Attributional comparative analysis of runoff and sediment change in typical basin of Loess Plateau

Abstract: In recent decades, the runoff and sediment of the Yellow River middle reaches located in the Loess Plateau have changed significantly. Many scholars have carried out a lot of researches on the Wuding River, a typical basin of the Loess Plateau, but these researches are focused on the breakthrough of methods and ignore the comparative analysis among methods. This study compared the difference of four methods, i.e., double cumulative curve method, hydrological method, elastic coefficient method and soil and water conservation method, to conduct attributional comparative analysis of runoff and sediment change in the Wuding River Basin from 1957 to 2010. Both double cumulative curve method and hydrological method separate the influence of climate change and human activity by substituting the precipitation data in the research period into the precipitation-runoff and precipitation-sediment transport relationships established in the reference period, and the hydrological method takes into account the annual distribution of precipitation. The elastic coefficient method generates runoff and sediment elasticities to quantify the effects of climate change and human activities. The soil and water conservation method refers to determining the runoff and sediment reduction indicators of each measure under different conditions and periods in different geomorphic areas. The results of trend and change point analysis showed that the annual precipitation in the Wuding River Basin has not changed significantly. The annual potential evaporation, annual runoff and annual sediment transport decreased significantly and the year of change point was 1982, 1971 and 1971, respectively. The attributional comparative analysis of runoff showed that the results of hydrological method were close to those of elastic coefficient method, and the contribution rate of human activities of soil and water conservation method was relatively small, and the attributional comparative analysis of sediment transport showed that the results of soil and water conservation method were consistent with those of the other three methods. Attribution analysis results indicated human activities were the dominant factor of runoff and sediment change in the basin, and their effects on runoff and sediment change were increasing year by year. Among different human activities, irrigation water diversion and afforestation played a leading role in runoff change, and check dam and afforestation played a leading role in sediment transport change. The full up or failure of check dam built in the 1970s and 1980s would largely weaken the runoff and sediment reduction benefits of water conservancy and soil conservation measures in the short term. In the long term, the impact of ecological construction, such as returning cultivated land to forestland or grassland, on runoff and sediment transport will gradually play a major role. Therefore, in the future, the governance of the Wuding River Basin should continue to implement the policy of conversion of cropland to forest and grassland, and strengthen the layout optimization and post-maintenance of engineering measures such as check dam.