Modeling the impacts of regulatory frameworks on self-organization in dryland agricultural systems

Abstract:

The climatological conditions that characterize dryland environments – high potential evapotranspiration combined with low and variable total rainfall – pose challenges for farmers deciding when and how much to irrigate. These challenges are greater in developing countries where the absence of sufficient storage infrastructure means that irrigation water is sometimes applied to agricultural fields directly from rivers. Because soil moisture and river flow both depend on recent rainfall, high irrigation demand often coincides with low river flow, limiting access to water when it is most needed. These feedbacks can constrain the yield increases expected from irrigation in such settings.

Scaled up to the catchment level, irrigation water availability varies spatially as well as temporally. Irrigators in upstream areas of the catchment have first access to river water but rely on a smaller drainage network while those in downstream areas are affected by the opposite conditions. During periods of high rainfall, downstream users have the greatest access to water while upstream users are then favored during drought intervals. In the absence of rules governing water access, these flow dynamics will constrain the distribution of potential agricultural yields within the catchment.

A simple numerical model simulating catchment and irrigation processes was constructed in order to better understand how climate and geomorphologic characteristics affect crop yield, economic returns and the spatial distribution of irrigated areas. By assuming a statistically representative river network structure, the model was first used to explore the effect of unregulated irrigation withdrawals on these variables. Multiple water management programs, including withdrawal limits, rotational systems and flow minima, were then simulated and the results compared to the unregulated case. This analysis shows the potential for simple models to provide insight into complex irrigation systems and to make general predictions about the impact of different regulatory frameworks.