LAUSR

Abstract The Antarctic Peninsula (AP) has recorded one of the strongest warming rates on the Earth since the 1950s, which, however, turned into a cooling trend since 1999. Snow liquid water emerges in the snowpacks in the AP during melt seasons. Monitoring snow liquid water on the AP is critical for evaluating its impacts on the stability, surface mass and energy balances of ice shelves. Most of our knowledge about the occurrence of snow liquid water (OLW) stems from satellite observations and model simulations. However, the relative performances of OLW products derived from these measurements have never been evaluated due to the lack of in-situ snow wetness measurements. We ranked the OLW determined by the radiometer (i.e., Special Sensor Microwave Imager), scatterometer (i.e., Quick Scatterometer and Advanced Scatterometer) and the Regional Atmospheric Circulation Model (RACMO2) based on categorical triple collocation (CTC) which can identify the most accurate observation with unknown true values. The CTC fusion product was generated by adopting the best source for each pixel during 1999–2017. The cumulative liquid water volume simulated by RACMO2 has significantly declined (at the 99% confidence level) by 210 Gt decade−1, while the decreasing trends in CTC-fused liquid water days (−1.18 days decade−1) and cumulative wet surface (−1.69 × 106 days km2 decade−1) were not statistically significant. The significantly negative trend in eastern AP snow liquid water agreed well with the simultaneous cooling, and may be linked with the increased adjacent sea ice.