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Quantifying evapotranspiration (ET) is a key element for achieving better water management, especially in regions where agriculture is the main water consumer. A hybrid model combining the SEBAL and RESET models (s-RESET) was developed to effectively estimate actual ET (water use) of the agriculture sector around the Phoenix metropolitan area. To examine how irrigated agriculture water consumption varies with climate, the S-RESET model was applied under wet and dry climatic conditions. Results show that the average ET for active agriculture is 9.3 mm/day (+/- 3.8mm/day) during the study period. Seasonal water use was 438 mm for 2000 (drought) and 494 mm for 2008 (wet). Based on the seasonal ET, we concluded that farmers in arid region use the same amount of water regardless of climatic conditions, implying that the agriculture sector as a whole may not be sensitive to drought as long as there is sufficient water from irrigation. This finding carries significant implications for the region’s water security.