Investigating spatiotemporal patterns of snowline altitude at the end of melting season in High Mountain Asia, using cloud-free MODIS snow cover product, 2001–2016

Abstract. The snowline altitude at the end of melting season (SLA-EMS) can be used as an indicator of the equilibrium line altitude (ELA) and therefore for the annual mass balance of glaciers in certain conditions. High Mountain Asia (HMA) hosts the largest glacier and perennial snow cover concentration outside the polar regions, but the spatiotemporal pattern of SLA-EMS under climate change is poorly understood in there. Here, we develop a method for estimating SLA-EMS over large-scale area by using the cloud-removed MODIS fractional snow cover data, and investigate the spatiotemporal characteristics and trends of SLA-EMS during 2001–2016 over the HMA. The possible linkage between the SLA-EMS and temperature and precipitation changes over the HMA is also investigated. The results are as follows: (1) There are good linear regression relationships (R = −0.66) between the extracted grid (30 km) SLA-EMS and glaciers annual mass balance over the HMA. (2) Generally, the SLA-EMS in the HMA decreases with increase of latitude. And due to the mass elevation effect, it decreases from the high altitude region of Himalayas and inner Tibet to surrounding low mountainous area. (3) The SLA-EMS of HMA generally shows a rising trend in the recent years (2001–2016). In total, 75.3 % (24.2 % with a significant increase) and 16.1 % (less than 1 % with a significant decrease) of the study area show increasing and decreasing trends in SLA-EMS, respectively. The SLA-EMS significant increases in Tien Shan, Inner Tibet, south and east Tibet, east Himalaya and Hengduan Shan. (4) Temperature (especially the summer temperature) trends to be the dominant climatic factor affecting the variations of SLA-EMS over the HMA. Under the background of the generally losing glaciers mass in HMA, if the SLA-EMS continues to rise as a result of global warming, it will accelerate the negative mass balances of the glaciers. This study is an important step towards reconstruction the time series of glacier annual mass balance using SLA-EMS datasets at the scale of HMA to better document the relationships between climate and glaciers.