3.1. Enhancing environmental flows with improved institutional cooperation
Adjusting the current Institutional cooperation (IC) in the Ebro basin augmented by Environmental institutional cooperation (EIC) is prescribed by more fully accounting for the benefits of environmental flows in river reaches. In this light, EIC achieves better ecosystem protection than the existing IC, delivering more environmental flows even with reduced cultivated land (-13%) and energy generation (-5%) (Fig. 2a). The EIC policy generates a significant increase of environmental flows in all rivers reaches, enlarging the streamflow at the Ebro mouth by about 180 Mm3 per year. That EIC policy reveals a significant improvement of ecosystem status across the full range of watersheds in the basin (Fig. 2c).
Water use in agriculture under EIC compared to IC is reduced by 14%, although impacts on agricultural economic benefits are modest (-2%) because farmers reduce cultivation of field crops, which have high water requirements and minimal income generating capacity. Economic benefit gains remarkably complement gains in environmental benefits of €170 million, for which some economic benefits are lost at a level of about €20 million both energy and agriculture (Fig. 2b). These results reveal trade-offs between the environment and the economic sectors, if decision makers implement protection of environmental flows.
Reduced withdrawals by the largest water consuming sector (agriculture) increase stream flows in rivers across the basin. The increase is an important buffer during droughts for protecting ecosystems and economic activities. Therefore, relative to unadjusted IC, EIC enhances both economic water security and aquatic biodiversity during periods of water scarcity and represents a risk management policy to advance.
3.2. Sectoral responses and competition: Tradeoffs analysis under future climate scenarios
Understanding the complex relationship among water, energy, food and ecosystems provides essential insights for development of future sustainable water planning. Tradeoffs among competing water uses in the Ebro basin by policy and climate scenario (CC-2070 and CC-2100), for which results are presented in Fig. 3.
Information from the tradeoff analysis guides the design of water management strategies. These strategies have the capacity to address challenges of future elevated water vulnerability by identifying workable and science-informed benefit-sharing schemes. Climate change reduces considerably baseline inflows, by 1500 and 3000 Mm3 for CC-2070 and CC-2100 scenarios, respectively. The agriculture and urban water consuming sectors would curtail water withdrawals with only modest economic losses, depending on the policy option. An unadjusted IC policy (status quo) is the weakest-performing strategy for adapting to climate change, for which there is a poor economic benefit outcome, largely explained by lower ecosystem benefits, driven by smaller environmental flows as a result of high irrigation withdrawals (Table 2).
Table 2
Land use, energy production, water use, and benefits by climate change scenario and management policy. Figures for climate change scenarios are yearly averages of 30 simulation runs over the 30 years periods 2040–2070 and 2070–2100.
Climate scenarios | Baseline | CC-2070 | CC-2100 |
Policies | IC | IC | EIC | IM | EDS | WM | IC | EIC | IM | EDS | WM | |
Land (1000 ha) | 541 | 503 | 425 | 431 | 424 | 416 | 441 | 371 | 377 | 371 | 353 | |
Field crops | 384 | 351 | 277 | 282 | 276 | 268 | 299 | 229 | 233 | 228 | 211 | |
Fruits trees | 121 | 116 | 115 | 115 | 115 | 115 | 109 | 111 | 112 | 111 | 111 | |
Vegetables | 36 | 35 | 33 | 34 | 33 | 33 | 33 | 31 | 32 | 32 | 31 | |
Flood | 293 | 265 | 214 | 17 | 213 | 208 | 225 | 180 | 14 | 180 | 168 | |
Sprinkler | 158 | 151 | 125 | 268 | 125 | 122 | 133 | 107 | 222 | 107 | 101 | |
Drip | 90 | 87 | 86 | 146 | 86 | 86 | 83 | 84 | 141 | 84 | 84 | |
Hydropower (GWh) | 8710 | 8288 | 8060 | 8064 | 9975 | 8068 | 7553 | 7361 | 7373 | 9263 | 7384 | |
Reservoir | 6401 | 5987 | 5835 | 5837 | 7130 | 5840 | 5425 | 5286 | 5296 | 6574 | 5298 | |
Run-of-river | 2309 | 2301 | 2225 | 2227 | 2845 | 2228 | 2128 | 2075 | 2077 | 2689 | 2086 | |
Water use (Mm3) | | | | | | | | | | | | |
