Seasonal Variations and Drought in the Green River Basin, Wyoming

Abstract

Climate change continues to exacerbate hydrologic stress on the Western United States. Roughly 50 million Americans rely on water from the Colorado River Basin. The Colorado River Basin has experienced flow reductions from 2000-2014 averaging 19.3% below 20th century averages, with at least a third of this being directly due to climate change. We assessed climate conditions associated with severe drought in the northernmost headwaters of the Colorado River, Wyoming's Green River basin. Data from NOAA/NCEI climate division database were used to create annual time series to determine long-term averages and subsequently identify anomalous drought years in the basin. Data from the North American Regional Reanalysis (NARR) was then used to create composite-anomaly maps for the following variables: Precipitation (at surface) Geopotential Height (500mb), Specific Humidity (850mb), Omega (500mb), Vector Winds (500mb), and Temperature (at surface). The years with the most significant drier-than-average conditions (1988, 2001, 2002, 2012, 2020) included intra-annual variability across seasons with three of the five driest years exhibiting normal or wetter-than-normal winter conditions. All selected drought years exhibited consistent warmer-than-normal and drier-than-normal spring and summer conditions supporting persistent drought conditions. Review of specific humidity and geopotential height conditions for these seasons during the drier-than-normal years indicated significantly lower-than-average values (specific humidity at 850mb), as well as persistent anomalous higher-than-average atmospheric pressure (geopotential height at 500mb).