Biogeophysical Impacts Of Large-scale Ecological Programs On Regional Climate In China

Excessive deforestation in China has led to decreased forests,land degradation,and even natural disasters including droughts,floods and sandstorms,which have threatened the state property and people's life.In order to solve the increasing ecological and environmental issues,China has carried out a series of large-scale ecological programs in the last 4 decades,including the "Three-North Shelterbelt" and"Grain for Green".Benefiting from these ecological programs,China's forest has been restored and to some extent improves the ecology and environment.In addition to ecological and environmental benefits,afforestation can impact local and regional climate through biophysical processes.However,the biophysical impact of afforestion on climate in China was rarely examined before and consequently remains large uncertainties.Based on existing studies,we raised 3 key questions which need to be addressed.? How does the afforestation in China impact the local temperature through biophysical processes?? How does the revegetation over the Loess Plateau of China impact the hydrological cycle and the sustainbility of water resource?? Do the uncertainties in the land cover classification impact the simulation of temperature and rainfall over East Asia?We obtained the following main conclusion from our studies:? The non-radiative effect dominates local surface temperature change caused by afforestation in China.We investigated the local impact of afforestation by comparing adjacent forest and open land pixels using satellite observations between 2001 and 2012.We attributed local surface temperature change between adjacent forest and open land to radiative and non-radiative effects over China based on the Intrinsic Biophysical Mechanism(IBM)method.Our results reveal that forest causes warming of 0.23(±0.21)? through the radiative effect and cooling of-0.74(±0.50)? through the non-radiative effect on local surface temperature compared with open land.The non-radiative effect explains about 79(±16)%of local surface temperature change between adjacent forest and open land.The contribution of the non-radiative effect varies with forest and open land types.The largest cooling is achieved by replacing grasslands or rainfed croplands with evergreen tree types.Conversely,converting irrigated croplands to deciduous broadleaf forest leads to warming.This provides new guidance on afforestation strategies,including how these should be informed by local conditions to avoid amplifying climate related warming.? The revegetation of the Loess Plateau of China is likely to cause a negative impact on the sustainbility of water resource.We investigated the impact of revegetation on the hydrology of the Loess Plateau using relatively high resolution simulations and multiple realisations with the Weather Research and Forecasting(WRF)model.Results suggest that revegetation since the launch of the GFGP has reduced runoff and soil moisture due to enhanced evapotranspiration.Further revegetation associated with the GFGP policy is likely to increase evapotranspiration further,and thereby reduce runoff and soil moisture.The increase in evapotranspiration is associated with biophysical changes,including deeper roots that deplete deep soil moisture stores.However,despite the increase in evapotranspiration our results show no impact on rainfall.Our study cautions against further revegetation over the Loess Plateau given the reduction in water available for agriculture and human settlements,without any significant compensation from rainfall.? The uncertainties in the reconstruction of land cover hardly affect the simulation of air temperature and rainfall in the CORDEX region of East Asia.We used the Weather Research and Forecasting(WRF)model to determine whether these misclassifications can affect the simulations of air temperature and rainfall over the Coordinated Regional Climate Downscaling Experiment(CORDEX)East Asia region,where the accuracy of the land cover classification is low.The Moderate Resolution Imaging Spectroradiometer(MODIS)land cover map was used for the control simulations,and was then replaced by the most likely alternative land cover type at pixels where the classification confidence is below various threshold values.Results show that misclassification induced land cover change can affect key biogeophysical characteristics(albedo,leaf area index and roughness length)and these can affect the sensible and latent heat fluxes at regional scales.However,the impact on air temperature is very limited and is restricted to the Tibetan Plateau where warming of up to 2? occurs associated with the replacement of barren or sparsely vegetated land to grassland.The impact on rainfall is negligible,and most changes are likely caused by model internal variability rather than land cover change.Overall,uncertainties in the reconstruction of land cover have negligible impacts and the MODIS land cover product can be used in regional simulations over East Asia.However,we note that land cover change experiments incorporating uncertainties must utilise large numbers of simulations if air temperature and rainfall changes are to be examined robustly.