Beyond Expectations: Investigating Anomalous 2022–23 Winter Weather Conditions and Water Resources Impacts in California

Abstract The 2022–23 winter in the western United States, particularly in Southern California, experienced unusually wet and cold conditions, prompting vigilant water management. This study chronicles the water year, highlighting the challenges state water managers faced as California shifted from extreme drought to elevated flood risks due to an unprecedented “weather whiplash” and a subsequent record-setting snowpack. By analyzing precipitation and temperature data from 2002 to 2023, the research highlights the anomalous nature of these variables in California during this period. It focuses on the impacts of atmospheric rivers (ARs) due to their proven influence on seasonal precipitation patterns and intensities, examining their hydrologic impacts—specifically, snow water equivalent (SWE) in Sierra Nevada and reservoir storage—compared to other high precipitation years in California to gauge the effects of this atypical weather on water resources. The study reveals that Southern California’s wintertime precipitation in 2022–23 was the highest in over two decades. Precipitation was closely linked to the occurrence of 11 moderate to strong ARs, which alleviated the state’s drought conditions—94% of California was drought free by the end of the water year. Additionally, the mean maximum temperature was below the long-term average during spring and summer, decelerating snowpack melt and mitigating flood potential. Notably, 2022–23 saw the most significant increases in SWE and reservoir storage among the years analyzed. This research delves into the complex interplay between AR-driven precipitation, temperature, and snowpack, providing valuable insights into the precarious dynamics of California’s regional hydrology with a real-world example. Significance Statement The purpose of this study is to analyze the anomalous weather observed during the 2022–23 winter and its effects on California’s water resources. Specifically, we study precipitation, temperature, atmospheric rivers (ARs), drought, snowpack, and reservoir storage chronologically. We found that the high precipitation and low temperatures during the 2022–23 winter allowed California to reach a record-high snowpack and mitigated drought conditions. The 2022–23 wintertime precipitation was the highest since 2002 in Southern California. Fortunately, the low temperatures over the spring and summer helped slow the rate of snowpack melting and prevented significant flooding. This research contributes to a better understanding of the interplay between precipitation patterns, temperature changes, and AR events and offers insights into the dynamics of the hydrological cycle.