Adaptive agricultural water resources management in a desert river basin: Insights from hydrologic modeling

Many arid and semi-arid areas around the world are projected to experience increasing aridity levels throughout the 21st century. The increase in the frequency and severity of droughts and changing precipitation patterns will likely intensify the water shortages. The widening gap between water availability and demand in arid and semi-arid areas necessitates better understanding of water quantity and quality issues in these regions. The objectives of this dissertation are: (1) reviewing the challenges of applying soil and water assessment tool (SWAT) watershed hydrology and water quality model in arid/semi-arid regions with irrigated agriculture; (2) robust analysis of water availability in an example desert river basin under plausible future climate conditions; and (3) evaluating water and land management interventions for adaptive water resources management and agricultural water sustainability. The results show the possibility of dryer future and more saline water resources, increasing the risks of crop loss, especially for high-value crops like pecan. The current agricultural water management practices that support growing pecan orchards will be difficult to implement in the future due to growing water shortages. It is timely for agricultural producers to develop preparedness to use water with marginal quality or take action to reduce the net consumptive water use of their operations by improving agricultural water management. Changing the crop pattern and applying deficit irrigation for water intensive crops like alfalfa helps reduce the irrigation water consumption while growing more drought resistant crops such as pistachio and pomegranate could improve the resilience of agricultural producers to long-term droughts. Challenges of modeling agricultural watersheds in arid/semi-arid regions are addressed in this dissertation to provide a technical road map for watershed modelers interested in applying SWAT