HAPpy Hour Seminar : Evaluation of CONUS404 cold-season precipitation and snowpack over the mountainous western United States

Abstract: In the western United States, water supply and availability remain highly dependent on cold-season snowfall and the seasonal snowpack. This study evaluates the ability of CONUS404, a 4 km resolution historical climate reconstruction that uses a coupled atmospheric-land surface model driven by a global reanalysis, to effectively simulate the precipitation 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 over the period of 1985 to 2021. Analysis was performed across four subdomains with distinct hydroclimates. Locations with a seasonal snowpack are isolated from those without. Other variables such as surface temperature and fraction of frozen precipitation are investigated to gain insight into apparent biases.

CONUS404 cold-season precipitation generally agrees well with gauge-based gridded data. CONUS404 SWE is similar to observationally based datasets during the early accumulation period, but CONUS404 consistently exhibits earlier-peaking, shallower snowpacks with slower ablation rates. CONUS404’s good agreement in terms of seasonal precipitation, SWE during the accumulation period (early in the cold season), and fraction of frozen precipitation (with a slight positive bias) seems to indicate that precipitation input is not the primary driver of CONUS404’s negative SWE bias that develops in the late cold season. Daily surface temperature maxima are low-biased, so they too do not explain this apparent SWE deficit. The apparent negative SWE bias may be due to a positive bias of the gridded observational datasets, ultimately because the SWE measured at SNOTEL sites may tend to overestimate the regional SWE in late winter/early spring.

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