Trend of the Climate Changes in Dry Valleys of Hengduan Mountains, China

A long period of meteorological data collected at 20 typical meteorological observation stations scattered in dry valleys of the Hengduan Mountains, including monthly air temperature, precipitation, relative humidity, sunshine hours, highest air temperature and lowest air temperature, were cited for analysis of trend of the climate changes in the region, using the linear tendency estimation, Mann-Kendall test, precipitation concentration degree (PCD) and precipitation concentration period (PCP) methods. Results show that (1) affected by the global climate change, the mean air temperature in the dry valleys presented generally a rising trend with a rate of 0.11℃•(10a)^-1 , a bit lower than the rate 0.15℃•(10a) ^-1of the whole Hengduan Mountains and it was more obvious in in winter than in other seasons; (2) the mean air temperature in Yuanmou, Dongchuan and Qiaojia Valleys in the downstreams of the Jinsha River displayed a declining trend, more obvious in spring; (3) the precipitation in the dry valleys dropped slightly, by1.48mm•(10a)^-1, which is mainly attributed to the reduction of precipitation in summer, which was more obvious than that in other seasons; (4) annual precipitation in most of the dry valleys weakened in PCD, but temporally advanced in PCP, though not so obvious; and (5) relative humidity and sunshine hours presented a declining trend in recent decades. The former decreased at a rate of 0.16%•(10a)^-1 and the latter at a rate of 24.26h•(10a)^-1.