Attribution Analysis Of Runoff Variation In Typical Catchments Of The Loess Plateau Based On Budyko Hypothesis

For nearly half a century,dramatic changes in climatic factors and underlying conditions have had a major impact on the catchments'hydrological cycle.With the improvement of the ecological system in the Loess Plateau,the annual runoff and sediment volume of the Yellow River has decreased sharply.Studying river runoff changes and its attribution analysis is of great significance for watershed management and soil and water conservation.To this end,this study used Mann-Kandall trend test,Pettitt mutation test,double cumulative curve and other methods to study the runoff variation of three typical basins in the Yellow River Helong section?Huangfuchuan Basin,Wuding River Basin and Yanhe River Basin?.Based on the Budyko hypothesis,quantitatively assess the extent to which climate and underlying surface changes affect runoff changes.The main conclusions are as follows:?1?The interannual variation trend of precipitation and potential evaporation in basins was not significant,while the runoff showed a significant downward trend with obvious stage and abrupt characteristics.The MK trend test statistic of precipitation and potential evaporation in the three basins did not reach a significant level,while the runoff reached a significant decline.we can see that there is a catastrophe point in the Huangfuchuan Basin,which is 1996;there are two mutation points in the Wuding River Basin,in 1971.And in 1996,the Yanhe River Basin had a mutation point for 1996.?2?The runoff depth of basins is more sensitive to the underlying surface parameters than the climatic factors,and the complement method calculates the runoff depth with the highest accuracy.The mean values of the sensitivity of the three runoff depths R to?,P and ET₀ were-3.52,2.61 and-1.62,respectively.Attribution analysis of runoff variation in three basins by means of total differential method and complementary method showed that underlying surface changes in different basins were the dominant factors of runoff variation;the influence of underlying surface changes on runoff reduction in Huangfuchuan Basin was 88%,the contribution of the underlying surface change to runoff during the period from1997 to 2016 in the Wuding River Basin was 61%,and the impact of the underlying surface change on the runoff in the Yanhe River Basin was 37%;the“two-stage average”method was used to calculate the total differential method.The relative error between the runoff variation and the actual observation values of the three basins is 13.52%,1.74%and 0.44%,respectively.The characteristics of the total differential method,the complementary method,the decomposition method and the extrapolation method are complementary.The method is the best way to calculate attribution analysis.?3?The underlying surface parameters of the three watersheds are less sensitive to the seasonal climate index than that of vegetation coverage.The seasonal climate index of the three basins show no significant interannual variability,and the vegetation coverage showed a significant upward trend.All the annual dryness index and evapotranspiration rate of each watershed were concentrated around the Budyko curve,and the parameter?was in.The sensitivity coefficients of the parameter?to the climatic seasonal index S in the Huangfuchuan,Wuding river and Yanhe river basin are-0.04,-0.05,-0.03,respectively,and the sensitivity coefficients to vegetation coverage are 0.24,0.29,and 0.31,respectively.It is indicated that among the factors affecting the runoff variation in the Wuding River Basin and the Huangfuchuan Basin,factors such as human activities,soil conditions and terrain slope have contributed a lot.In addition to changes in climate and underlying surface,changes in water storage in the basin also contribute to changes in runoff.In recent years,returning farmland to forests and soil and water conservation measures have played a significant role in reducing runoff.