Climate Change Spatiotemporal Features And Impacton Hydrological Process In Northwest Arid Area Of China

Climate change has been a global issue and it has been proved true that the temperature is increasing with regional variations. The study of long time meteorological data series can guide the study of character, mechanism and the evaluation of the future climate. The arid region of China is characterized by low precipitation, long duration of sunshine and strong evaporation, making this area an ecological fragile region and has long been concerned. Meanwhile it is influenced by the global climate change due to its special location and in turn affects the global climate change.In this article, the daily temperature and precipitation data along with the hydrological data was analyzed, in conjunction with the snow cover area charts from the MODIS satellites (MOD1OAl) in order to study the climate change and hydrology in the arid area in the northwest China.The research results indicate that:(1) The arid region of northwest China has gone through from warm-dry condition to warm-wet condition in the past50yr, and the changing rates of temperature and precipitation are0.37℃/10a,6.5mm/10a. In addition, the change of temperature is much more significant than precipitation. The spatial character of temperature change can be summed up as the higher the latitude is, the higher the elevation is, the faster the increasing is, and further the former has greater influence. In the study area, the northern area of Tianshan Mountain has seen the faster increase of temperature than the southern part and the mountainous area has a more intense increase than the plain area. The current climate change tendency will be continuous in the future based on the Hurst index. The temperature change tendencies are alike in the four typical basins and the temperature catastrophe points happened in1996. Only Aksu River and Kaidu River show increasing trends in precipitation and Yarkand River and Hotan River show no changing tendency.(2) By studying the runoff changing characters of the headrivers, the catastrophe points of runoffs of Aksu River and Kaidu River happened in1990and1996. the runoff of Yarkand River increased, but the tendency does not significant, and Hotan River turns out to be the only river that has a decreased runoff.Periodic analysis by using the wavelet transform and wavelet variances analysis confirms that the melting water in the Aksu River basin contributes a lot to the runoff in another side. The results also manifest that the runoffs of Yarkand River and Hotan River are more sensitive to precipitation while the increased runoff of Kaidu River is the combined impact of increasing temperature and precipitation.(3) Most of the cold indexes are in downward tendencies while the warm indexes in upward tendencies as a whole in the past50years. In addition, rate of change of the extreme temperature after2000is higher than before and its frequency is becoming stable.Number of wet days is decreasing significantly while the annual precipitation is increasing evidently in the arid area of northwest China. The decrease is mainly caused by the sharp decrease of days of0.1～6mm precipitation. The heavy precipitation contributes a lot to the annual precipitation, especially the heavy precipitation intensity between12-24mm and between6-12mm.The extremes of runoff were sensitive to the changes of extreme temperature and precipitation. Times of short term flood peak increased, and it was caused by the change of extreme temperature in Aksu River basin, but it is due to the fluctuation of extreme precipitation in the Yarkand River. That change was not significant in Hotan River and Kaidu River.(4) The snow-cover area shows an increasing tendency during February to April and August to October and a decreasing tendency from May to August and from October to the following January using the MODIS data in the mountainous regions in the Tarim River basin. The snow line of the southern slope of the Tianshan Mountain is4200m, while the height reaches5800m in the northern slope of Kunlun mountain. Contrastive analysis of the10-days combined snow cover extent charts and the precipitation and runoff data manifests that flood peak is caused by the combined action of snow melting below the snow line (for the southern slope of Tianshan mountain, the elevation is4200m; the northern slope of Kunlun Mountain, it is5800m) and the precipitation increasing; while, above the snow line, the melt water is mainly used for recharging the groundwater and in turn maintain the runoff in the dry season.