Self-governed irrigation systems cover about three quarters of global irrigated cropland. To feed more people without destroying additional habitat by land conversion or water diversion, irrigation efficiency needs to be improved on these lands. Maintaining and improving irrigation efficiency depends on functioning institutions at several levels, especially as the climate changes. Because user-organized collective action institutions are some of the few things irrigators can control beyond their land, the performance of these institutions is vital for adaptation to climate change. Three essential features of a commons - de facto access rights, user originated rules, and cultural norms - can greatly influence institutional and irrigation performance.

However, how these factors combine to influence performance under climate change is still not well understood. I use original data derived from a quasi-experimental research design, a rich social and environmental data time series (1984-present), and a stratified irrigation manager survey to investigate the San Luis Valley of Colorado. Here, culturally distinct groups of Hispanic and Anglo self-governing irrigation systems have been adapting snowmelt irrigation to a high desert valley for over 150 years and have recently faced signals of climate change.

Results indicate that access rights delimit institutional and irrigation performance, with systems possessing rights to water for longer durations having improved crop growth. Results also show that the performance of user-chosen adaptations, such as changing water distribution rules in times of shortage, can influence crop growth patterns. Finally, analysis reveals that cultural norms play a significant role in how rules are devised and implemented, leading to divergent irrigation outcomes. 

As the climate changes and global food security is challenged, these findings should highlight the importance of the influence of local institutions and adaptations on irrigation efficiency. Without understanding more about these systems' rules, policy and technology interventions may fail.

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