| Evapotranspiration is the important link, which is connected to the water, energy and carbon balance loop. By influencing the surface evapotranspiration, climate change and land use change caused by the urbanization have a direct impact on the water balance and energy balance in the watered scale. As a result, when quantitatively evaluating the hydrological and meteorological effects of urbanization, the change mechanism of the land use/cover and evapotranspiration must be considered. This is the basis to correctly understand a series of environmental consequences brought by the urbanization, and is of great significance to realize the sustainable development by reasonably evaluating the ecosystem service function of river basin and improving the level of watershed management.The paper takes the Qinhuai river basin that has the fast urbanization as the study area. Applying the linear analysis and the M-K inspection methods to analyze the climate characteristics of the basin in 2000-2013; Using remote sensing image to extract land use/cover map of the river basin in different periods and detect its characteristics; Calculating and estimating the potential evapotranspiration and the actual evapotranspiration of the basin in 2000-2013 respectively based on Penman-Monteith formula and remote sensing data, and analyzing their change trends; Simulating the actual evapotranspiration of the basin based on the construction of the SWAT model in the Qinhuai river basin, and calibrating and verifying the model with the combination of the actual evapotranspiration that the remote sensing estimated in order to improve the accuracy and applicability of the model. On this basis, driving the model by the construction of different climate change and land use change scenarios to simulate and analyze the change trend of the actual evapotranspiration in watershed scales under the different scenarios.The main conclusions are as follows:(1) The annual and rice growing season’s temperature and precipitation don’t change significantly in recent 14 years. From 2000 to 2013, the annual temperature and precipitation of Qinhuai river basin is decreasing, temperature trend rate is 0.01 ℃/a, precipitation trend rate is 2.86 mm/a; Temperature and precipitation in rice growing season(June-September) are on the rise, temperature trend rate is 0.03 ℃/a, precipitation trend rate is 8.61 mm/a.(2) The change of the land use/cover in the basin is obvious in recent 14 years, which is the urban area greatly increased but the paddy field dramatically decreased. The land use/cover of the Qinhuai river basin has certainly changed in recent yeas. The land use type of the Qinhuai river basin is given priority to with paddy field, dry land and forest land in 2000. The paddy field area is the largest, accounting for 45.38% of the total area; followed by dry land area, accounted for 28.13%; urban surface and water area is lesser, the proportion of 8.53% and 3.96% respectively. The land use type of the basin is given priority to with paddy field, dry land, and urban surface in 2012. The paddy field area is greatly reduced, decreased by 9.72%, but urban surface has a rapid growth, which is close to the dry land area accounting for 23.36% of the total area.The forest land and water area is smaller, and the proportion is 10.82% and 3.68% respectively.(3) The potential evapotranspiration (PET) of the basin shows a trend of increase, but the actual evapotranspiration (ET) has a trend of decrease. The interannual variability of the PET in Qinhuai river basin is on the rise in general from 2000 to 2013, and its tendency is 6.19mm/a. The change of the PET in one year presents an obviously unimodal characteristics, and its peak almost appears from July to August in each year, about 150-160mm. In contrast to potential evapotranspiration, the actual evaporation of the basin is on the decline from 2000 to 2013, the decline rate is 3.58mm/a. The ET of the basin presents an obviously unimodal characteristics which peak mostly appears from July to August of each year, about 100-120mm.(4) Using the SWAT model to simulate the ET of the basin, and its effect is better. By constructing the SWAT model of the Qinhuai river basin to simulate the ET of the basin in 2000-2013, and make sensitivity analysis of the model’s key parameters. By using the amount of actual evapotranspiration estimated through remote sensing to rate the parameters and its changes values that make the yearly and monthly simulation result best. Simulation results show that the sensitivity of the base flow back index (ALPHA_BF), the biological efficiency of the hybrid (BIOMIX) and the potential maximum leaf area index (BLAI) is stronger. The Nash coefficient (Ens), determination coefficient (R2) and the relative error (Re) are 0.57,0.64,0.14 separately in the calibration period (2002-2007); they are 0.59,0.68,0.14 respectively in validation period (2008-2013).(5) Both climate change and the paddy field area lead to the decrease of the ET, but the change of the ET is mainly related to the drastically reduce of the paddy field area. Based on the checked SWAT model, the monthly ET on river basin scale under different climate change and land use/cover change scenario is simulated. The results show that with So scenario (rainfall and temperature is constant, and the land use situation is in 2000 and 2012) as a benchmark, the ET of the other scenario show a trend of decrease. In the situation of the precipition and temperature unchanged, and the land use in 2012(S1), the ET has a drop of 3.76%; in the situation of the precipitation and temperature unchanged, but the paddy field changes into urban area(S3), the ET has a largest decline, about 23.25%; the same situation in other conditions, the ET caused by the paddy field decreases much more obviously rather than it caused by the dry land(S2 and S3); the climate change has an obvious impact on the ET, if the precipitation and temperature increase, the ET changes(S3, S4 and S5). |
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