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. Seasonal snow cover of the Northern Hemisphere (NH) is amajor factor in the global climate system, which makes snow cover animportant variable in climate models. Previously, substantial uncertaintieshave been reported in NH snow water equivalent (SWE) estimates. A recentbias-correction method significantly reduces the uncertainty of NH SWEestimation, which enables a more reliable analysis of the climate models'ability to describe the snow cover. We have intercompared NH SWE estimatesbetween CMIP6 (Coupled Model Intercomparison Project Phase 6) models andobservation-based SWE reference data north of 40∘ N for the period1982–2014 and analyzed with a regression approach whether model biases intemperature (T) and precipitation (P) could explain the model biases in SWE.We analyzed separately SWE in winter and SWE change rate in spring. For SWEreference data, we used bias-corrected SnowCCI data for non-mountainousregions and the mean of Brown, MERRA-2 and Crocus v7 data for themountainous regions. The SnowCCI SWE data are based on satellite passivemicrowave radiometer data and in situ snow depth data. The analysis showsthat CMIP6 models tend to overestimate SWE; however, large variabilityexists between models. In winter, P is the dominant factor causing SWEdiscrepancies especially in the northern and coastal regions. T contributesto SWE biases mainly in regions, where T is close to 0∘ C in winter.In spring, the importance of T in explaining the snowmelt rate discrepanciesincreases. This is to be expected, because the increase in T is the mainfactor that causes snow to melt as spring progresses. Furthermore, it isobvious from the results that biases in T or P cannot explain all modelbiases either in SWE in winter or in the snowmelt rate in spring. Otherfactors, such as deficiencies in model parameterizations and possibly biasesin the observational datasets, also contribute to SWE discrepancies. Inparticular, linear regression suggests that when the biases in T and P areeliminated, the models generally overestimate the snowmelt rate in spring.

Evaluation of Northern Hemisphere snow water equivalent in CMIP6 models during 1982–2014