PNNL

Abstract

Reoccurring drought through the early 2000s has caused a serious water scarcity issue in the Colorado River Basin. Previous modeling studies focus more on the climate change impact but have not considered farmers' adaptive behaviors and the under-utilized Indian water rights. In this paper, we use a coupled Agent-Based (ABM)-water resource model to investigate how the farmers' adaptive decisions can affect water resources management under both climate change impacts and under-utilized Indian water right conditions. We used five General Circulation Model projections with RCP8.5 scenarios for the study. The results of farm-level decision making show different responses in irrigated areas to climate change impact. While winter precipitation change might partially explain the behavior tipping point, no specific pattern can be concluded based on their location. Also, farmers' responses on annual water diversion show more significant inter-year variation compared to irrigated areas. Basin level metrics show that climate change impacts will, in general, worsen water scarcity issues as measured in Navajo Reservoir storage, flow to Lake Powell and instream flow requirement. But these basin level's water scarcity metrics cannot reflect individual farm level's impact under climate change which is evidence of why modeling the bottom-up management actions is necessary. When the under-utilized Indian water rights are fully used, it is more likely to trigger the shortage sharing agreement due to the higher tribal water depletion. Evaluation of model uncertainty and a more realistic setup for adaptive actions under drought contingency plans are suggested for future research.