| With the background of global warming and intensifying human activities, the temperature, precipitation and runoff in the Bailong River basin present particular variations. Therefore, it is extremely important to analyze the variation characteristics of hydrometeorology elements, the relationship among temperature, precipitation and runoff, and the influence factors of runoff changes. This study is of great importance to guide the healthy development of ecological environment, the reasonable exploration and utilization of water resource, and the sustainable development of economy and society.This paper defines the upper reaches of Wu Du hydrological station in the Bailong River basin as the study area. The datasets used in this research include the monthly average temperature and precipitation time series measured by20meteorological stations of the study area, the monthly and annual runoff data measured by the Wu Du hydrological station from1961to2010. Firstly, the mathematical statistics was applied to study the intra-annual distributions of the temperature, precipitation and runoff. After that, the Mann-Kendall test, R/S analysis and complex Morlet wavelet analysis were used to analyze the seasonal and inter-annual variation characteristics, periodic regularity and persistence of the temperature, precipitation and runoff. Finally, the relationships among temperature, precipitation and runoff, and the impact of meteorological factors and human activities on the runoff change were discussed by the multiple linear regression analysis and double cumulative curve method respectively.The results showed that, the intra-annual distribution of the temperature was uneven in the past50years. The maximum temperature stably kept in July, and the temperature was over zero degrees Celsius between April and October. While, the minimum temperature maintained in January, and the temperature from March to November was below zero degrees Celsius. The distribution pattern of temperature within a year was basically stable as a whole. The intra-annual distribution of Ihe precipitation was not even, and the precipitation from April to October occupied94percent of the annual precipitation. The intra-annual inhomogeneity distribution, absolute amplitude and concentration of the precipitation had a decreasing trend, while the concentrated period of the precipitation had an advancing trend. The intra-annual distribution of the precipitation tended to be uniform gradually. The intra-annual distribution of the runoff was uneven either. The flood season from May to October occupied75percent of the total annual runoff, and the rest percent was for the non-flood season. The intra-annual inhomogeneity distribution of runoff decreased, as well as absolute amplitude and concentration. The concentrated period of the runoff had an advancing trend. The intra-annual distribution of the runoff tended to be uniform gradually.The seasonal and annual average temperature both showed a significant rising trend. According to the Mann-Kendall test of the temperature, it increased slowly before the mid1980s, but it began to accelerate and even had a warm mutation since1990s. With the R/S analysis to predict the future temperature change trend, the seasonal and annual average temperature would keep rising within a period time in the future. Based on the linear trend of the annual rainfall, it slightly decreased in the past50years and it experienced the’more-less-more-less’fluctuations. The precipitation had a decreasing trend in the spring and autumn, and it had an increasing trend in the summer and winter. As shown in the Mann-Kendall test, within the curve of confidence interval, both the seasonal and annual percipitation had several crossing points. Being verified, the percipitation showed no sudden change in the whole year except for the precipitation in the winter which suddenly went up from1972. In a period of a time in the future, the precipitation would increase in the summer and winter, and it would decrease in the spring and autumm, as well as the annual precipitation. The seasonal and annual runoff also decreased significantly. The annual runoff experienced a mutation in1990which indicated that annual runoff showed a significantly decreasing trend after1990. The decreasing trend of the seasonal and annual runoff would continue in the future. The temperature, percipitation and runoff had characteristics of multiple time scales. The periodic variations of the annual average temperature, annual percipitation and annual runoff were6-7a,12-13a and20a respectively.The runoff had a lag time in its response to the precipitation, and the hysteresis had a weak rising trend by the analysis of their concentrated period. Through the annual runoff coefficient analysis, it has been found that the runoff from precipitation decreased significantly with the time due to plant interception, infiltration and evaporation in recent50years. The runoff coefficient reduced to0.38from0.52after1990. The runoff had a significant positive and negative correlation with the temperature and precipitation by multiple linear regression analysis. Influence of precipitation on runoff was larger than the temperature. The decrease of the percipitation in the flood season and the rising temperature both caused the decrease of the runoff in the mid-upper reaches of the Bailing River basin. The runoff in the high values of sunspot activities was less than normal, while the runoff in the low values of sunspot activities was more than normal during1961-1985. The runoff both in the high and low values of sunspot activities was less than normal during1985-2010. The ENSO cycle had some influence on the runoff of the Bailong River basin. The annual runoff was sensitive to El Nino. When it occurred, the runoff decreased. In the next year when it did not occur, the runoff did not decrease as much as in the previous year. The annual runoff was not sensitive to La Nina.The result of double mass analysis showed that the variations of runoff in the studied area mainly attributed to human activities after1990, and its contribution was about80%. Before1990, precipitation was the dominant factor influencing runoff change with a contribution more than50%. The impact of hunman activities on the runoff change was mainly reflected in its contribution to the variations of the underlying suface and river diversion. |
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