Orientation dependent glacial changes at the Tibetan Plateau derived from 2003–2009 ICESat laser altimetry

Abstract. Monitoring glacier changes is essential for estimating the water mass balance of the Tibetan Plateau. Recent research indicated that glaciers at individual regions on the Tibetan Plateau and surroundings are shrinking and thinning during the last decades. Studies considering large regions often ignored however impact of locally varying weather conditions and terrain characteristics on glacial evolution, due to orographic precipitation and variation in solar radiation. Our hypothesis is therefore that adjacent glaciers of opposite orientation change in a different way. In this study, we exploit ICESat laser altimetry data in combination with the SRTM DEM and the GLIMS glacier mask to estimate glacial vertical change trends between 2003 and 2009 on the whole Tibetan Plateau. Considering acquisition conditions of ICESat measurements and terrain surface characteristics, annual glacial elevation trends were estimated for 15 different settings. In the final setting, we only include ICESat elevations acquired over terrain that has a slope of below 20° and a roughness at the footprint scale of below 15 m. Within this setting, 90 glacial areas could be distinguished. The results show that most of observed glacial areas on the Tibetan Plateau are thinning, except for notably glaciers in the Northwest. In general, glacial elevations on the whole Tibetan Plateau decreased at an average rate of −0.17 ± 0.47 m per year (m a⁻¹) between 2003 and 2009, but note that the size, distribution, and representativeness of the observed glacial areas are not taken into account. Moreover, the results show that glacial elevation changes indeed strongly depend on the relative position in a mountain range.