An Examination of Extreme Rainfall and Non-Stationary Climate Patterns in Southeastern Arizona

Abstract

Given the recent decades of research and debate about anthropogenic climate change, deeper understanding is needed to clarify how our world is changing as result of increasing atmospheric CO2 concentrations. As of 2025, Earth continues to play host to an increasing array of natural disasters that put vulnerable communities at risk. During this time, Arizona has seen significant residential and industrial developments despite stressed water supplies from key sources such as the Colorado River. Since the mid-1990s, the southwestern US has been experiencing a period of prolonged aridity known as the Mega-Drought. In this time, summertime monsoon-driven thunderstorms have increased in maximum intensity, bringing greater risks for flash flooding and erosion while stressing catchment water balances. This study examines the distribution and stationarity of extreme rainfall events observed at the Walnut Gulch Experimental Watershed located in Tombstone, Arizona. Our analysis relies on a data set compiled from 85 rain gauges, measuring at 5-minute intervals, with 61 years of historical record. We examined the annual maximum rainfall across the 147 square kilometer watershed and estimated IDF curves from the GEV probability distribution. We observed areas of consistent high and low extreme storm probabilities within the watershed boundary, contrary to typical assumptions of homogeneity in this region, and produced extreme, short-duration rainfall estimates which exceeded NOAA’s values. To examine the stationarity over time, annual rainfall trends were calculated in a variety of contexts with storm return-levels derived from the MEV probability distribution. Our results show an overall positive trend in extreme storm intensities and a negative trend in annual rainfall totals.