Understanding the Role of Climate and Socioeconomic Factors in Driving Irrigated Agriculture Dynamics in the Lower Colorado River Basin

Abstract

Understanding the dynamics of agriculture in relation to climate and socioeconomic variables such as market value is essential in assessing water use within a semi-arid basin. This study aims to improve understanding of the spatial and temporal variability of agriculture fallowing and crop productivity using satellite Normalized Difference Vegetation Index (NDVI), meteorological observations and socioeconomic data across two regions in Arizona: the Lower Colorado River Planning (LCRP) region in LCRP County and the Active Management Areas (PMAMA) in Maricopa County and Pinal County. A key difference between these regions is there access to water for irrigation: LCRP has 1st priority (senior) irrigation water access rights, whereas PMAMA has 3rd priority (junior) irrigation water access rights. Using Google Earth Engine, I produced annual extent of fallow and active croplands at high spatial resolution (30-m) from 2001-2017 by applying the Fallow-land Algorithm based on Neighborhood and Temporal Anomalies (FANTA) driven by 8-day normalized difference vegetation index (NDVI) for each region of interest. I then evaluated how factors including weather and market value have influenced management decisions for seasonal fallowing using statistical modeling. Results show that LCRP (with senior water rights) varied very little in agricultural extent from year to year (87 - 90% active) compared to PMAMA (77 - 84% active) potentially due to regional differences in growing season and water rights. Agricultural extent and productivity in both regions was found to be sensitive to biophysical factors, with LCRP most sensitive to aridity (R2=0.486) and PMAMA most sensitive to precipitation (R2=0.358). Finally, we found market value significantly increased regional climate sensitivity, such that agricultural productivity was highest when both biophysical constraints were low and market values were high. This research effort provides a framework and demonstrates the importance of separately analyzing patterns of agricultural extent and productivity, which I found to interact in complex ways with both biophysical (e.g., drought) and socioeconomic (e.g., market value) factors to explain year to year variability in total regional agricultural production.