Glacier surface elevation changes in Rongbuk Catchment of the Central Himalayas in the last four decades

Glaciers in the central Himalayas are important water resources for the downstream habitants, and accelerating melting of the high mountain glaciers speed up with continuous warming. We summerized the geodetic glacier surface elevation changes (Dh) by 6 data sets at different time periods during 1974-2016 in RongbukCatchment(RC) on the northern slope of Mt. Qomolangma (Mt. Everest) in the Central Himalayas. The result showed that glacier Dh varied with altitude and time, from -0.29 ± 0.03m a^-1 in 1974-2000, to -0.47 ±0.24 m a^-1 in 1974-2006,and -0.48 ±0.16 m a^-1 in 1974-2012. Dh increased to -0.60 ± 0.20 m a^-1 in 2000-2012, then decreased to-0.46 ± 0.24 m a^-1 in 2000-2014, and by -0.49 ± 0.08 m a^-1 in 2000-2016, showing a diverse rate being up - down- a little up. However, it generally presented a similar glacier thinning rate by -0.46~-0.49 m a^-1 in the last four decades since 1970s in RC according to Dh_1974-2006, Dh_1974-2012, Dh_2000-2014, and Dh_2000-2016. Local meteorological observations revealed that, to a first order, the glacier thinning rate was kept the same pace with the number of annual melting days (MD). In spite of the obviously arising summer air temperature (T_S) in 2000-2014, a slowdown glacier melting rate by -391 mm w.e.a^-1 occurred in 2000-2014 because of less melting days with more precipitation and less annual mean temperature(T_m). It shows that MD is another important indicator and controlling factor to evaluate or to estimate glacier melting trend, especially in hydrological or climate modeling.