Agriculture1 | 4248 | 3948 | 3282 | 2953 | 3285 | 3206 | 3459 | 2831 | 2539 | 2830 | 2665 | |
Urban | 454 | 401 | 401 | 401 | 401 | 454 | 346 | 346 | 346 | 346 | 452 | |
Energy | 32082 | 30935 | 32437 | 32487 | 31930 | 32465 | 28905 | 29980 | 30017 | 29610 | 30028 | |
Streamflow at Ebro mouth (Mm3) | 9287 | 7827 | 8014 | 8124 | 8156 | 8028 | 6983 | 7183 | 7312 | 7406 | 7238 | |
Social benefits (M€) | 4951 | 4772 | 4896 | 4923 | 5002 | 4931 | 4494 | 4596 | 4615 | 4697 | 4741 | |
Agriculture | 1008 | 1006 | 980 | 1027 | 981 | 980 | 981 | 956 | 1005 | 957 | 963 | |
Urban | 2655 | 2617 | 2617 | 2617 | 2617 | 2654 | 2502 | 2502 | 2502 | 2502 | 2647 | |
Energy | 400 | 382 | 368 | 369 | 463 | 368 | 349 | 337 | 338 | 429 | 338 | |
Ecosystems | 888 | 767 | 944 | 951 | 955 | 948 | 662 | 826 | 834 | 835 | 834 | |
Expenses by CHE2 | | | -13 | -41 | -14 | -19 | | -25 | -65 | -26 | -42 | |
IC: Institutional cooperation, EIC: Environmental institutional cooperation, IM: Irrigation modernization, EDS: Enlarging dam storage capacity, WM: Water markets. |
1: Water use for agriculture is the sum of net withdrawals entering irrigation districts, without including losses of upstream main canals. |
2: Expenses by CHE are the public funds used by the basin authority to buy water for the river. |
Under the EIC, IM, EDS, and WM policy options, the water authority would assign water for the environment to improve ecosystem status.[1] These policies deliver higher economic benefits than an unadjusted IC, reducing risks of water stress and improving environmental sustainability under climate change. The EIC, IM, and WM policies deliver more environmental flows, while reducing irrigated land and energy production, compared to IC (Table 2, Fig. 3a). The EDS policy increases energy production and environmental flows over any other policy, while reducing cultivated acreage compared to IC (Fig. 3). These results show the tradeoffs between environmental and economic activities under future climate scenarios. They also highlight the difficulties of achieving win-win outcomes that jointly ensure water, energy and food security, together with ecosystem protection, a common challenge faced by scientists, stakeholders, and water managers in large and complex basins.
Differentiating IC and EIC with climate change conditions is similar to that without climate change. Compared to the IC policy, the EIC policy reallocates water among economic activities and the environment to maximize total economic welfare, while respecting relevant constraints, by reducing irrigation withdrawals and increasing environmental flows, augmenting streamflow at the Ebro system mouth by 300 and 200 Mm3 for CC-2070 and CC-2100 scenarios, respectively. In both climate scenarios, an EIC program increases environmental benefits by about €170 million and overall economic benefits by about €100 million, compared to the base IC policy (Table 2). The water authority would also acquire 670 Mm3 of water for the river at a cost of €13 million in CC-2070, and 630 Mm3 at a cost of €25 million in CC-2100 (online supplementary material section 6 [SM6]). The EIC policy requires implementing resource and benefit sharing that would advance ecosystem biodiversity, water security, and resilience and improve adaptation to climate change.
Achievement of the food security goal is elevated under the unadjusted IC and IM policies. However, IM has clear advantages over IC because modernization investments involve upgrading irrigation technologies, which improve water use efficiency in irrigation, boost ecosystem status, and increase private and social benefits. Compared to IC, modernizing irrigation systems could reduce agricultural water withdrawals by around 1000 Mm3 and increase streamflow at Ebro mouth by 300 Mm3, with large gains in social benefits between 120 and €150 million for future climate scenarios. The water authority purchases around 1000 Mm3 under the IM policy, spending €41 million in CC-2070 and €65 million in CC-2100 (online supplementary material section 6 [SM6]), and increasing environmental benefits by around €170 million. The IM policy remains instrumental for achieving water and food security goals and enhancing aquatic biodiversity in the Ebro basin.
