Attribution of runoff changes in the Hanjiang River basin based on Budyko hypothesis
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Abstract:
In recent decades,global climate change,especially anthropogenic activities such as land use change and reservoir construction have led to profound changes in hydrological processes in basins.Therefore,runoff change and attribution analysis under changing environment have become a hot research area among domestic and overseas scholars .The elastic coefficient method based on Budyko hypothesis is an effective method for the attribution analysis of runoff change,but its calculation results have some errors.Therefore,the Hanjiang River basin,which is sensitive to climate change and where human activities are intense is selected as the research object.The contribution rate of climate change and underlying surface change to runoff variability was quantitatively decomposed by the complementary relationship method of Budyko hypothesis,to provide a scientific basis for water resources management and sustainable utilization. The linear trend estimation and the moving average method were used to analyze the change trends of hydrometeorological elements at Baihe and Shayang stations in the Hanjiang River basin based on the hydrometeorological data such as temperature,precipitation and runoff from 1964 to 2015.Mann-Kendall test and Pettitt test were used to detect the abrupt change points in the annual runoff series at two stations.Based on Budyko′shydro-thermal coupling equilibrium theory,the elastic coefficients of runoff were calculated,and the complementary relationship method was used to quantitatively distinguish the contribution rate of each influencing factor to runoff change.Finally,the influence of climate and vegetation cover change on runoff change was discussed. From 1964 to 2015,the runoff of Baihe and Shayang stations showed a decreasing trend,with the change rate of -2.797 mm/a and -1.875 mm/a,respectively.The overall precipitation of Baihe station displayed an upward trend with a change rate of 0.080 mm/a,while that of Shayang station showed a downward trend with a change rate of -0.652 mm/a.The potential evapotranspiration exhibited a decreasing trend with the change rates of -1.403 mm/a and -1.793 mm/a,respectively. The abrupt change point of the annual runoff sequence at Baihe and Shayang stations was 1991,thus the period was divided into the base period (1964-1991) and the change period (1992-2015).Compared with the base period,the decreasing rates of rainfall and potential evapotranspiration in the change period of Baihe station was 4.72% and 1.11%,respectively,and those in Shayang station was 4.45% and 3.5%,respectively.The underlying surface parameters showed an upward trend compared with the base period,with an increased rate of 4167% and 2905%,respectively.The elastic coefficients of runoff to rainfall,potential evapotranspiration and underlying surface at Baihe station in the change period was 1.79,-0.79,-064,respectively,and those in Shayang station was 2.07,-1.07,-0.71,respectively,which indicated that the runoff at both stations is most sensitive to precipitation and least sensitive to an underlying surface. The underlying surface changes were the main factor of runoff change in the Hanjiang River basin,and its contribution rate to the runoff change at Baihe and Shayang stations was 74.67% and 76.37%,respectively;The contribution rate of precipitation to the runoff change at Baihe and Shayang stations took second place,and the contribution rate was 27.80% and 37.73%,respectively.Potential evapotranspiration had a negative contribution to runoff change at both stations,and the contribution rate was the lowest. The increasing annual precipitation at Baihe station,the hydrometeorological elements in the Hanjiang River basin generally showed a decreasing trend from 1964 to 2015.The underlying surface changes were the major controlling factor of runoff reduction in the Hanjiang River basin,and the normalized difference vegetation index in the change period was increased as a whole compared with the base period.The vegetation change was an important reason for the overall decrease of runoff in the Hanjiang River basin,and the influence of climate factors was relatively small. The complementary relationship method based on Budyko′s hydro-thermal coupling equilibrium equation is simple and practical,but the physical meaning and quantitative expression of the underlying surface parameter in this equation need to be further clarified.
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