Characteristic Of Climate And Runoff Of Main Rivers In Gansu During 1959-2006

Since 1987, there have been signals of the transition from warm-dry to warm-wet indicated in northwest of China.For example,the precipitation and glacier melt water had significant increases, river runoff increased sharply and vegetative cover improved significantly in the northern part of Xinjiang,Tianshan and its two-side zones,west of the Tarim basin,the lower reaches of Yarkant river,the western region of Qilian Mountain and its northern side.Yet evaporation decreased in some areas,.Nevertheless,the eastern Qilian Mountains and its east side had no transition with stable rainfall volume. The precipitation increased slightly in the Taklamakan desert,eastern part of Nanjiang,and west margin desert region,Gansu. But inside the Qaidam basin and other regions the precipitation increased slightly.Southeast of Qinghai province,Shanxi,Ningxia had little precipitation due to the East Asian monsoon.Shiyafeng(2003) reported that there was transformation features in climate in the western region of China.Some areas of transformation were not apparentpresented with persistent drought weather which could be attributed to many factors.This article analysed 1959-2006 climate, main river runoff of GanSu Province by EOF, REOF, M-K test, stepwise regression and other methods to make it clear the differences in Gansu province and the influence of temperature change on precipitationand the main factors of main rivers runoff and influence on its primary and secondary degree of changes were analysed,the results were as followed:1) During the period of 1959 to 2006, the precipitation of Gansu Province were obviously different from region to region,the east side was opposite to the west side,and there were also some differences in precipitation between south and north; precipitation of the east of Wushao Mountain presented an obvious downward trend, but in most parts of its west,there was an increase in different degrees,especially Yongchang,etc.2) From 1959 to 2006,Gansu Province got an overall good agreement in temperatureshift. Most part of the area showed a significant increase in the temperature after 1987;but some differences of the range of temperature changes in different regions of Gansu also occurred, compared with 1959-1986, from 1987 to 2006, more average temperature were rose in Northern Gansu, Hexi Corridor in the eastern and the east and west of Qilian Mountains;followed by the western Hexi Corridor and the central part of Qilian Mountains, but the southeastern Gansu was the lowest one.3) Different precipitation and temperature changes can produce different runoff. According to the contrast of it,we can see that,from 1987 to 2006,Shule and Heihe River had a sharply increased annual runoff; and Shiyang's trend was unapparent, generally, there was a reduction in total; while the annual runoff of Weihe River showed a significant decreasing trend;Shule and Heihe largely increased their monthly runoff in June, July and August, and Weihe River largely increased their monthly runoff in August and September, but Shiyang had a stable one.4)The annual runoff of Shule mainly depended on precipitation and temperature.In fact, there is a positive correlation between precipitation, temperature and runoff. With the increase in precipitation and temperature,annual runoff increased significantly in Shule;annual runoff of Heihe was mainly contributed by precipitation,of course the melting of seasonal snow caused by the spring temperature would increase the runoff at some level; Shiyang's annual runoff was sharply affected by precipitation but little by temperature,so that its runoff was stable;although the correlation between precipitation, temperature and runoff was obvious in Weihe Rive,runoff was negatively correlated with temperature.With the decrease in precipitation and increases in temperature,the runoff was significantly reduced.