Dynamic Response Of Eco-hydrological Process To Human Activities And Climate Change In Chaobai River Basin

Water problems and water crisis are of widespread concern around the world under the background of climate change and intense human activities. As the only source of drinking water in Beijing which is confronted with severe water shortage, the role of Chaobai River Basin is extraordinarily significant in Beijing. In the present study, the five watersheds of Tumen, Banchengzi, Hongmenchuan, Huaihe and the upper Chaobai River were chosen as research areas. The changes of land uses and hydro-meteorological factors during the research period were analyzed based on long time series of land use and hydro-meteorological data, furthermore, the inflection years were revealed through non-parameter test; then land use, temperature and precipitation were predicted by use of CA-MARCAV and future climate scenarios respectively; subsequently the reasons for runoff, sediment and water quality changes were assessed through using AWY model, hydrological analysis method and binary cycle theory. Besides SWAT model was used in the study to simulate and forecast the impacts of reservoir establishment, forest vegetation, land use and climate change on runoff, sediment and water quality, and quantifying each contribution to each hydrological factor. The main results were as follows:(1) Land use changes in Tumen watershed mainly occurred in the edge junction of forestry, and it was found that it produced few changes between different periods; Agricultural land in Banchengzi watershed transformed frequently during the research period, the areas of broad-leaved forest and water body presented the uptrend an downtrend respectively; land uses in Hongmenchuan watershed did not change largely, and had a state of wavelike form among different terms of land uses; Land uses have taken place lots of changes in Huaihe watershed, and it was further observed that speeds of land uses changes became larger as time went; as regards the upper Chaobai River Basin, it did not produce large changes. Land uses in Chaobai River Basin were forecasted in the future, the results showed that forest, cultivated land and unused land would reduce in 2020 and 2030, while water body, grassland and built up increase obviously compared with the present situation. It was analyzed that Household contract responsibility system and Beijing and Tianjin sandstorm source control project may be the main driving force of land use change in Chaobai River Basin.(2) Annual precipitation and potential evapotranspiration in 1956-2009 did not change significantly in Chaobai River Basin, while air temperature climbed evidently, and an inflection point (in 1990) was identified through visual observation. With regard to annual runoff and sediment yield, they both took on a rapid decline during the research, and the change point was in 1978. The variation coefficients of water quality indicators in Bai River Basin (Daguanqiao station)were greater than that in Chao River Basin (Xinzhuangqiao station) except chloride, dissolved oxygen, permanganate index, nitrate nitrogen and the atomic. It was predicted that annual average surface temperature would increased 1.2℃and 1.65℃in 2020 and 2030 respectively compared with the period of 1961-1990. Meanwhile, average rainfall increased 0.21mm and 0.05mm respectively in summer.(3) In Chaobai River Basin, forest land markedly influenced on monthly runoff by sensitivity analysis, then was farmland, grassland and built up, and water body and unused land was not observed to have clear impact on runoff. In 1980-1989, the contribution rate of land use to runoff change reached 40.7% in Chao River Basin and 6.5% in White River Basin. Moreover, human activities contributed 78.5% and 71.9% to sediment yield change in 1974-1997 and 1998-2007 respectively in Chaobai River Basin. Non-point source pollution accounted for 74%,91% and 73% of total COD, TN and TP output. The output of domestic waste is much larger than that of industrial waste in point source pollution.(4) Channel and Dam projects in Chao River Basin and White River Basin played a key role in reducing runoff in the 1980s, and it contributed 95% and 83% to runoff reduction in the two watershed respectively; however, it did not bring great impact on sediment transport, and the contribution rates were 41% and 40% respectively. Take Channel and Dam projects as research background, SWAT model was used to calculate the effect of land use on runoff change in the two watersheds, the results indicated that the contributions were 42% in Chao River Basin and 24% in White River Basin, correspondingly 40% and 49% to sediment change in the two watersheds. In order to understand the effect of forest on runoff, "clear cutting" method was adopted in Chaobai River Basin and its nest watersheds, and it was found that different forest cover influenced about 60%-70% of runoff reduction.(5) Based on the forecast results of land uses and climatic factors, SWAT model was calibrated and validated in the watershed. The period of 1991-2000 was taken as basal period, and 2001-2010, 2011-2020 and 2021-2030 as evaluation period; It was simulated that the contributions of land uses to runoff changes were 23%,43% and 25% in the three evaluation stages respectively in Chao River Basin, while correspondingly 35%,36% and 23% in Bai River basin; the rest of runoff change may be caused by climate change. It can be concluded that human activities may intensively affect runoff process in 2011-2020.In conclusion, the present study provides some support on the sustainable water resources management and land use optimization through researching the Land-cover/climate changes and their impacts on hydrological processes.