Evolution Of The Water Cycle And Its Response To Predicted Climate Change In The Chaohe Watershed

Record greenhouse gas concentrations lock in the inevitable global warming trend.The continuous warming has changed the status quo of the global water cycle,and redistributed precipitation.At the same time,climate change has also induced extreme events such as heat waves,droughts,and floods to become more frequent.Therefore,under the more changeable climate conditions,accurately predicting the future climate change,parsing the impacts on the watershed hydrological processes,and revealing its internal mechanism,will provide critical information for the water-scarce regions to cope with global climate change,accurately predict extreme events,and optime water resources management.This paper selected the important water source of the capital-Chaohe watershed upstream of Miyun Reservoir to verify and reveal the hydrothermal coupling relationship and its control mechanism based on the long-term hydro-meteorological time-series data（1961-2020）.Then,the study predicted and parsed the hydrological response to future climate changes,applied the global climate model coupled with the hydrological model（2020-2100）.Finally,based on the Clausius-Clapeyron thermodynamical theory,the study quantified the scale and structure of the response of precipitation and surface runoff to climate warming under climate change,and clarified the changed mechanisms.The results show that:（1）The Fu-Budyko hypothesis,which covered the underlying surface characteristic parameters,could accurately characterize the hydrothermal coupling relationship in the Chaohe watershed.Optimized the parameterωand explored its impacts factors found that the vegetation conditions improved and the bare area reduced inducing the increase of parameterω.At the same time,based on the Budyko elastic coefficient analysis found that precipitation is the most sensitive factor affecting the streamflow variation.（2）The Chaohe watershed will exhibit the‘warm and wet’change trend.The annual average temperature and precipitation will increase by 0.83-3.28°C and 8.00-10.30%by 2100,respectively.In addition,the future monthly precipitation changes will exhibit seasonal characteristics.Summer precipitation will exhibit a downward trend impacted by the East Asian summer monsoon,while increasing for the rest of the months.（3）Simulated and predicted the hydrological process found that the future annual streamflow in the Chaohe watershed shows an upward trend.And the increased precipitation was the dominant factor for the streamflow increase.Meanwhile,affected by the intra-annual precipitation variation,the monthly streamflow also showed a downward trend in the summer monsoon（range from-21.51%to-32.60%）.Precipitation,as the vital water supply source,is the dominant factor that caused summer streamflow declination.Predict the streamflow changes under different return period levels,and found that the streamflow at the level of the 5-years return period has increased.Meanwhile,affected by future summer precipitation,the streamflow in 100-year,50-year,and 20-year return periods will decrease.（4）During the historical period,the response of precipitation to warming in the Chaohe watershed exhibited a‘Hook’structure(the peak temperature T_Hook was 22.60°C).With global warming,T_Hookgradually shifts to the right,to some certain extent,releasing the precipitation constraint in the‘Hook’structure.Therefore,the warming response of future precipitation presents a monotonically increasing structure,and the response scale is 6.83-8.82%℃^-1.In addition,the response of streamflow to warming also exhibits the‘Hook’and monotonically increasing two types of structures.Due to the nonlinear response of precipitation to runoff and the influence of the underlying surface conditions,the scale of the runoff to warming response is lower than that of the precipitation response.