How do we rethink water planning in the face of a future shaped by climate change?

We live in a world full of uncertainties. The COVID-19 pandemic and the war in Ukraine are but two of the last examples. Climate change similarly comes with uncertainties, and we are seeing it with what happened in Texas in the last winter for instance: an unexpected change of “normal” climate conditions generated a serious humanitarian crisis due to the collapse of the power grid and water pipes, leaving millions without access to basic utilities.  

Extreme climate events like this one and others such as droughts, intense rains, and hurricanes will be more intense and frequent. Therefore, integrating uncertainty into our planning systems will be key to avoid catastrophes. In water planning, this is a very relevant issue: what actions should we take today to achieve water security in a deeply uncertain world? This is not a trivial question.

Take the example of the Mendoza River basin, Argentina. It’s a predominantly winegrowing and fruit-growing region, with important urban centers. It suffers from a 10-year long drought that adds to the consequence of the limited irrigation infrastructure that some agricultural areas have to deal with. This already complicated picture becomes even more uncertain when we consider other long-term challenges such as rising temperatures, decreasing rainfall, and melting glaciers, among others.  

How do you plan water supply in this case? The General Irrigation Department of the Mendoza province evaluated different infrastructure and management alternatives to anticipate these challenges, such as the construction of a large reservoir, a battery of small reservoirs, or a pressurized irrigation system. However, defining the best strategy depends on uncertain elements that are difficult to ponder: How and how much will climate change? How much will cities grow? Will the same crops remain in the basin? Which is the most cost-efficient strategy, and that at the same time ensures the supply for both drinking water and irrigation? 

Traditional planning systems are fragile in this context. Under deep uncertainty, looking for solutions by simulating only a few scenarios solutions is not enough. Fortunately, there are new techniques designed to analyze deeply uncertain problems and design solutions that satisfy objectives in multiple possible futures, such as Robust Decision Making (RDM). RDM also makes it possible to engage with several stakeholders in the decision-making process and include the evaluation of other development objectives. 

The IDB, together with DGI, and RAND corporation, prepared an RDM study that seeks to support DGI in the decision-making process of this water planning problem, which yields very interesting results for future applications in other countries of Latin America and the Caribbean. 

What did we do?  

• We met with the stakeholders of the basin and jointly defined the “problem framework”. Out of this exercise, we jointly determined that we would evaluate the performance, costs and benefits of the infrastructure under consideration of DGI: i) a large reservoir, ii), a battery of small reservoir, and iii) a pressurized irrigation system, under uncertainties such as climate change impacts and different scenarios of urban expansion and other land uses.  
• With this information, we modified a pre-existing WEAP model (a decision-support tool for integrated water resources management and policy analysis) to simulate the long-term performance of the system under uncertainty, with and without the infrastructure options above mentioned. We evaluated the current system performance under 840 plausible futures, each one reflecting a different assumption about climate trends, climate variability and changes in land use.  
• We found that Mendoza’s current water system is indeed vulnerable to changes in land use and climate change, especially in the agricultural sector. In addition, we carried out a vulnerability analysis in two sectors of the basin to understand the conditions under which the system could not satisfy the demand if it does not incorporate infrastructure or management changes. Doing so, we identified three general conditions that would lead to a high unsatisfied water demand.  
• Finally, we evaluated the system’s performance and vulnerabilities reduction if the prioritized infrastructure options were to be implemented. We found that increasing surface storage, whether through one or a few large reservoirs or a network of smaller reservoirs, would not mitigate these vulnerabilities significantly, and would be extremely costly. On the other hand, investments in a pressurized irrigation system would reduce vulnerabilities more significantly and cost-efficiently.  

The study provided DGI with new useful information for decision-making, in addition to providing a dialogue platform between stakeholders. While there are opportunities to improve the analysis, this proof of concept shows us that RDM provides a useful analytical framework to assess both the future water challenges, as well as different strategies that could be used to mitigate future water scarcity. As such, RDM proofs itself as a powerful support tool for other countries looking to strengthen their water planning processes and better afront the challenge of water security.