Precipitation biases and snow physics limitations drive the uncertainties in macroscale modeled snow water equivalent

[摘要] Seasonal snow is an essential component of regional and globalwater and energy cycles, particularly in snow-dominant regions that rely onsnowmelt for water resources. Land surface models (LSMs) are a commonapproach for developing spatially and temporally complete estimates of snowwater equivalent (SWE) and hydrologic variables at a large scale. However,the accuracy of the LSM-based SWE outputs is limited and unclear by mixedfactors such as uncertainties in the meteorological boundary conditions andthe model physics. In this study, we assess the SWE, snowfall,precipitation, and air temperature products from a 12-member ensemble –with four LSMs and three meteorological forcings – using automated SWE,precipitation, and temperature observations from 809 Snowpack Telemetrystations over the western US. Results show that the mean annual maximum LSMSWE is underestimated by 268 mm. The timing of peak SWE from the LSMs is on average 36 d earlier than that of the observations. By the date of peakSWE, winter accumulated precipitation is underestimated (forcings mean: 485mm vs. stations: 690 mm). In addition, the precipitation partitioningphysics generates different snowfall estimates by an average of 113 mm with the same forcing data. Even though there are widespread cold biases (up to 3  ∘ C) in the temperature forcings, larger ablations and lower ratios of SWE to total precipitation are found even in the accumulation period, indicating that melting physics in LSMs drives some SWE uncertainties. Based on the principal component analysis, we find thatprecipitation bias and partitioning methods have a large contribution to the first principal component, which accounts for about half of the totalvariance. The results provide insights into prioritizing strategies toimprove SWE estimates from LSMs for hydrologic applications.

[学科分类] 妇产科学