The Impacts Of Land Use And Land Cover Change On Temperature, Hydrological And Energy Budget

The impacts of land use and land cover change (LULCC) on the land surface and tropospheric temperatures, hydrological and energy budgets are investigated in this study using the fully coupled Community Earth System Model (CESM) and the Community Atmosphere Model (CAM). Three simulations are performed using potential, current and no vegetation cover, respectively. The results show that anthropogenic LULCC produces a significant increase of 1-3℃ in the land surface temperature (LST) over South Asia and East Asia throughout the year due to the reduced sensible heat flux and the reduced latent heat flux. In contrast, LULCC leads to a significant decrease in the LST in North America because of the decreased absorbed solar radiation (ASR) due to the increase in the surface albedo. In North Africa, where no clear LULCC occurs, LST still shows a significant decrease due to an enhanced cold advection from Europe to North Africa.It is found that anthropogenic LULCC can also induce detectable changes in the tropospheric air temperature. Although the influence of LULCC on tropospheric temperature is weak, a significant influence can still be found below 300 hPa in summer over land. Compared to the global mean temperature change, LULCC-induced changes in the regional mean air temperature can be 2-3 times larger in the middle-upper troposphere and approximately 8 times larger in the lower troposphere. In East Asia and South Asia, LULCC is shown to produce significant decreases (0.2-0.4℃) in air temperature in the middle-upper troposphere in spring and autumn due to the largest decrease in the latent heat release from precipitation. In Europe and North America, the most significant tropospheric cooling occurs in summer, which can be attributed to the significant decrease in the absorbed solar radiation and sensible heat flux during this season. In addition to local effects, LULCC also induces non-local responses in the tropospheric air temperature that are characterized by significant decreases over the leeward sides of LULCC regions, which include the East Asia-western North Pacific Ocean, the Mediterranean Sea-North Africa, North America-Atlantic Ocean, and the North America-eastern Pacific. Cooling in the leeward sides of LULCC regions is primarily caused by an enhanced cold advection induced by LULCC.The presence of vegetation leads to a significant increase in the land surface temperature and hydrological and energy fluxes at global and regional scales. LULCC-induced changes are region-dependent. For example, the impacts of LULCC on the surface temperature and the downward atmospheric long-wave radiation in South Asia are smaller than those in East Asia, Europe and North America. The ocean-atmosphere coupling effect tends to amplify the impacts of vegetation on the land surface temperature, energy and hydrological budget. LULCC induces stronger cooling due to the greater decrease in the downward atmospheric long-wave radiation when ocean-atmosphere coupling effects are introduced.