Research On The Assessment And Evolution Of Green Water Resources Based On Hydrological Cycle Simulation

The Chaobai river basin is the catchment basin of Miyun reservoir,which is an important water source of Beijing.The surface runoff in Chaibai river basin rapid decrease in recent years,the water shortages problem not ony seriously restricted the local economic and social development,but also threatened the water security in Beijing.Based on the regional hydrologic cycle simulation,the space-time distribution of green water resources in Chaobai river basin was evaluated.Furthermore,the change process and influence factors of green water resources have been further analyzed.The main results are as follows:(1)Compare to the existing evaluation methods of green water resources,several new indicators including the efficient used green water and utilizable green water were proposed to evaluate the green water resources in Chaobai river basin,which perfected the evaluation system of green water resources.(2)By using the linear tendency estimation method,moving average method,and Mann-Kendall method,the change trend of precipitation and surface runoff in the study area has been analyzed.The results shown that the annual precipitation in Chaobai river basin decreased in the study period and the decreasing tendency were not significant.However,the surface runoff in the basin has dropped significantly.The land use change in study area is mainly reflected in the reducing of woodland after the first increase and the increasing of farmland and grassland after the first decreases.(3)The SWAT model in Chaobai river basin was established,the model calibration and validation have also been finished.For the Zhangjiafen and Xiahui gauge stations,the deterministic coefficient(R~2)and Nash coefficient(NS)are above 0.8 during model calibration and the values of these two coefficients are above 0.7 during model validation.The results of model calibration and validation proved that SWAT model performed well in simulations,it is feasible to evaluate the green water resources in HRB with the model results.(4)The time-space distribution of the green water resources in Chaobai river basin has been evaluated.The annual mean green water resources in Chaobai river basin is501.21 mm,among it,the efficient used green water is 412.08 mm and the utilizable green water is 89.13 mm.Farmlands have the highest convertion efficiency of precipitation,89.64%of the precipitation which landing on farmlands as transformed into the green water.(5)By using several change trend analysis methods such as the Mann Kendall method,the change trend of the green water resources in Chaobai river basin has been analysed.Besides,the Hurst index was used to predict the change tendency in the near future.The results show that the efficient used green water in the Chaobai river basin rising in the study period but not significant,besides,the change tendency in the future instead of now.The quantity of utilizable green water in the study area increased significantly from 1970 to 1980.However,there was a mutation in 1999 and the utilizable green water began to decline.The decreasing tendency became significantly2002 and the change trend is consistent in the near future.(6)By setting the different scenarios(combined of meteorological and land use data in different periods),the impact of climate change and land use change on the green water resources in Chaobai river basin have been quantitative analysed.Compare to the baseline period(1989~1998),the quantity of the efficient used green water in evaluation period(1999~2008)decreased by 4.12 mm,the contribution rate of climate change and land use change are 125.41%and 25.41%,respectively.The quantity of utilizable green water in evaluation period decreased by 50.65 mm compared to the baseline period,the contribution rate of climate change and land use change were101.98%and 1.98%,respectively.Overall,climate change is the main influencing factors of green water resources change in the study area.