Assessing The Impacts Of Climate Change And Human Activities On Runoff At Seasonal Time Scale

It is known that runoff has changed greatly under the combined effects of climate change and human activities.Many researches have quantified the effects of climate change and human activities on runoff at the annual or inter-annual scale,ignoring the impacts on the process of intra runoff.Quantifying the effects of climate change and human activities on the intra runoff provides fundamental basis for water cycle research under changing environment,and is of great significance for rational development and optimal allocation of river basin water resources.Thus,a seasonal decomposition method based on the extented Budyko framework is proposed to quantify climate change and human activities impact on intra runoff,for Subbasin II in Fengman,and compared the results of abcd hydrological simulation method.Future changes of precipitation and temperature are evaluated under A2,A1 B and B1 scenarios using LARS-WG downscaling method,while future change of runoff is evaluated using abcd model.The contents of the article and the results of the study are as follows.The non-parametric method Mann-Kendall,linear regression and 5 years glide average methods are used to analyze the trends,double mass analysis and accumulated standard simulation errors based on the abcd model methods are used to confirm the break point.The results show that the precipitation and potential evaporation presents downward trends and runoff presents significant decreasing tendency under the common effects of the climate change and human activities,and runoff changed in 1975,which year split study period into prechange period(1953-1974)and postchange period(1975-2005).On the issues of the influence of climate change and human activities on intra runoff,firstly,the seasonal aridity index and the types of human activities are used to divide a year into three seasons: irrigation season,wet season and dry season.Secondly,a seasonal decomposition method based on the extended Budyko framework is proposed and applied to the research basin.The results show that the integrated effect of climate change and human activities leads to decreasing runoff,but each has different impact forms and magnitudes.Human activities cause decreasing runoff in all seasons,while climate change cause decreasing runoff in wet and dry seasons,and increasing runoff in irrigation season.Using hydrological simulation method based on abcd monthly water balance model and combine seasonal decomposition method,compare and analyze the results of postchange period and each periods which postchange period is divided by 10 years,and verify quantified consequences by seasonal decomposition method is reasonable;quantitative research on the wet season months(July,August,September)is investigated since there are quite a number of reservoirs(ponds)in the subbasin II in Fengman,the contribution of water storage projects to runoff variation in wet season is discussed.Future changes of precipitation and temperature are evaluated under A2,A1 B and B1 scenarios using LARS-WG downscaling method,and future runoff is obtained by the abcd model considering the effects with and without human activities.