Multi-scale analysis on precipitation-runoff relationship in Chaobaihe Basin
Liu Jiakai, Zhang Zhenming, Yan Guoxin, Yu Xinxiao
(1. School of Nature Conservation, Beijing Forestry University, 100083, Beijing, China; 2. School of Soil and Water Conservation, Beijing Forestry University, 100083, Beijing, China)
[Background] Climate variations, especially the changes of precipitation are considered as a main factor of runoff decrease. However, previous studies reported that the feedback of runoff to the precipitation varied in different are as and time periods. It might be also influenced by the basins'scales. This work is to reveal the relationship between runoff and precipitation in different spatial-temporal scales in Chaobaihe Basin, the major water resource area for Beijing, from 1957 to 2001. [Methods] The climate data was from meteorological stations of China Meteorological Administration while the runoff data was from hydrological stations of Chaobaihe Basin. The precipitation series of each sub-basin were calculated by Thiessen polygon method, and Mann-Kendall trend test was used to identify the change trends and abrupt change points. At last, the relationship between precipitation-runoff were analyzed using regression analysis. [Results] The runoff change trend in each sub-basin was lightly different from each other,differing in the extent of fluctuations and degree of stability, however, the difference was not significant. According to the analysis of abrupt change points, the 44 years was divided into 3 periods:runoff increase period, decline period and stable period. The results suggested that the runoff decreased sharply from 1960 to 1970 and after 1990 the runoff increased slightly, while from 1970 to 1990,the runoff fluctuated greatly and did not show obvious rules. On the otherhand,based on the Pearson correlation coefficient from regression analysis between precipitation and runoff,the value became smaller as the sub-basin scale in creased. This meant that precipitation affected the small basins more significantly, and the affecting factors in the large basins were more complex. The larger the basin area was,the weaker the correlation between runoff and precipitation was. In addition, the relations also showed differences indifferent period. The Pearson correlation coefficients in increase and stable period were larger than that in the decrease period. This difference indicated that the responses of runoff to the precipitation in increase and stable period were much stronger than indecline period. Increase of runoff was deeply influenced by precipitation while the decrease of runoff was affected more by other factors. [Conclusions] Human activities and climate changes are two factors that influence the runoff. In Chaobaihe Basin and its sub-basins, increasing precipitation leads to the increase of runoff while human activities should be responsible for the runoff decreasing. Besides,in small-scale basins, precipitation variation could explain the change of runoff verywell, however in large-scale basins, human activities might be the main reason causing the changes of runoff. Thus, in order to guarantee the water yield, management of human activities such as optimization the land use and reasonable utilization of water resources is crucially important.