04 Jan 2023
04 Jan 2023
Status: this preprint is currently under review for the journal TC.

Changes in March mean snow water equivalent since the mid-twentieth century and the contributing factors in reanalyses and CMIP6 climate models

Jouni Räisänen Jouni Räisänen
  • Institute for Atmospheric and Earth System Research/Physics, University of Helsinki, P.O. Box 64, FI-00014 University of Helsinki, Finland

Abstract. Trends in March mean snow water equivalent (SWE) in the Northern Hemisphere are attributed to changes in three main factors: total precipitation (P), fraction of precipitation as snowfall (F), and fraction of accumulated snowfall remaining on ground (G). This is repeated for two reanalyses (ERA5-Land from March 1951 to 2022 and MERRA2 from 1981 to 2022) and simulations by 22 climate models from the 6th phase of the Coupled Model Intercomparison Project (CMIP6). The results reveal a decrease in SWE in most of the Northern Hemisphere, as decreases in F and G dominate over mostly positive trends in P. However, there is spatial variability in both the magnitude and sign of these trends. There is substantial variation between the individual CMIP6 models, but the agreement between the CMIP6 multi-model mean and ERA5-Land is reasonable for both the area means and the geographical distribution of the trends from 1951 to 2022, with a spatial correlation of 0.51 for the total SWE trend. The agreement for the trends from 1981 to 2022 is worse, probably partly due to internal climate variability but also due to the overestimation of the recent warming in the CMIP6 models. Over this shorter period for which ERA5-Land can be compared with MERRA2, there are also marked trend differences between these two reanalyses. However, the SWE decreases associated with reduced snowfall fraction (F) are more consistent between the different data sets than the trends resulting from changes in P and G.

Jouni Räisänen

Status: open (until 01 Mar 2023)

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Jouni Räisänen

Data sets

Data and GrADS scripts for “Changes in March mean snow water equivalent since the mid-twentieth century and the contributing factors in reanalyses and CMIP6 climate models”, submitted to The Cryosphere Jouni Räisänen

Jouni Räisänen


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Short summary
Changes in snow amount since the mid-20th century are studied, focusing on the mechanisms that have changed the water equivalent of the snowpack (SWE). Both reanalysis and climate model data show a decrease in SWE in most of the Northern Hemisphere. The total winter precipitation has increased in most areas, but this has been compensated by reduced snowfall-to-precipitation ratio and enhanced snowmelt. However, the details and magnitude of these trends vary between different data sets.