| Under the current environment,the hydrological cycle was influenced by both climate and human activities.Due to the complexity of the human activities,their contributions to the changes of hydrological cycle had increased significantly.In order to deeply understand the main driving forces of the hydrological cycle under the changing environment and solve the imbalance between the supply and demand of water resources in the basin,it is urgent to explore the impacts of climate change and the human activities on the variations of hydrological cycle in the basin.In addition,the changes of hydrological cycle directly affected the spatial and temporal distribution of water resources,leading to the gradually prominent problems of meteorological and hydrological drought in the basin.Especially in recent years,the impact of global warming had intensified,and the increase of high temperature and heatwaves in crop growing season had further induced the frequent occurrence of flash droughts in the river basin.Drought had seriously affected the sustainable development of ecology,agriculture and social economy.Therefore,this article selected Weihe River Basin as the research object,resulting from that this basin was obviously affected by global warming and the human activities.Based on the geography,climate and hydrology theories,using distributed hydrological model and global climate model data,the influences of meteorological elements,land use,and the direct human activities on the hydrological cycle changes were quantitatively analyzed;The temporal and spatial variation characteristics of flash drought,meteorological and hydrological droughts in Weihe River Basin during the historical period were studied;Four optimal climate model data were selected to predict the spatial and temporal variation trends of hydrological cycle and droughts in the future,so as to provide the theoretical references for solving the contradiction between supply and demand of water resources in this basin and preventing and resisting droughts scientifically.The main contents and results of this article are as follows:(1)DEM data,soil data,land use data,and the daily data from 28 meteorological stations in the basin were used to construct the distributed hydrological model SWAT in Weihe River Basin.The model was calibrated and validated by using the measured streamflow data from Linjiacun,Xianyang and Huaxian hydrological stations.In the end,the NSE of simulated and measured streamflow at the three hydrological stations were all greater than 0.5,the R2 were all greater than 0.6,and the Pbias were all between ±25%,indicating that the model was suitable for the study of hydrological cycle changes in Weihe River Basin.(2)The SWAT model was driven by 21 downscaled CMIP5 climate model data(NEX-GDDP data set)to analyze the temporal and spatial expression of the streamflow output in the Weihe River Basin.The study found that CMIP5-SWAT had a good spatial distribution of streamflow,and the correlation with the actual streamflow distribution was 0.95-0.99.The average value of multi-year streamflow was well simulated,but the trend of time was weak.In this paper,through the comprehensive evaluation of 21 models,four models with the best comprehensive evaluation capability were selected,namely GFDL-CM3,MIROC5,MPI-ESM-MR and NorESM1-M.(3)Based on the SWAT model,six scenarios were designed to quantitatively analyze the effects of meteorological factors,land use changes and the direct human activities on the changes of hydrological cycle factors(streamflow,evapotranspiration and soil moisture)in the Weihe River Basin.It was found that precipitation was the main factor affecting evapotranspiration and soil moisture,while the direct human activities were the main influencing factor causing significant decline in streamflow(the contribution rate is more than 50%),while land use changes had less influence on hydrological cycle in the basin.It was worth noting that the impact of temperature on the hydrological cycle in the basin was rapidly increasing in 2000s.(4)According to the different driving forces,the flash drought can be divided into heatwave flash drought and precipitation deficit flash drought.From 1962 to 2015,heatwave flash drought in Weihe River Basin was more likely to occur in the northeast,while precipitation deficit flash drought occurred more in the south of the basin.With the changes of time,the heatwave flash drought increased obviously,while the precipitation deficit flash drought decreased.This phenomenon was mainly caused by the increase of temperature,and the slight decrease of precipitation year by year in the basin.In general,the occurrence frequency and duration of precipitation deficit flash drought are both higher than that of heat wave flash drought in Weihe River Basin.(5)From 1962 to 2015,both meteorological and hydrological droughts in Weihe River Basin showed an increasing trend,and the occurrence frequency of light drought was the most.In the south of basin,meteorological and hydrological drought occurred frequently,while in the west,mild drought occurred frequently.The frequency and intensity of hydrological drought in the population aggregation area which is the southeast of the basin increased obviously.There was a significant correlation between meteorological and hydrological drought,and the occurrence of hydrological drought lagged behind the meteorological drought by 2 months.(6)In the future,precipitation in the Weihe River Basin will increase.Under its influence,streamflow,evapotranspiration and soil moisture will all increase.At warming 2?,these hydrologic elements are less stable,while the increase rate at warming 3? is higher than that at 2?.When the temperature rises by 2?-3?,the frequency of heatwave flash drought in the northeast of the basin will increase,while precipitation deficit flash drought in the southeast of the basin will rise.The precipitation in the northwest area of the basin will increase in the future,but the uneven distribution of precipitation in the year will lead to more meteorological droughts.The frequency of hydrological drought in the central and western part of the basin increased significantly compared with that in the base period. |
PDF Full Text Request