Spatiotemporal distribution of snow in eastern Tibet and the response to climate change

Abstract

The spatial and temporal distribution of snow and its response to changes in climate were investigated from 1979 to 2005 in eastern Tibet. The Lhasa River basin, Niyang River basin and Changdu region cover an area of approximately 15×104km2 and ranges in elevation from 2000 to more than 7000m. This large area necessitates innovative procedures for estimating potential spatial and temporal changes in snow cover. For this analysis we used the microwave long-term snow cover dataset of China with a spatial resolution of 25km and temporal resolution of 1day. After data validation between the microwave dataset and MODIS snow product, we defined two parameters for each pixel: (1) median date of the snow-free period (Tm); and (2) duration of the snow-free period (ΔT). After removing transient-snow dominated areas, we find that the duration of the snow-free period was inversely correlated with elevation (R=−0.651, p<0.001). TFPW-MK (Trend-free pre-whitening Mann–Kendall) was then used to examine and highlight the trend of ΔT with time. At lower-elevation sites, the length of the snow-free season increased. In contrast, at higher-elevations, it decreased. Mann–Kendall tests on monthly air temperature and annual precipitation for the period 1979 to 2005 from seven climate stations in the region operated by the China Meteorological Data Sharing Service System show a significant increase in annual precipitation and an increase in monthly air temperatures for the fall through spring months. Thus, the length of the snow covered season appears to be decreasing at lower elevation because of the increase in air temperatures. However, at higher elevations the increase in precipitation appears to compensate for the increase in air temperature such that the snow-free period has decreased.