Study On Mechanism Of Ecohydrological Response At The Water Resources Shortage Watershed In Northern China

The Yongding River basin is a typical water-deficient basin in the northern China.Climate change and human activities of large scale have led to widespread water shortages and the ecosystem degradation in the Yongding River basin.The changes of land uses and land cover(LULC)because of human activities of large scale have significantly changed the runoff variation and the study on the mechanism of ecohydrological responses has become one of the most interested topics in China.In this study,the spatiotemporal patterns of meteorological,and hydrological elements,and LULC changes since 1980s were analyzed to reveal their effects on runoff changes in the Yongding River basin.The SWAT model of Yanghe River was constructed to predict the past impact of climate change and LULC on runoff changes.The spatial LULC optimization regulation scheme for Yongding River basin was constructed according to the SWAT modulation.Based on optimal configuration of vegetation replantation in the Yongding River basin,we provided a suitable method to regulate the ecohydrological process.According to the project of ' Yongding River Comprehensive Management and Ecological Restoration Overall Plan',we predict the future changes of runoff in the Yanghe River Basin under the condition of predicted climate change LULC changes.The major results are:(1)The climate change and LULC changes dominated the runoff variation of Yongding River basinThe spatial variation of air temperature and precipitation gradually changed significantly from the southeastern to northwestern of Yongding River basin,although the hot spot of air temperature formed in the Beijing metropolitain.According to the longterm air temperature records,the average temperature increased at the rates of 0.36 ?/10a,0.38 ?/10a in the upstream of Yongding River,Sanggan River and Yanghe River,respectively.During the same period,the variation of precipitation in the corresponding areas was not significant.However,the significant total amount reduction of runoff were 1.371 billion m3,796 million m3,and 530 million m3,respectively,in the corresponding watershed.The abrupt changes of temperature and runoff were significantly by using the cumulative anomaly method analysis.And there is no significant abrupt change in precipitation during the same period,however,the increasingly interannual fluctuations of precipitation indicated the global climate change.The precipitation and runoff of Yongding River and its main tributaries formed two main cycles based on the cyclical variability analysis.Before the 1980s,the annual and chronological changes of runoff were positively correlated with air temperature and precipitation.Since then,the changes of annual and chronological runoff are not positively correlated with air temperature and precipitation.One of the typical example is the increase of precipitation and the decrease of runoff in the 1990s.The total amount of runoff decreased 289 million m3(23.14%),compared with the multi-year average amount,indicating the impact of human activities increased significantly in Yongding River.The LULC changes were analyzed at the interal of ten years in compared with the background of 1980s.The cultivated land area decreased from 20290.89km2 to 18983.63km2.The forest area increased from 9592.38km2 to 10654.43km2.The grassland reduced from 1,3236.3km2 to 12,468.52km2.And the urban area increased from 1215.61 km2 to 2508.31 km2.Based on the comprehensive dynamic degree and transfer matrix analysis,we identified that the quick changes of LULC mainly happed during the period of 2000-2010.The calculation results of the eco-environmental quality index show that the ecological environment quality in the upstream region of Yongding River improved gradually due to the ecological restoration projects such as replantation.(2)Quantitative analysis of the effects of climate change and human activities on watershed runoffBased on the climate elastic coefficient method of the Budyko's hypothesis and the calculated evaporation according to the precipitation records by using the Penman-Monteith formula,the values of parameter of land surface ranged from 0.5 to 2.0 in the watersheds of Yongding River and its tributies.The results recommended that the Zhang formula should be acceptable to explain the contribution of climate change and human activities to the variation of runoff.By comparing precipitation elastic coefficients and potential evapotranspiration elastic coefficients,in the upstream of the Yongding River and the main tributaries Sanggan River and Yanghe River,the sensitivity of runoff to precipitation is greater than to potential evapotranspiration.The impact of climate change and human activities accounted for the explaination of runoff changes was 20 percent and 80 percent,respectively.(3)Changes of runoff to climate and LULC in the Yanghe River basinThe SWAT model of the Yanghe River Basin was constructed to simulate the effects of climate change and LULC changes on runoff based on land uses of 1986-1995.From 1996 to 2005,the average annual precipitation decreased 17.72mm and the temperature increased 0.65 ?.During that period,the climate change accounted for 40.41%decrease of the river runoff.At the time,the changes of LULC were minimum and accounted for 0.7%increase of the river runoff and 1.32%increase of surface water yield.And High-intensity human activities such as groundwater exploitation the river irrigation,reservoir construction are the main reasons for the decrease of surface runoff in the basin,accounting for 60.29%.During the period of 2006-2012,the average annual precipitation decreased by 48.74mm,the annual average temperature increased by 0.44?.The decrease in surface runoff decreased to 22.66%,land use change caused surface runoff to decrease by 2%,and water production increased by 1.11%,while the intensity of human activities such as river diversion,reservoir construction,and groundwater exploitation increased,result in a decrease in surface runoff in the basin,accounting for 75.34%.The runoff response studies under different land use/cover scenarios in the Yanghe River basin was carried out,and the quantitative response relationship of the basin eco-hydrological process was established.It was found that forest land,shrub forest,sparse forest land and grassland were the land use that caused the runoff attenuation of the basin.The order of reducing runoff was followed by forest land>shrub forest>sparse forest>grassland.(4)Optimal regulation of ecological hydrological processes and prediction of runoff changes in the Yanghe River BasinCombined with the topographical differentiation characteristics of land use,and based on the principle of promoting clear water production and drainage in the basin,the land use/cover space optimization and control scheme of the basin was proposed.After optimization,the runoff of the basin increased by 1.25%.The ecological and hydrological process optimization control method based on vegetation optimization configuration in the water shortage basin in northern China is formed.Analysed on the trend of land use change in the Yanghe River Basin from 1990 to 2015,based on the overall goal of the "Yongding River Comprehensive Management and Ecological Restoration Overall Plan",the construction of the river protection forest and water conservation forest in the Yanghe River basin,The land use forecast of the Yanghe River basin in 2025 was completed by the CA-Markov model constructed using IDRISI software.The results show that there will be an increasing trend of forest land,shrub forest and sparse forest land in 2015-2025,and Coupled the land use data for 2025 and the future climate data simulated in the second stage of the collective dynamic scale reduction plan in East Asia(CORDEX-EA-II),the study predicts the surface runoff of the Yanghe River basin from 2020 to 2030 using the SWAT model.Compared with the base period of 1986-1995,the results show that the annual average precipitation increased by 14.18%,and the average temperature increased.1.26 ?,and the future surface runoff will increase by 13.85%without considering the influence of other human activity factors,such as social water use and reservoir construction.