Evaluation of CONUS404 Cold-Season Precipitation and Snowpack over the Mountainous Western United States

This study evaluates the ability of CONUS404, a 4-km resolution historical climate reconstruction that uses a coupled atmosphere-land surface model driven by a global reanalysis, to accurately simulate the precipitation, temperature, and snow water equivalent (SWE) across the mountainous western United States by comparing it against a variety of datasets including observations, statistical interpolations, and data assimilation products. The analysis was performed across four subdomains with distinct hydroclimates over the period from 1985 to 2021. CONUS404 cold-season precipitation generally agrees well with gauge-based gridded estimates, with some exceptions. CONUS404 matches observationally based SWE estimates during the early accumulation period but consistently exhibits earlier-peaking, shallower snowpacks with slower late-season ablation rates. CONUS404's good agreement in terms of seasonal precipitation and SWE during the accumulation period (early in the cold season) suggests that snowfall is not the primary driver of CONUS404's negative SWE bias that begins to emerge in January. While the average temperatures are a fairly good representation, CONUS404 cannot adequately simulate the full extent of nighttime cold temperatures (minima are warm biased) or daytime warm temperatures (maxima are cold biased), resulting in a significantly reduced daily temperature range. This study cannot fully attribute the cause of the negative SWE bias in CONUS404 in late winter, and further investigation is required.