Satellite observed spatiotemporal variability of snow cover and snow phenology over high mountain Asia from 2002 to 2021

• A synthetic analysis for spatiotemporal variability of snow cover and snow phenology was performed. • Decline of snow cover over the most of High Mountain Asia (HMA) from the hydrological year 2002–2020 was found. • The spatiotemporal variations of snow phenology have strong altitude dependence. • Air temperature was the dominant factor affecting the interannual variation of snow phenology. Accurate understanding the spatiotemporal variability of snow cover and snow phenology over High Mountain Asia (HMA) is of great interest because of their vital impacts on the hydrological processes, global climate system and regional water resource management. This study investigates the spatiotemporal variability of snow-covered extent (SCE), snow-covered days (SCD), snow onset date (SOD), snow end date (SED) and snow duration days (SDD) of HMA using the daily cloud-free Moderate Resolution Imaging Spectroradiometer (MODIS) snow cover products from the hydrological year 2002 to 2020. The vertical difference of the effect of elevation on snow phenology and the response of snow phenology to climate change are explored. The results indicate that the monthly SCE over the whole HMA exhibited a slight decreasing in most months over the study period. The variability of snow cover and snow phenology over the whole HMA generally showed decreased SCD (significant decrease accounts for 15.73%), delayed SOD (significant delay accounts for 14.35%), advanced SED (significant advance accounts for 15.46%) and shortened SDD (significant shorten accounts for 16.01%). It is worth noting that the snow cover in the West Himalaya was enhancing with its increased SCE, increased SCD and lengthened SDD. There is an elevation dependence of snow phenology changes over HMA with the high-altitude mountain ranges generally having a higher SCD, earlier SOD, later SED and longer SDD than low altitude areas. The air temperature of snow accumulation period is the dominant factor affecting the interannual variation of SOD, and the air temperature of snow melt period is the dominant factor affecting the interannual variation of SED. The increase of air temperature leads to the delayed SOD, advanced SED and shortened SDD.