastructure sectors, and this complicates its institutional and financial positions. Meanwhile, there have been some positive changes with regard to activities with a short pay-off period.Originality/valueThe paper offers one of the first studies on the future of Russian water resources with a focus on the water supply and sanitation sector. A comprehensive approach to trends identification (not found in other studies on Russian water resources) allowed authors to identify social, technological, environmental, economic, policy and value-related global trends and uncertainties. Moreover, implications of these trends and uncertainties, as well as Russia-specific trends, were outlined.

Uncertainty based assessment of dynamic freshwater scarcity in semi-arid watersheds of Alberta, Canada

Abstract Study region Alberta, Canada. Study focus The security of freshwater supplies is a growing concern worldwide. Understanding dynamics of water supply and demand is the key for sustainable planning and management of watersheds. Here we analyzed the uncertainties in water supply of Alberta by building an agro-hydrological model, which accounts for major hydrological features, geo-spatial heterogeneity, and conflicts over water-food-energy resources. We examined the cumulative effects of natural features (e.g., potholes, glaciers, climate, soil, vegetation), anthropogenic factors (e.g., dams, irrigation, industrial development), environmental flow requirements (EFR), and calibration schemes on water scarcity in the dynamics of blue and green water resources, and groundwater recharge. New hydrological insights for the region Natural hydrologic features of the region create a unique hydrological system, which must be accurately represented in the model for reliable estimates of water supply at high spatial and temporal resolution. Accounting for EFR, increases the number of months of water scarcity and the population exposed. Severe blue water scarcity in spring and summer months was found to be due to irrigated agriculture, while in winter months it was mostly due to the demands of petroleum or other industries. We found over exploitation of the groundwater in southern subbasins and concluded that more detailed analysis on groundwater flow and connectivity is required. Our study provides a general and unified approach for similar analyses in other jurisdictions around the world.

Integrating Supply Uncertainties from Stochastic Modeling into Integrated Water Resource Management: Case Study of the Saskatchewan River Basin

AbstractA warming climate and land management intensification have altered water supply characteristics in many regions of the world. Incorporation of water supply uncertainties into long-term water resources planning and management is, therefore, significant from both a scientific and societal perspective. This study proposes a set of analyses for integrated water resources management under changing water supply and demand expansion based on a newly developed methodology for vulnerability assessment. The basin of interest for the proposed analysis is the interprovincial Saskatchewan River Basin (SaskRB) in Canada, which supports a wide range of water demands, from municipal and industrial use to irrigated agriculture and hydropower. Proposals for an increase in irrigated area are used as a context for exploring the joint effects of current and future water supply uncertainty and increasing irrigation demand conditions on the water resources system. Changing water supply conditions are represented by pert...

Water Allocation Between the Agricultural and the Municipal Sectors Under Scarcity: A Financial Approach Analysis

A model examining the National Water Wealth (NWW) and its allocation between the municipal sector and the agricultural sector, where water value is defined as the present value of Water Rights, is presented. Five factors are considered: (i) uncertainty of water supply; (ii) population growth rate; (iii) the effect of time on NWW without new water production; (iv) agency costs, and; (v) production of new waters. The work is based on the model by Jensen and Meckling (J Finance Econ. 3:305–360, 1976), dealing with the effects of agency costs on the value of public companies. Agency costs are subject to conflicting interests between managers, shareholders and bondholders. In the water economy agency, costs stem from a divergence of interests between the government, the agricultural and the municipal sectors. Uncertainty of supply reduces water wealth of both sectors, with a stronger adverse impact on water wealth of the agricultural sector. Our model shows how production of new waters can have contributive effects on national water wealth. The modeling demonstrates the option of reducing the overall uncertainty of water supply and production of new waters which leads to favorable effects on the national water wealth.

Optimisation of water procurement decisions in an irrigation district: the role of option contracts

Water supply instability is one of the main risks faced by irrigation districts and farmers. Water procurement decision optimisation is essential in order to increase supply reliability and reduce costs. Water markets, such as spot purchases or water supply option contracts, can make this decision process more flexible. We analyse the potential interest in an option contract for an irrigation district that has access to several water sources. We apply a stochastic recursive mathematical programming model to simulate the water procurement decisions of an irrigation district's board operating in a context of water supply uncertainty in south‐eastern Spain. We analyse what role different option contracts could play in securing its water supply. Results suggest that the irrigation district would be willing to accept the proposed option contract in most cases subject to realistic values of the option contract financial terms. Of nine different water sources, desalination and the option contract are the main substitutes, where the use of either depends on the contract parameters. The contract premium and optioned volume are the variables that have a greater impact on the irrigation district's decisions.

