ANALYSIS OF CHARACTERISTICS OF PRECIPITATION AND RUNOFF IN THE TYPICAL KARST CATCHMENT AND CONTRIBUTION DECOMPOSITION ON INFLUENCING FACTORS OF INTERANNUAL RUNOFF VARIATION
The research of underground hydrological process plays an important role in the scientific research of the critical zone on the Earth. The hydrological process in karst landscapes with double porosity system is different from other regions. Investigating the characteristics of precipitation and runoff and analyzing the influencing factors of the runoff interannual variation will help to understand the hydrological characteristics of karst catchment to the climate change and human activities in the regional perspective. The studied area (26°12'26"~26°17'20"N,105°40'38"~ 105°48'13"E), the Houzhai catchment, is located in southern of Puding County, Guizhou Province, which has a total area of 81 km2. Two streams, including the surface river and subterranean river flow at the northwest of this catchment, were studied. In this paper, the seasonal and interannual change characteristics of precipitation and runoff had been analyzed, and the concentration degree and unevenness coefficient indices were employed to analyze the temporal trend of seasonal precipitation and runoff distribution of the catchment based on the precipitation and runoff monthly time series observed data of Houzhai hydrological station in 1987 ~2006. The results indicated that: (1) The response of surface runoff and subterranean runoff to precipitation has lagged effect at the seasonal scale under the impacts of rain intensity,the surface soil moisture level,subterranean structure and agricultural activities used water; (2) Both surface runoff and subterranean runoff are largely affected by non-precipitation factors,what's more,the surface runoff is severely affected in the interannual; (3) The concentration and nonuniformity of subterranean runoff are more affected by precipitation than surface runoff, however, the concentration and nonuniformity is lower due to the subterranean fissure and conduit. The methods of cumulative anomaly and interannual accumulation were used to analyze the precipitation and runoff sequence interannual trend of Houzhai catchment over nearly 20 years, so as to identify the two turning points of 1990 and 2002, of which 1990 was the year of inflection point. The revised slope change ratio of cumulative quantity was used to calculate quantitatively the contribution rate of the precipitation, potential evapotranspiration and human activities to surface and subterranean runoff interannual variation. Take the year of inflection point as a boundary, the period of 1987 ~ 1990 (T_1) is regarded as the base period that represents less effect period by human activities. With the increase of human activities, the period of 1991 ~2002 (T2) can be regarded as the measure period that represents more effect period by human activities. The results demonstrated that: (1) Without considering the influence of evapotranspiration in the area, the contribution rate of precipitation reduction to surface runoff and subterranean runoff decrease were 39.32% and 46.52% respectively in the period of T_2 compared with the base period T_1 (1987 ~1990),while the contribution rate of human activities to the surface runoff and subterranean runoff reduction were 60.68% and 53.48% respectively; (2) On the contrary, with considering the influence of potential evapotranspiration,the contribution rate of potential evapotranspiration reduction to the surface runoff and underground runoff decrease were -14.89% and -17.61% respectively in the period of T_2,and the contribution rate of human activities to the surface runoff and subterranean runoff were increased to 75.57% and 71.09% respectively. Obviously, human activity was the dominant factor impacting the runoff yield interannual changes of the Houzhai catchment.