Response of runoff to change of atmospheric 0°C level height in summer in arid region of Northwest China

Abstract

Based on the daily observed data from eight sounding stations and the daily mountain runoff data from nine rivers in summer from 1960 to 2009 in four typical study areas located in arid region of Northwest China (ARNC), the change trends, abrupt change points, and their significance of runoff and 0°C level height (FLH) were analyzed in ARNC in the last 50 years by using Mann-Kendall (MK) nonparametric test, and the quantitative relationship between runoff and FLH in summer was also analyzed with the linear regression and elastic coefficient methods. The results are indicated as follows: (1) in recent 50 years, there is a similar changing trend between the summer runoff and FLH in ARNC and each region has its own unique feature. The summer runoff has been significantly ascending in the Tianshan Mountains and on the northern slope of the Qilian Mountains (NSQM) compared to that of the northern slope of the Kunlun Mountains (NSKM). Likewise, the FLH has been taking on a markedly rising trend on the northern slopes of the Tianshan and Qilian Mountains (NSTM and NSQM) in comparison with the southern slope of the Tianshan Mountains (SSTM). However, the FLH on NSKM has been decreasing with the speed of 2.33 m every year. (2) Abrupt change analysis indicates that the period of abrupt change happened for summer runoff and FLH is totally different among the four typical study regions, and even in same region. (3) There is a positive significant relation between the summer runoff and FLH in ARNC (NSQM P <0.05; other three regions P <0.01). Therefore, the ascending and descending of the summer FLH is a vital factor inducing the change of summer runoff in ARNC. (4) The elastic coefficient of summer runoff to the change of summer FLH on NSKM, NSTM, NSQM, and SSTM are 7.19, 3.80, 2.79, and 6.63, respectively, which indicates that there exists the regional difference in the sensibility of summer runoff to the change of summer FLH in ARNC. The distinct proportion of glacial meltwater runoff is an important cause resulting in the regional difference of sensibility.