PNNL

Abstract

Atmospheric rivers (ARs) can significantly modulate surface hydrological processes through the extreme precipitation they produce. Previous studies have investigated the impact of ARs on individual hydrological processes, but a comprehensive evaluation of ARs’ impact on surface hydrology is lacking. This study used a high-resolution regional climate simulation to quantify the impact of ARs on surface hydrological processes across the western U.S. watersheds. The model performance is evaluated through extensive comparison against observations. Our analysis indicates that ARs produce heavy precipitation but suppress evapotranspiration. Snowpack ablates more during ARs, which is mainly driven by warmer air temperature and increased downward longwave radiation. At the 0oC to 10oC temperature range, ARs increase the probability of snow ablation from 0.33 to 0.57. Soil moisture responds similarly to AR and non-AR precipitation events. The runoff-to-precipitation ratio almost doubles due to modulation by heavy precipitation in the southwestern watersheds or intensification of snow ablation in the northwestern watersheds during AR events compared to non-AR events. From analysis of the relationship between the hydrological responses and different meteorological factors, precipitation, temperature and radiation were identified as the key drivers that distinguish the hydrologic responses between AR and non-AR events. Lastly, analysis of ARs and total runoff at annual scale and April 1st snowpack and winter precipitation shows that ARs explain 30% to 60% of the interannual variance and sharpen the seasonality of water resources availability in the west coast mountain watersheds.