Regulatory Mechanisms And Rules Of Regional Water Condition On Surface Air Temperature

Regional water condition as one of driving factors impacting the coupled soil-vegetation-atmosphere system, regulates the system energy balance as well as near-surface air temperature(hereafter referred to as temperature). Currently, two kinds of different explanations exist on the process through which regional water condition impacts temperature. One is that the change of regional water condition changes temperature through land surface processes and coupled water and energy balance; the other is that the regional water condition variation leads to surface radiation change firstly, and then it affects temperature. Therefore, it becomes an attractive topic to researchers on mechanisms and characteristics of water condition impact on temperature. To address this issue, surface radiative component changes when regional water condition regulates temperature have been identified. The regulatory mechanisms, distribution characteristics and sensibility of regional water condition on temperature have been explored. Finally, impacts of regional water condition to ecologic system and temperature in the Heihe River basin(HRB) have been studied. The following conclusions have been generated:Based on the principles of coupled water-energy and surface energy balance, the regulatory mechanisms of water condition(the precipitation is taken as a surrogate indicator of water condition) on temperature have been revealed through a large number of data analysis on meteorology, hydrology and surface radiation. In dry environments, the precipitation decrease leads to evapotranspiration decrease(i.e. lower latent heat flux and higher sensible heat flux), finally results in evaporative cooling reduction and temperature increase; while in humid environments, the relationship between temperature and precipitation is not significant; although solar radiation increase provides the potential heat source for increasing temperature, different partition ways in dry and humid environments result in different temperature variation characteristics; Since temperature variation characteristic due to precipitation change is significantly different from that due to greenhouse gase effects, it may be possible to further explore temperature variation causes from the change of radiation.Two masks have been proposed to effectively filter and obtain the global grids which are covered with meteorological stations and free of snow or ice cover. At pixel level, the statistics have been made on the relationship between water condition and temperature as well as the response of surface radiative components to precipitation. Moreover, their distribution characteristics have been investigated under global scale. In dry environments, evapotranspiration plays a crucial role in interactions between temperature and precipitation. Three typical flat regions are selected to analyze the relationship between regulation magnitude of precipitation variation on temperature and the effect of precipitation on evapotranspiration. The results indicate that the higher the effect of precipitation on evapotranspiration, the larger impacts of precipitation on temperature and radiative components. It implies that a stronger soil-atmospheric interaction with precipitation change exists in dry environments than that in humid environments.The HRB is selected as the study area to analyze the regulation impact of water condition(the precipitation and runoff changes are taken as water condition variation resulted by climate change and human activities). The contributions of climate change and anthropogenic activities on runoff variation have been identified based on the principle of coupled water-energy. The impacts of water condition variation on vegetation cover and temperate in the lower basin are evaluated through analyzing the remote sensing and long-term hydrological data. The results indicate that water condition variation has positive impacts on both temperature and eco-system in the lower HRB after the implementation of the near-term environmental conservation program since 2001, characterized by the higher vegetation cover and the lower temperature increase rate.