EDS is an essential policy for adapting to periods of water scarcity during droughts. As a risk management strategy, it buffers against fluctuations in water supply by permitting augmented water storage with greater reservoir storage capacity, with optimized reservoir releases covering economic and environmental demands in a controlled manner which dampen the economic costs of droughts when they occur. The EDS policy achieves improved results for economic benefits as well as producing top performing result for energy security, in both CC-2070 and CC-2100 scenarios. For both scenarios, EDS supplies about 1700–1800 GWh of additional energy generation and about €100 million of additional energy benefits based on the power prices we used. This policy also achieves better performing ecosystem protection, most noticeable in mountain and delta watersheds, by delivering more water for the environment. The water authority purchases about 650 Mm3 of water for the river, spending €14 million in CC-2070 and €26 million in CC-2100. Compared to other policies, EDS increases streamflow at the Ebro system mouth between 30 and 330 Mm3 in CC-2070, and between 100 and 420 Mm3 in CC-2100. EDS performs well for supplying clean energy, protecting ecosystems, and augmenting both water and energy security. It is also a high-performing measure to build resilience and adaptation to climate change.
The WM policy reallocates the available water among sectors from lower to higher economic valued uses. Water trading takes place not only between economic activities but also with the environment, through water purchases for the river by the basin authority. Market trading results in economic welfare gains by moving water among sectors, locations, and time periods, mitigating economic impacts of future climate water stress. The WM policy enhances the economic performance of urban use, the highest economically valued sector for water use, but generates moderate outcomes for agriculture and energy. Water exchanges among irrigation districts are only 8 and 25 Mm3 in CC-2070 and CC-2100, respectively. Water trading from irrigation districts to urban centers is around 50 Mm3 in CC-2070 and 100 Mm3 in CC-2100. Purchases of water for the river by the basin authority from irrigation districts amount to about 690 Mm3, with costs at €20 million in CC-2070 and €40 million in CC-2100 (online supplementary material section 6 [SM6]). These efficient water reallocations between competing sectors achieve the highest economic returns in CC-2100 (€4741 million), and the second-highest economic returns in CC-2070 (€4931 million) only behind EDS. This policy achieves the top performing urban economic benefit, which improves the performance of human water security, while also providing ecosystems protection.
Policy choices for best adapting to future climate water stress depend on society’s goals. If the priority is food production, then both unadjusted IC and IM deliver higher agricultural benefits, although IM secures higher stream flows across the basin and enhances environmental benefits. The policy choice for energy priority is EDS, which delivers higher energy production with gains in energy benefits close to 30% over other policies. The choice for urban supply priority is WM which augments urban water use (+ 30%) and benefits (+ 6%) over other policies, but also reduces food production. If ecosystems are a priority, then all policies deliver high environmental benefits except the current unadjusted IC.
3.3. Climate risk management: resilience and adaptation
There remains considerable interest by policymakers in discovering measures to improve the climate resilience of water sectors, and to more effectively deal with shrinking water supplies in arid and semi-arid regions. A number of strategies can be undertaken for reducing risks of water stress and its subsequent economic losses. Results in the Ebro under climate change indicate that compared to IC (business as usual), all other management strategies (EIC, IM, EDS, WM) reduce agricultural water withdrawals and increase stream flows across all watersheds in the basin (Fig. 4). Improving the resilience of water resources to adapt to climate change involves more efficient use of water and larger environmental flows, while finding a workable balance between food, energy and human water security.
The economic analysis of strategies assesses costs and benefits of policies which are tracked by sector, stakeholder group, spatial location, and time period. The optimization model developed for this paper is a powerful framework for informing policy debates and guiding adaptation to the ongoing evidence of climate change. The success or failure of policy interventions will depend on the equitable sharing of costs and benefits among stakeholders (Segerson 2022), including compensations where needed for losers. Findings indicate that all alternatives assessed to the current policy (IC) increase net economic welfare (Table 2), despite the high investment and operating costs associated with some water management strategies, such as investments required for irrigation modernization (IM) or to augment dam storage capacity (EDS). These gains in social benefits could contribute to financing compensations to groups of stakeholders facing losses from policy changes. When the gains exceed the losses, the result is the well-known Potential Pareto Improvement (Baah-Kumi and Ward 2020; Goulder and Williams 2012; Habteyes et al. 2015; Zheng et al. 2021).
[1] In all policy and climate scenarios, most water trading comes from Bardenas, RAA, Urgel and A&C irrigation districts (online supplementary material section 1 [SM1], Fig. S1). These districts have low shadow prices of water (0.02–0.06 €/m3) and large water sales (between 100 and 200 Mm3) (online supplementary material section 6 [SM6], Tables S1-S3).