The Response Of The Hydrology And Water Quality At Watershed Scale Under The Climate Change And Land Use/cover And Dynamics

Land use/land cover(LULC)changes and climate changes are important factors that greatly affect the hydrology and water quality of a watershed.Multi-purpose water resources manage-ment and land use planning also need to take these changes into the consideration.Accurate prediction of the impact of LULC change and climate change on water environment is essential for developing the harmonious human society and natural ecosystem.With the sensitivity to vari?ous external disturbances,hydrology and water quality are the principal environmental indicators.LULC changes and climate changes,such as precipitation,temperature,wind speed and other meteorological indicators,affect the regional hydrology,water quality characteristics,as well as other natural and social environmental factors.The objectives of this study are to evaluate the impact of LULC changes and climate changes on hydrology and water quality at watershed scale,to explore the cause of water resources response under LULC change and climate change scenarios,to predict quantitatively future LULC changes and climate changes,and then,model the changes of watershed hydrology and water quality.By using Geographic object-oriented image analysis technique(GEOBIA),LULC change prediction model(Cellular automata Markov model,CA-Markov),watershed hydrology and Water quality model(Soil and Water Assessment Tool,SWAT)and the Coupled model intercomparison project(CMIP5),this dissertation established a system of quantitative evaluation and prediction of hydrol-ogy and water quality,and applied this system to assess and forecast water environment in Tiaoxi watershed,Zhejiang Province(Southeastern China).Quantitative analysis of LULC changes and climate change between 1985 and 2015 was conducted.We simulated and re-constructed the dynamic process of watershed hydrology and water quality and forecasted the future evolution of LULC changes and watershed hydrology(evaporation,flow),water quality(sediment,total nitrogen,total phosphorus)changes.Results show,due to the urbanization process(taking a large number of cultivated land and orchard)and agriculture upgrading(turning a large number of crop land,forest land into orchard),LULC change drastically in Tiaoxi watershed,with building lands(+332%),orchard(+611%)ex-panded rapidly,cultivated land(-73%)and forest area(-11%)declined substantially.In terms of climate change,the temperature increased significantly(+0.77 ?/10 a),and rainfall pat-terns shifted significantly.Though the amount of averaged annual rainfall showed insignificant changes,the number of raining days decreased(8.76 days/10 a),the events of extreme rainfall presented a trend of increase.The rainfall under regular season increased(+ 59.6 mm/10a)sig-nificantly,but with a significant reduction of rainfall in dry season(61.1 mm/10a).Meanwhile,LULC changes led to the changes of underlying surface properties.Consequently,changes of meteorological and hydrological parameters at local watershed occurred.The runoff coefficient at upstream decreases,while the runoff coefficient at downstream increases.The occurrence of runoff extremum increases.By using SWAT model,the influences of LULC changes and climate changes on surface hydrology and water quality were regenerated.Results show that the SWAT model suits well in Tiaoxi watershed The simulated evaporation,runoff,sediment,total nitrogen fit well with mea-sured values.For the past thirty years,the changes of LULC by human activities has considerable influence on surface runoff(+25%),lateral flow(-23%),water that percolation to the shallow aquifer(-24%),sediment yield(+26%)and nitrate that transported by the surface runoff(+52%).By integrating the LULC scenarios simulated by CA-Markov model and the climate patterns generated by CMIP5,we quantitatively predicted the impact of climate and LULC changes on hydrology and water quality to the end of the century.Results showed that,due to the climate change,evaporation(+12%?+18%),surface runoff extremum(+6%?+36%),sediment load(+13%?+43%)will be significantly changed;Future LULC changes will exert great impact on surface runoff(+14%?+34%),sediment load(+6%?+22%)and total nitrogen in surface runoff(+20%?+42%).This dissertation developed a system approach for quantitative evaluation and prediction of hydrology and water quality.Also,a multi-LULC approach was used to improve the SWAT model to make it suitable for long-term simulation in the area where LULC changes drastically,result-ing in extending the application fields and improving simulation precision of the model.This paper uses the approaches of modeling and simulations that quantitatively handled with challeng-ing environmental issues,revealed the harmonious relationships between man and nature and also alerted that possible ecological consequences should be avoided.Ultimately,this study can help management agencies make decisions or policies about daily living,production,and environmen-tal protection in more scientific and reasonable ways at watershed scale.Nature and human society are complicated,therefore,the variables involved in this paper must not cover all of them.But the precision of model will be further improved with the development of computer technology and human cognition of geochemical and geophysical theory.