Characteristics And Mechanisms Of Hydrological Cycle In Different Climate Regions Of China Under Global Warming

Global warming is accompanied by dramatic changes in the hydrological cycle.Warming increases the water holding capacity of the atmosphere,which leading directly to a rapid increase in water vapor,while the feedbacks of other components of the hydrological cycle are more complex.The significant increase in evapotranspiration(ET)in recent years has caused frequent drought and urban heat waves,but the evolution of ET is limited by both evaporative demand and surface water and is difficult to assess.Extreme precipitation is one of the most serious consequences of climate change,the large local variability in cloud and precipitation processes is a major source of model uncertainty.Particularly in the monsoon-influenced East Asian China,where there are huge differences in water resource evolution among different climatic regions.The climatic feedbacks of the water cycle are extremely complex and there are large uncertainties in quantitative descriptions.Research on the feedback mechanism of water cycle in different climate zones of China under global warming can provide scientific support for disaster prevention and mitigation,artificial weather impact,etc.which is vital for ecological environment,agricultural production,and human life.The evapotranspiration,cloud water resources and precipitation efficiency in China,as well as the dynamic and thermodynamic feedback of extreme precipitation on warming were analyzed in this paper.The results and conclusions include:(1)The evolution characteristics of evapotranspiration in different climatic regions of China around 1998 and its influencing factors were discussed.The national average ET showed an overall increasing trend of 0.665 mm/day/year,and there was significant interdecadal variation.ET were decreasing until 1998 and started to increase significantly after 1998,which is the opposite of the evolution of global ET.Empirical orthogonal decomposition of ET was carried out by dividing China into two regions constrained by water supply(water-limited region)and atmospheric evaporation demand(energy-limited region).The significant increase in potential evaporation from the southern humid zone was found to be the main cause of interdecadal variation in evapotranspiration in China around 1998.The explained variance of the first principal component of ET in the energy-limited region reaches 57.3%,which mainly shows significant interdecadal variability and is mainly controlled by the warming context.In contrast,ET in the water-limited region showed mainly interannual variability controlled by precipitation.This different feedback of evapotranspiration from the north and south regions to climate change is also manifested in the difference in the distribution of surface energy.There was an overall significant trend of decreasing Bowen Ratio in arid and semi-arid regions,but the large difference between summer sensible and latent heat flux in arid regions will continue to increase.(2)Cloud water content over China was assessed using MOD08＿M3 data,and the mechanisms that produce differences in the cloud-precipitation under different regions were explored in terms of both dynamical and thermodynamic contributions.National average liquid and ice water path of 157.47 and 240.24 g/m~2,respectively,from 2001-2019.The overall trend of liquid water and ice water path in the last two decades was a significant decrease of-3.3 and-4.89 g/m~2/decade,and the trend of decrease is more obvious in the wetter areas with higher precipitation.The annual average of cloud water period in China is about 12.4 hours,and its seasonal variation is obvious with huge differences in winter and summer.The cloud water period decreased significantly throughout the arid zone and did not change in the humid zone.Due to the overall small upward moisture flux(UMF)in the arid zone,the feedback of the cloud water period on the lower-troposphere stability(LTS)mainly takes the form of an increase followed by a decrease,which is completely opposite in the humid zone.The situation of UMF remains unchanged,and the continuous decrease of LTS in the northwest arid zone is the main reason for the continuous decrease of the cloud water period.The different configurations of UMF and LTS play an important role in the differences in the evolution of cloud-precipitation in arid and humid zones,which can be used to some extent as a diagnostic basis for determining the evolution of precipitation.(3)The effects of convective activity and warming-sensitive experiments on cloud-precipitation efficiency during a storm corridor event in July 2020 were analyzed using the WRF model.The two precipitation processes from July 4-6 formed a west-to-east rain belt in the Jianghuai basin,and the accumulated precipitation exceeded 300mm.The cold and warm air masses in the troposphere were bounded by the 350 K equivalent temperature contour and converge near 30°N to form a front.Warm and humid air masses were constantly lifted and condensed to form precipitation.Southwest winds carrying a constant stream of warm and humid air is a direct source of precipitation.The warming will strengthen the north-south potential temperature gradient and create a stronger upward movement on the front.It also strengthens the southwest winds to transport more water vapor to lift and condense on the fronts,resulting in stronger precipitation peaks.The intensification of convective activity and the acceleration of latitudinal winds advanced the onset of precipitation processes.Both convective available potential energy(CAPE)and convective inhibition energy(CIN)intensity increased sequentially with increasing temperature,and convective instability energy accumulation and release are more intense after warming.The precipitation efficiency increased with increasing temperature in the three experimental groups,15.85%,17.68%and 19.20%,respectively.Warming will modify cloud precipitation processes and precipitation efficiency by promoting and suppressing convective activity simultaneously,which may also account for the enhanced extreme precipitation in a warming context.The diagnostic relationship between UMF and LTS on precipitation intensity was corroborated from the perspective of a single rainfall process using the WRF model.(4)The observation-based surface precipitation temperature dataset in China was used to analyze the evolution form of precipitation in China in the past two decades.And the physical scale diagnostics were used to decompose the scaling of extreme precipitation in China into dynamic and thermodynamic contributions.The average daily precipitation in China only had a relatively small trend of 0.10 mm/day/decade under global warming,while the amount and frequency of heavy precipitation have both increased significantly.On the contrary,the frequency of weak precipitation decreased,and the distribution of precipitation gradually changed from light precipitation to heavy precipitation.The variation of annual maximum daily precipitation was an increasing trend of 3.13 mm/day/decade on the national average,and the feedback on temperature varies widely regionally,with the scaling rate in the range of 0～5%/°C in most of western and northern China.The scaling rate were generally higher than twice the C-C rate mainly in the southeast where the precipitation is higher.The 75%,90%and 99%extreme precipitation all increase exponentially with increasing temperature and begin to decrease after a certain threshold(about 20°C)is reached.The thermodynamic contribution was overall more evenly distributed across the country,with most areas close to the C-C rate(6.41%/°C).The national average of dynamic contribution was about 2.30%/°C,but its regional variation is large.The dynamic contribution can be up to twice the C-C rate in south-eastern China,while negative feedback exists in the northwestern region.Dynamic contributions were the main reason for the large regional differences in the distribution of extreme precipitation.