Temperature trends and elevation dependent warming during 1965 – 2014 in headwaters of Yangtze River, Qinghai Tibetan Plateau

The understanding of temperature trends in high elevation mountain areas is an integral part of climate change research and it is critical for assessing the impacts of climate change on water resources including glacier melt, degradation of soils, and active layer thickness. In this study, climate changes were analyzed based on trends in air temperature variables(Tmax, Tmin, Tmean), and Diurnal Temperature Range(DTR) as well as elevation-dependent warming at annual and seasonal scales in the Headwaters of Yangtze River(HWYZ), Qinghai Tibetan Plateau. The Base Period(1965-2014) was split into two subperiods; Period-Ⅰ(1965-1989) and Period-Ⅱ(1990-2014) and the analysis was constrained over two subbasins; Zhimenda and Tuotuohe. Increasing trends were found in absolute changes in temperature variables during Period-Ⅱ as compared to Period-Ⅰ.Tmax, Tmin, and Tmeanhad significant increasing trends for both sub-basins. The highest significant trends in annual time scale were observed in Tmin(1.15℃ decade-1) in Tuotuohe and 0.98℃ decade-1in Zhimenda sub-basins. In Period-Ⅱ, only the winter season had the highest magnitudes of Tmaxand Tmin0.58℃ decade-1and 1.26℃ decade-1in Tuotuohe subbasin, respectively. Elevation dependent warming analysis revealed that Tmax, Tminand Tmeantrend magnitudes increase with the increase of elevations in the middle reaches(4000 m to 4400 m) of the HWYZ during Period-Ⅱ annually. The increasing trend magnitude during Period-Ⅱ, for Tmax, is 1.77, 0.92, and 1.31℃ decade-1, for Tmin1.20, 1.32 and 1.59℃ decade-1,for Tmean1.51, 1.10 and 1.51℃ decade-1at elevations of4066 m, 4175 m and 4415 m respectively in the winter season. Tmeanincreases during the spring season for> 3681 m elevations during Period-Ⅱ, with no particular relation with elevation dependency for other variables. During the summer season in Period Ⅱ, Tmax, Tmin, Tmeanincreases with the increase of elevations(3681 m to 4415 m) in the middle reaches of HWYZ. Elevation dependent warming(EDW), the study concluded that magnitudes of Tminare increasing significantly after the 1990s as compared to Tmaxin the HWYZ. It is concluded that the climate of the HWYZ is getting warmer in both sub-basins and the rate of warming was more evident after the 1990s. The outcomes of the study provide an essential insight into climate change in the region and would be a primary index to select and design research scenarios to explore the impacts of climate change on water resources.