Energy Implications of Water Transfer: Understanding Tradeoffs and Identifying Options

Water and energy are inextricably linked. Water is essential in almost all forms of energy production, while energy is required to extract, treat, distribute, and transfer water. The bulk of the literature discusses energy requirements to treat and extract water. But less attention has been paid to the energy requirements to distribute and transfer water. Indeed, such energy requirements represent a controversial topic, and one most often incorrectly assessed due to the lack of clear methodology and to the complexity of variables involved. Distributing and transferring water using high service pumps to end users can be extremely intensive in terms of energy and economy. For instance, distributing surface water in California, USA consumes 12 times more energy than treating the same amount of water (CEC, 2005; Bennett et al., 2010). In China, the energy requirements by pumps to transfer surface water is 99%, while 1% only goes for water treatment (Wang, 2008). Moving water often includes pumping the water over hills and mountains or into storage facilities, a process that can require large amounts of energy. As weather and rainfall patterns become more difficult to predict and the world’s population continues to grow, water transfer projects could play a significant role in increasing overall resilience to water supply uncertainty and achieving water security. Plans to meet future water demands in arid regions by desalinating sea water and building pipelines to transfer water from rich regions to scarce regions will also raise the energy requirements and cost of water supply. Governments have good reasons for moving water over long distances. Yet, a headlong rush into water transfer projects could bring its own challenges. Unless planned properly, water transfer projects are likely to increase competition for both water and energy, especially where it is already scarce. This paper seeks to provide policymakers with new insights for making tradeoffs between transferring water and other water supply options. The paper also seeks to establish a method for analyzing the energy intensity of water transfer, a method which could be essential in determining future strategies of water supply.

Optimizing Cropping Pattern Using Chance Constraint Linear Programming for Koga Irrigation Dam, Ethiopia

Optimal cropping pattern decisions without consideration to water supply uncertainty would result in yield/benefit that is less than expected and probability of system failure in meeting a given irrigation demand. In this study, a chance constraint linear programming (CCLP) model was used for optimizing cropping pattern for major crops grown at Koga Irrigation scheme, Ethiopia. The model incorporated uncertainty of inflow at exceedance probability of 90%, 80%, 70%, 60% and 50%. The model objectives were yield and benefit maximizations subject to land and water availability constraints. Each objective function has four scenarios. The models were solved using LINGO14. The cropping patterns under yield and benefit maximization models were found to be identical under all scenarios. However, the cropping patterns of each model varied among scenarios. The study showed that the possibility of irrigating 5904.3 to 8051.0 hectares of land at 80% by optimizing cropping patterns at irrigation efficiency of 48%. This could increase the yield by 108 to 153%, benefit by 153 to 208% and physical water productivity by 132% to 186% and economic water productivity by 205% to 241% of the actual values. In conclusion, the irrigated land in 2012/13 was below the optimal value and the irrigation water was mismanaged. Therefore, with optimal crop planning and water management, the design command area of 7000 ha could be irrigated. Finally, a study should be made to determine optimal levels of crop water deficit that maximize water productivity.

IMPACTS OF WATER SUPPLY UNCERTAINTY AND STORAGE ON EFFICIENT IRRIGATION TECHNOLOGY ADOPTION

AbstractIn the framework of a stochastic dynamic programming model, the paper investigates the impact of water supply uncertainty and storage at farm level on adoption of efficient irrigation technologies under a flexible water price regime. We find that even a flexible water pricing cannot guarantee higher adoption of efficient irrigation technology in all cases. Results of the paper indicate that if a farmer invests in water storage capacity, then the value of efficient usage of water increases, and the rate of adoption of efficient irrigation technology will be higher. It establishes a complementarity relationship between investments in storage capacity and adoption of efficient irrigation technology. The relationship becomes stronger with increasing variance in water supply. In a situation without any option to store water at the farm level, we find a negative relationship between investment in efficient irrigation technology and water variability. However, numerical analysis results suggest that a risk averse farmer may invest more in efficient irrigation only if the variance in water supply is very high.

Think globally: Replace disaster response with risk management

Increasing demand for water, uncertainties in water supply, and escalating risk to infrastructure create urgency around the need for water supply portfolios to be re‐evaluated.