Reconstruction of surface air temperature in a glaciated region in the western Qilian Mountains, Tibetan Plateau, 1957–2013 and its variation characteristics

Based on the meteorological observations at three sites (4180 m, 4550 m and 5040 m a.s.l.) in Laohugou and the surrounding 7 national meteorological stations, the long-term surface air temperature of the glaciated region in the Qilian Mountains, northeastern Tibetan Plateau during 1957–2013 was reconstructed. The in-situ air temperature observed at 4180 m during 1959–1961 was used to verify the reconstructed temperature series. Several approaches of multiple regressions were applied to select the optimal method in estimating the daily air temperature, including the ordinary least square regression (OLSR), stepwise regression (SR), principal component regression (PCR) and partial least squares regression (PLSR), respectively. According to root mean square error, mean bias error, and correlation coefficient, OLSR is selected as the optimal approach in the study region. The reconstructed daily temperature correlates well with the synchronous observations, and correlation coefficients are higher than 0.96 (p < 0.01) on an annual basis. All the three sites in the study region have experienced a warming trend, and annual mean temperature has increased by 0.31 C°, 0.35 C° and 0.37 C° per decade at 4180 m, 4550 m and 5040 m (p < 0.01), respectively. The higher elevations usually have larger trend magnitudes, compared with the lower sites. The positive degree day (PDD, the sum of daily mean temperatures above ice point) has significantly increased by 27.8 C°, 12.8 C°, and 3.2 C° per decade at 4180 m, 4550 m and 5040 m, respectively, which also indicates the continuing shrinkage of glaciers for the study region.