Seasonal Precipitation Variability and Its Impact on Vegetation Dynamics under Climate Change and Aridity Spectra of the Southwest United States Ecosystems

This study combines hydro-climatological and biological components for addressing variability in precipitation and vegetation patterns under climate change. We explore the marginal and interactive effects of vegetation and atmospheric variables in order to better understand the plausible changes in terrestrial hydrological processes. We target the southwest United States, known for its diversified ecosystem and depleting water resources. Specifically, we employ an entropy-based disorder index to address precipitation variability and evaluate the marginal effect of watershed topography. Results show that the variability gradually increases westward. We concluded a significant watershed topography effect, which suggests that hilly reliefs have a stabilizing effect on seasonal precipitation variability in time and space. We conclude the necessity to include watershed topography information in climate model parameterizations. However, the implication of a spatial precipitation gradient raises questions regarding vegetation dynamics. In order to understand these dynamics, we analyze the inclusion of precipitation variability in conjunction with the Normalized Difference Vegetation Index (NDVI) during the growing season. We identify three climatic regions based on the United Nations Aridity Index (AI): a relatively humid region with AI≥0.65, an intermediate region with 0.50≤AI<0.65, and a relatively dry region with AI