Five Decades of Observed Daily Precipitation Reveal Longer and More Variable Drought Events Across Much of the Western United States

TLDR

Climate change is expected to increase precipitation variability, leading to more frequent extreme events that could have significant socio‑ecological impacts in water‑limited regions of the western United States. This study analyzes daily meteorological observations from 1976 to 2019 at 337 long‑term weather stations across the western United States. The analysis quantifies trends in temperature, precipitation, and dry‑interval statistics to assess changes in drought frequency and duration. Results show a warming trend of 0.2 °C per decade, a decline in annual precipitation of 2.3 mm per decade, and increasing interannual variability, with extreme‑duration droughts becoming more common and longer dry intervals rising by 0.6 days per decade, indicating intensified precipitation variability that threatens ecosystem services.

Abstract

Abstract Multiple lines of evidence suggest climate change will result in increased precipitation variability and consequently more frequent extreme events. These hydroclimatic changes will likely have significant socioecological impacts, especially across water‐limited regions. Here we present an analysis of daily meteorological observations from 1976 to 2019 at 337 long‐term weather stations distributed across the western United States (US). In addition to widespread warming (0.2 °C ± 0.01°C/decade, daily maximum temperature), we observed trends of reduced annual precipitation (−2.3 ± 1.5 mm/decade) across most of the region, with increasing interannual variability of precipitation. Critically, daily observations showed that extreme‐duration drought became more common, with increases in both the mean and longest dry interval between precipitation events (0.6 ± 0.2, 2.4 ± 0.3 days/decade) and greater interannual variability in these dry intervals. These findings indicate that, against a backdrop of warming and drying, large regions of the western US are experiencing intensification of precipitation variability, with likely detrimental consequences for essential ecosystem services.