Influencing factors of surface runoff attenuation in mountainous areas of Daqing River basin
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Abstract:
Runoff attenuation has been a serious threat to the natural ecological and social production of the river basins,and it was usually attributed to climate change and human activities.The research methods were generally divided into two types,one was based on statistical data to identify the impact of climate factors and human activities factors by the difference of the relationship between precipitation and runoff in two periods.The other approach was based on the hydrological model that simulate the difference in runoff under different climate conditions and different surface conditions to distinguish the effect of climate and human activities.Due to the limitation of data acquisition,there is no mature attribution method for the contribution of vegetation,soil and water conservation projects and other factors to runoff attenuation.Therefore,Daqing River basin was taken as the study area to analyze the influence mechanisms of different factors on runoff and investigate the contribution of each factor to runoff attenuation. Runoff changes at three typical hydrological stations in the Daqing River basin were analyzed,and the abrupt change of surface runoff was analyzed using the Pettitt mutation test.The first abrupt change occurred in 1983,and the second abrupt change occurred in 1997.Thus,the runoff series from 1961 to 2016 was divided into three periods (T1,T2 and T3) based on the above mentioned two mutation points.Additionally,the evolution patterns of rainfall in flood season and non-flood season,potential evapotranspiration,mountain water conservation and reservoir construction were analyzed in the three periods,respectively.Sensitivity analysis method was applied to evaluate the contribution of each influencing factor to runoff attenuation in the Daqing River basin. The results showed that there has no significant change in the rainfall in the three periods in the Daqing River basin,but the rainfall decreases in flood season and increases in non-flood season,which is one of the important reasons for the decrease of runoff.In the mountainous area of the Daqing River basin,the heavy rainfall showed a decreasing trend,while the medium and small rainfall showed an increasing trend.The rainfall intensity in the mountainous area of the Daqing River basin gradually decreases,which leads to the decrease of storm runoff.The potential evaporation in the Daqing River basin decreases and then increases during the annual,flood and nonflood seasons.The increase of evapotranspiration capacity in the flood season during the T3 period means the increase of regional actual evapotranspiration and the corresponding decrease of runoff from precipitation decline.The annual maximum NDVI in Daqing Mountain has shown an increasing trend since the 1980 s,with an average annual growth rate of 0.002 3.Vegetation conditions have become better and more precipitation was retained by the canopy and evaporated into the atmosphere,thus reducing the runoff formed by precipitation.The reservoirs led to an increase in evaporation,with evaporation loss of 37.96 million m3 and 36.59 million m3 from the reservoirs in the T2 and T3 periods,respectively. In conclusion,the influence of precipitation on surface runoff in mountainous area of the Daqing River basin is mainly reflected in the flood season.The decrease of precipitation and the weakening of rain intensity in the flood season reduced runoff,while the increase of evaporation capacity leads to the increase of actual evaporation loss in the flood season,which further aggravatesthe attenuation of runoff.The increased interception of vegetation canopy and the enhancement of soil water storage capacity caused by the water conservation project were important reasons for the attenuation of surface runoff in the T2 and T3 periods.The change of precipitation in flood season in the T1 period is the main reason for affecting runoff.The large increase of terrace area in the T2 period is the main reason for the decrease of surface runoff.In the T3 period,precipitation decreased in flood season and the increase of the proportion of evaporation to precipitation due to the improvement of vegetation quality lead to the decrease of runoff.
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