Stacy K. Tanaka

Economic consequences of optimized water management for a prolonged, severe drought in California

If abrupt climate change has occurred in the past and may be more likely under human forcing, it is relevant to look at the adaptability of current infrastructure systems to severe conditions of the recent past. Geologic evidence suggests two extreme droughts in California during the last few thousand years, each 120-200 years long, with mean annual streamflows 40%-60% of the historical mean. This study synthesized a 72 year drought with half of mean historical inflows using random sampling of historical dry years. One synthetic hydrological record is used, and sensitivity to different interpretations of the paleorecord is not evaluated. Economic effects and potential adaptation of Californias water supply system in 2020 to this drought is explored using a hydroeconomic optimization model. The model considers how California could respond to such an extreme drought using water trading and provides best-case estimates of economic costs and effects on water operations and demands. Results illustrate the ability of extensive, intertied, and flexible water systems with heterogeneous water demands to respond to severe stress. The study follows a different approach to climate change impact studies, focusing on past climate changes from the paleorecord rather than downscaled general circulation model results to provide plausible hydrologic scenarios. Adaptations suggested for the sustained drought are similar for dry forms of climate warming in California and are expensive but not catastrophic for the overall economy but would impose severe burdens on the agricultural sector and environmental water uses.

Climate Warming & California's Water Future

Few states depend more on climatic stability than California. While the California water system is designed fairly well to accommodate repeats of historical droughts in the near future, there is concern that California might not be able to easily accommodate major droughts in the more distant future, especially with the hydrologic consequences of significant climate warming. This study developed comprehensive surface and ground water hydrologies for 12 climate warming scenarios for Californias inter-tied water system, as well as economic water demand estimates for urban and agricultural uses for estimates 2100 population levels. The most severe of these 12 climatic warming hydrologies was then employed with these 2100 economic water demands as inputs into an integrated economic-engineering optimization model of Californias inter-tied water system (CALVIN). The results indicate the effects of population growth and climatic change on the performance of Californias water system, as well as promising water management strategies to respond to these changes in supply and demand conditions over the coming century.

Water Resources Impacts

Models are used to estimate potential physical and biological impacts, efficient adaptations, and residual damages from climate change. The contributors cover a broad array of climate change impacts on affected market sectors (including water supply, agriculture, coastal resources, timber, and energy demand) as well as ecosystems and biodiversity. An integrated hydrologic-agriculture model is developed to explore how the region would adapt to changes in water flows. Interactions between climate impacts and population and economic growth, urbanization, and technological change are also explored. For example, the study examines how both climate change and projected land development affect the region’s terrestrial ecosystems and biodiversity.

Extreme Drought and Water Supply Management in California

The geological record contains extreme droughts beyond those seen in historical hydrologic records. For California, the geological record contains several extreme droughts the last few thousand years. Two of these droughts are 120-200 years long, with mean annual streamflows between 40% and 60% of the historical mean. This study synthesized a 72-year historical record for a drought of this character, having a mean flow of 40% of the historical record. This hydrologic time series was used as input to an economic-engineering optimization model of California’s water supply system (CALVIN). The model allows exploration of how California’s water management system might respond to such an extreme drought and provides preliminary estimates of economic costs and effects of such a drought on water operations and demands. The overall results show the importance of management flexibility and adaptation in response to extreme stresses on water systems. Results also illustrate the physical ability of extensive, diversified, and highly intertied water systems with heterogeneous water demands to economically respond to such extreme stresses. The study provides a different approach to climate change studies, focusing on observed past changes in climate from the geologic record rather than downscaled general circulation model results to provide hydrologic scenarios.

Computer support for implementation of a systemic approach to water conflict resolution by V. Rajasekaram, S. Simonovic, and K. Nandalal

We see an increasing need for support to resolve multiparty water resources conflicts, and Rajasekaram, Simonovic, and Nandalal introduce the systemic approach as a “powerful tool for deep inquiry and development of stakeholder dialogue” (p. 457). Their prototype Conflict Resolution Support System (CRSS) links multi-criteria decision making (MCDM), using compromise programming, with modules for image and map viewing, statistical analysis, river flow estimates, and reservoir routing. System development is motivated by a need to promote internal efforts to resolve conflicts while minimizing use of external assistance and dependence on external intervention. We find the system approach valuable. It offers openness, dialogue, and reflexive thought as constructive roles parties should adopt to deal with conflict. However, we question whether generic software architectures, such as CRSS, can implement the systemic approach in a standalone fashion. For example, what will motivate parties to engage the computer and accept the analysis algorithms chosen by the model developers? How do natural language programming and artificial intelligence improve stakeholder dialogue and independence when they cast the computer as a mediator limited by the schema and algorithms programmed into it? And, can compromise programming generate new proposals for parties to evaluate? We raise these concerns to emphasize that willing participants and capable mediators – in addition to computer support – seem essential to systemically approach and resolve water conflicts.