How Does Irrigation Management Change Water and Energy Fluxes to the Atmosphere? A Case Study in Yakima River Basin

The economy of Yakima River Basin (YRB) is closely related to agricultural productivity. Nearly 60% of this basin is irrigated through gravitational or inefficient sprinkler systems. As a result of changes in cropping patterns and their new established irrigation systems and impacts of projected climate change, this current low efficiency is expected to be improved. Different irrigation systems alters water and energy fluxes through a change in the partitioning between evaporative, runoff and deep percolation (irrigation) losses, therefore with potential impacts on weather, water and energy balances, and crop functioning. To assess the impacts of change in irrigation management on irrigation losses, local weather and climate, and agricultural water availability two process-based models were dynamically coupled: a spatially-explicit macroscale hydrologic model, the Variable Infiltration Capacity (VIC) model, and a cropping system model, CropSyst. The VIC model simulates hydrological processes, while CropSyst simulates transpiration, crop growth and phenology. An irrigation module has been developed and added to the coupled framework. This module simulates irrigation losses and impact of irrigation evaporative losses on local temperature, humidity and crop transpiration. Results suggest a sensitivity of local weather and climate to different irrigation practices and significant changes in the YRB water and energy balance as a result of change in irrigation management.