The increasing snow cover in the Amur River Basin from MODIS observations during 2000–2014

Abstract. The study applies the improved cloud-free Moderate Resolution Imaging Spectral radiometer (MODIS) daily snow cover product (MODMYD_MC) to analyze the snow cover variations from snow Hydrologic Year (HY) HY2000 to HY2013 in the Amur River Basin (ARB), northeast Asia. The fractions of forest cover were 38 %, 63 % and 47 % in 2009 in China (the southern ARB), Russia (the northern ARB) and ARB, respectively. Forest demonstrates complex influences on the snow accumulation and melting processes and on optical satellite snow cover mapping. Validation results show that MODMYD_MC has a snow agreement of 88 % against in situ snow depth (SD) observations (SD≥4cm). The agreement is about 10 % lower at the forested stations than at the non-forested stations. Snow Cover Durations (SCD) from MODMYD_MC are 20 days shorter than ground observations (SD ≥ 1 cm) at the forested stations, while they are just 8 days shorter than ground observations (SD ≥ 1 cm) at the non-forested stations. Annual mean SCDs in the forested areas are 21 days shorter than those in the nearby farmland in the SanJiang Plain. SCD and Snow Cover Fraction (SCF) are negatively correlated with air temperature in ARB, especially in the snow melting season, when the mean air temperature in March and April can explain 86 % and 74 % of the mean SCF variations in China and Russia, respectively. From 1961 to 2015, the annual mean air temperature presented an increase trend by 0.33 ℃/decade in both China and Russia, while it had a decrease trend during the study period from HY2000 to HY2013. The decrease of air temperature resulted in an increase of snow cover although the increase of snow cover was not significant above the 90 % confidence level. SCD and SCF had larger increase rates in China than in Russia, and they were larger in the forested area than in the nearby farmland in similarly climatic settings in the SanJiang Plain. Air temperature began to increase again in 2014 and 2015, and the increasing air temperature in ARB projects a decrease of snow cover extent and periods in the coming years.