Investigating The Impacts Of Human Activities On Hydrological Drought

Due to the impact of environmental change,drought events occur frequently in China,and water resources management is facing unprecedented challenges.Human activities is one of the important driving factors of environmental change.Under the influence of human activities,the global water cycle system and regional hydrological mechanism may change,and then affect the development and evolution of drought in river basins.In this study,we selected the Nenjiang River Basin,where water use conflicts are prominent and droughts occur frequently,as the research area,to investigate the changes of runoff and hydrological drought in Nenjiang River basin before and after the completion of Nierji reservoir,and to quantify the impacts of human activities on runoff and hydrological drought.The results are as follows:(1)Analysis of runoff change in the basin.Compared with the baseline period(1980-2000)without reservoir construction,the average annual discharge in 2007-2013 showed a state of attenuation(about 18%-34%).The Budyko hypothesis and the SWAT model quantified that the contribution rates of climate change and human activities to hydrological drought at shihuiyao,Tongmeng,Jiangqiao and Dalai stations were 8%-19%and 81%-91%respectively.(2)Analysis of hydrological drought characteristics in the basin.Based on the analysis of the calculation results of standardized runoff index(SRI)at different time scales,it was found that the hydrological droughts in the basin are mostly continuous droughts in spring and summer and in autumn and winter.The frequency of drought in the upper reaches of the reservoir was higher than that in the lower reaches.In the 21st century,the frequency of hydrological drought events in most areas of the basin was lower than that in the 1980s and 1990s,but the degree was more serious,and the persistent drought disasters were the most destructive.(3)Analysis of the impact of human activities on hydrological drought.Compared with the baseline period,the hydrological drought in the change period lasted longer and had greater intensity but lower frequency.Human activities were the main factor leading to changes in hydrological drought characteristics in the lower reaches of the reservoir,but they had different impacts in different durations.For long-term droughts(duration>12 months),both the duration and intensity increased,while the monthly average intensity decreased.For short-term droughts(duration<12 months),the duration,intensity and frequency were all reduced.The construction of Nierji Reservoir can alleviate floods and hydrological droughts,especially short-term droughts.(4)Analysis of hydrological drought characteristics under future climate scenarios.Five CMIP6 global climate models(GCMs)were used to predict the possible change trends and main drought characteristics of hydrological and meteorological elements and annual scale hydrological drought in Nenjiang River Basin under three shared social path scenarios(ssp126,ssp370 and ssp585)in the future(2030-2100).The results showed that the average annual temperature,precipitation and runoff of Nenjiang River Basin increased with the increase of radiation emission scenario.The future trend of dry wet alternation appeared in the basin.The four hydrological stations were mainly light drought and moderate drought.As for the whole basin,the frequency of hydrological drought would gradually decrease.