Flexible water allocations and rotational delivery combined adapt irrigation systems to drought

摘要

Self-governing irrigation systems are integral to global food security and face serious problems under climate change. This is particularly true in areas expected to become more arid such as the Southwestern United States, where restrictive water rights are strictly enforced. Adaptations to these dual climatic and legal challenges include user-selected rules. In particular, during water shortage self-governing irrigation systems often change water allocations between members and rotate water delivery. However, it is unclear how these rules interact with each other as configurations and with contextual factors, such as the degree of water scarcity. It is also unclear how these rules influence outcomes between irrigators closer to the water source and those farther from it. How might different configurations of rules interact with water availability to produce outcomes along an irrigation systems canal network? This study addresses this question by exploiting a natural experiment in water distribution and allocation rules during shortage among a stratified sample of 60 snowmelt dependent irrigation systems in the San Luis Valley of Colorado during a four-year drought period from 2011-2014. A key finding is that the combination of rotational delivery and flexible water allocations produces the most equal crop growth between irrigators at the head and tail of the irrigation system at all levels of water availability. The marginal productivity of water at the head and tail end of irrigation systems at all levels of water availability is also equalized under this configuration. These results suggest a greater likelihood of ongoing collective action, important for climate change adaptation. However, rotation with flexible allocations is outperformed by other configurations depending on context. These findings highlight the configurational relationships between rules, further illustrate interactions between rules and physical context, and caution against panaceas in water resource management and climate change adaptation.