| Urbanization is an important feature of today's world development.It is a stage that no country or region can surpass,but it also brings corresponding ecological and climate problems.In the process of urbanization,the original vegetation and soil are gradually covered by impervious or weakly permeable ground,and the city will easily form groundwater in heavy rain.At the same time,population aggregation has changed the thermal and dynamic nature of the underlying surface of the city,affecting the climate such as temperature and rainfall in the region,causing the island to produce a heat island effect and a rain island effect.Under this background,increasing green space vegetation can effectively accelerate the infiltration of rainwater and improve the water storage function of green land,thereby reducing the risk of flood disasters in cities and improving the ecological level of cities.In order to reveal the variation characteristics of regional soil water and its availability under urban background,regional grasslands of the Irrigation,Drainage and Hydrology Ecological Experimental Field in Yangzijin Campus of Yangzhou University(P1),and the grassland in Jiangyang Road South Campus of Yangzhou University(P2)were chosen as the study area.Based on the measured data of hydrology and meteorology,ET0 over the reference crop and ET over the grassland were estimated by using Penman-Monteith equation and a revised Penman-Monteith equation which was recommended by FAO,respectively,and moisture availability was evaluated.At the same time,the correlation between meteorological factors and ET and ma is analyzed.A model for one dimensional calculation of soil water content has been developed based on Richards' equation combined with finite difference method.Model applicability was validated via simulation of the observed soil water content in the soil layer of 0?10cm below the ground surface.The Root Mean Square Error(RMSE)and Nash-Sutcliffe efficiency(NSE)are used to test the practicability and efficiency of the model.The results indicated that:(1)In the calculation period(2017.01.01-2017.12.31),ET0 on P1 and P2 are 1134.0 mm,which was slightly higher than the rainfall(989.7mm)in the same period;ET on P1 and P2 were 129.7 and 122.2 mm,which accounted 24.2 and 22.9%of rainfall in the period of 2017.07.01-2017.09.30.In the calculation period(2018.01.01-2017.09.30),ET0 on P1 are 950.3 mm,which was slightly less than the rainfall(1036.5mm)in the same period;ET on P1 were 230.9mm,which accounted 27.4%of rainfall in the period of 2018.05.01-2018.09.30.(2)In the calculation period(2017.07.01-2017.09.30),moisture availability coefficient(ma)were 0.39 and 0.37 of the P1 and P2,respectively.In the calculation period(2018.05.01-2018.09.30),ma were 0.37 of the PI.(3)The correlation degree between ET and various meteorological factors is as follows:solar radiation quantity>wind speed>relative humidity>temperature.The degree of correlation between ma and various meteorological factors is:wind speed>relative humidity>temperature>solar radiation.(4)The Root Mean Square Error(RMSE)are 0.012 and 0.021 and the Nash-Sutcliffe efficiency(NSE)are 0.830 and 0.928 of the numerical model of P1 and P2 in the calculation period(2017.07.01-2017.09.30),the RMSE are 0.014 and the NSE are 0.817 of the numerical model of P1 in the calculation period(2018.05.01-2018.09.30),which indicates that the less error exists between the model results and the observed data of the soil water content,and model has a relatively high accuracy for one-dimensional soil water calculation.The results are expected to provide partial basis for the further researches on hydrological cycle of grassland and the advances of sponge city via enlarging the green vegetation under the background of urbanization. |
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