| Urban land use expansion caused strong changes of land usage and ground cover accompanied with rapid development of soical economy.Important changes of land use take place in different spacial and temporal scale as a function of natural evolution and human activity.Those changes of underlying surface compose an artificial‘systemic disturbance'which exert important impact on hydrological process of river basin.This impact does not only reflects changes of surface water and heat condition but also influences spatial and temporal distribution of hydrological process.Furthermore,it may compose effect on catchment rainoff-runoff mechanism which will normally cause redistribution of catchment runoff at different scale resulting broken habitats,drastically reduced biodiversity and mutated biological phenology,and eventually change structure and composition of regional ecological system and pose an threat on ecological security.Researching changes of hydrological process resulted from natural environment changes and human activities can be an efficient pathway for water resources management and ultilization.Regonize those spati-temporal changes of hydrogical components caused by changes of land use is meaningful for optimizing land usage structure and water resource planning.This research analyzes changes of runoff and water conservation capacity through using IHA/RVA method to quantitatively assess eco-hydrological variability of river and its potential ecological effects based on measured runoff data from Waizhou Station over Ganjiang River Basin from 1960 to 2017.Meanwhile SWAT model was built by combining land use data from 1980,2000,and 2015,meteorological data from1960-2017,and measured runoff data from 5 hydrological stations of basin.Effects of spatio-temporal differentiation of hydrology processes such as infiltration,evaporation,runoff discharge and changes water conservation capacity.Then quantitative analysis effects of climate and land use on comprehensive effect on hydrological process-runoff changes using correlation analysis and quantitative differentiate method.Main conclusions are as follows:(1)Based on measured runoff data from control station of the lower reaches of Ganjiang River to Waizhou Station from year 1960 to 2017,runoff of Ganjiang River shows an ascent trend with nnual runoff increases with rate of 0.27×10~8m~3/a since 2000.Furthermore,runoff coefficient,river baseflow coefficient,runoff stability and water conservation capacity has increased.Conversely,variables such as elasticity coefficient,variability coefficient has decreased.This is closely related to implementation of ecological forest protection projects,conversion of farmland to forests and lakes and construction of water conservancy facilities over Ganjiang River Basin.Overall hydrological change of runoff is 32.27%,which constitutes a mild change.High/low discharge indicators show an higher degree of change from ecological hydrology index system which means high flow decreases and low flow increases.Runoff enjoys an slight change among one year an peak adjustment of water conservancy facilities is significant.(2)The area of cultivated land and forest land of Ganjiang River basin continued to decline from 1980 to 2015.The proportion of grassland has remained at about 5%for many years.The area where land use types have changed is scatterly distributed.The distribution of land use change in some areas of lower reaches of Ganjiang River from2000 to 2015 performance a certain degree of concentration trend.There are both spatial and temporal differences in land use change of river basin.From 1980 to 2000,conversion between forest land,arable land and grassland was the main conversion area,which accounts for 1.35%of total area of river basin,and dynamic change degree of comprehensive land use was 4.79%.From 2000 to 2015,it was mainly the decrease of forest land and increase of urban land.The conversion area accounts for 1.48%of total area of river basin,and comprehensive land use dynamic change degree was1.05%.From 1980 to 2015,area of land use conversion of watershed accounts for a small proportion of total area of watershed,and the rate of conversion shows a downward trend,indicating that people's awareness of environmental protection,thus its impact on the natural environment has weakened.(3)There are obvious differences in runoff,evaporation and infiltration of different land use types.Simulation shows that average annual runoff of each land use type is between 0?614.53mm,average annual evaporation is between 441.21?1097.74mm,and average infiltration per year is between 0?77.77mm.From 1980 to 2015,decrease in output was mainly due to the transfer of forest land and waters,and increase in output was mainly due to the increase in urban and rural construction land and grassland.From2000 to 2015,evaporation of five sub-watersheds shows a decreasing trend.During this period,a large increase in urban and rural construction land was main reason for reduction of watershed evaporation.Increase in infiltration of thw lower reaches of Ganjiang River from 1980 to 2000 was due to the implementation of the policy of returning farmland to grassland,which increased the water conservation capacity of river basin.The decrease in infiltration from 2000-2015 was mainly due to the rapid increase of urban and rural construction land of river basin.Nevertheless,due to mutual conversion between land-use types and superposition of their impacts,integrated hydrological effect on basin scale has been greatly reduced,and land-use changes in different periods have caused little difference in watershed runoff,evaporation,and infiltration.From 1980 to 2015,average runoff of entire Ganjiang River Basin has increased amount to 2.33×10~8m~3 due to land use changes.Because area converted by land use accounts for a small proportion of total area of the basin,impacts of pure land use change on the runoff of Ganjiang River into the lake is very limited.Under three-period land use situation,runoff coefficient of increased,elasticity coefficient and variability coefficient decreased,which coincided with the change of the measured runoff.The water conservation capacity of Ganjiang River is steadily improving.(4)The humidity,wind speed,and radiation of Ganjiang River Basin shows a downward trend since 2000,while precipitation and temperature have performance an increasing trend.Humidity and precipitation are positively correlated with runoff,evaporation,infiltration,and discharge;wind speed and radiation are negatively correlated with runoff,infiltration,and discharge;air temperature is positively correlated with discharge;there is a positive correlation between radiation and evaporation,runoff.The runoff,infiltration,and runoff of the Ganjiang River Basin are mainly affected by precipitation,while evaporation is mainly affected by radiation.There is no obvious correlation between the impacts of land use change area on the hydrological process,but the conversion between land use types has an important impact on local hydrological process.Runoff depth of Ganjiang River Basin changes and the contribution rates of climate and land use are 91.01%and 8.99%,the increase of Ganjiang River runoff is mainly affected by climate change. |
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