Longer intervals between rainfall and increasing interannual variability compound soil moisture drought across the western United States

Abstract:

Hydroclimatic change includes well-documented trends in annual temperature and precipitation totals. However, ecosystems may be more significantly impacted by interannual variability and extreme events, such as the duration of extreme drought between rainfall events. While there is growing attention given to such climate extremes, the gridded datasets and/or temporal aggregation used in many studies may subdue extremity. To address this knowledge gap, here we present an analysis of daily meteorological observations from 1976 – 2015 at 463 long-term weather stations distributed across the western United States (US). We examine trends in the mean and variability of precipitation and ecologically critical attributes of precipitation timing including the dry intervals between precipitation events. In ongoing research, we apply a soil water model to quantify how these changes in precipitation amount and timing have altered the frequency and severity of drought for the dominant vegetation types in each of the eight NEON domains of the Western US.

We found most parts of the western US became significantly drier, with increased maximum temperatures, lower rainfall totals, decreased numbers of precipitation events, and greater interannual variability in most rainfall characteristics. Critically, daily observations showed that extreme-duration drought is becoming more common, with increases in both the mean and longest dry interval between rainfall events and greater interannual variability in these characteristics. These findings indicate that large regions of the western US are experiencing intensification of multiple factors that contribute to socioecological drought, with likely detrimental consequences for essential ecosystem services needed to support this region.