LONG-TERM PRECIPITATION TRENDS OF TWO UNIQUELY WATER-LIMITED ECOSYSTEMS: IMPLICATIONS FOR FUTURE SOIL MOISTURE DYNAMICS

Abstract

Roughly 40% of the Earth’s land surface is classified as arid or semiarid. These areas are expected to see changes in the frequency and magnitude of precipitation, which could have major implications for soil water resources, vegetation, water supply, and biome evolution. This study analyzed long-term precipitation trends in two water-limited ecosystems with bimodal precipitation regimes: a desert shrubland at the Santa Rita Experimental Range (SRER-SRC) and a mixed conifer system at the Santa Catalina Mountain Critical Zone Observatory (SCM-CZO). Specifically, we analyzed frequency and timing of precipitation in summer and non-summer seasons and compared seasonal precipitation patterns to soil moisture dynamics. Our study shows declining precipitation over the past few decades at both locations, with significant decreases in non-summer precipitation driving decreases in annual precipitation. We show that shallow soil moisture responds to storms of all sizes, and the deep layer responds to large storms or a series of small storms at both sites. Shallow soil moisture is especially vulnerable at SRER-SRC as a result of exponential water loss following a large storm. We expect that declining precipitation will have major implications for soil water resources and the healthy functioning of water-limited ecosystems. Note: This work is being further developed for future publication in the Water Resources Research journal in close collaboration with Shirley Papuga (University of Arizona) and Aloah Pope (University of Arizona).