Changes Of Surface Albedo And Its Radiation Effects Caused By Land Use Change

In order to study the changes of surface spectral albedo and its radiation effects caused by land use change in different periods,the LUH2 datasets from 1860 to 2060 are statistically analyzed.The long-term change trends and spatial distribution characteristics of surface spectral albedo are calculated in different periods of the world and typical regions.Finally,BCC?RAD model is used to calculate the effect of land use change on radiation in different periods.The main conclusions are as follows:Seasonal albedo variations of 17 IGBP-classified land use types in visible,near-infrared and short-wave wavelengths are obtained.The visible reflectance of snow/ice surface and waterbody is the strongest,and the visible albedo of snow/ice surface can reach 0.9231.The surface spectral albedo of other land use types mainly shows as near-infrared>short-wave>visible light.In addition,the spectral albedo of different land use types is different,and the seasonal mean of spectral albedo of the same land use type also has obvious spatial difference.The spatial distribution characteristics and seasonal change trends of the spectral albedo caused by the main land use type changes in the four typical regions are obtained.Since 1860,the surface spectral albedo of typical areas has shown a consistent seasonal variation trend.Between 1860 and 1900,the increase in urban and crop in typical areas led to an increase in the spectral albedo.Among them,the Mid-east United States increased the most,with the largest increase in visible albedo being 0.0064.From 1900 to 1950,the visible albedo of the grasslands in Eastern China decreased significantly(0.0094);but the spectral albedo of other places showed an increasing trend.From 1950 to 1980,crop in Eastern China began to decrease;evergreen coniferous forests and mixed forests in Southeast Europe began to increase;all forest types and all types of wasteland in Mid-east United States gradually increased;and crop and urban areas in Southern Brazil continued to increase.In 1980?2000,crop in Eastern China continued to decrease;natural vegetation and urban areas in Southeast Europe gradually increased;savannas,open shrubs,grasslands,and urban areas in Mid-east United States increased significantly;mixed forests began to increase in Southern Brazil.From 2000 to 2015,crop and urban areas in the four typical regions continued to increase.From 2015 to 2030,under the RCP2.6 scenario,the urban gradually increases and the crop gradually decreases in the four typical regions;under the RCP4.5 scenario,the natural vegetation shows a gradual decrease in Southeast Europe and Southern Brazil,while deciduous broadleaf and mixed forests in Eastern China and Mid-east United States begin to gradually increase;under the RCP6.0 scenario,closed shrubs begin to increase in Southeast Europe,while natural vegetation shows a gradual decrease in Eastern China,Mid-east United States,and Southern Brazil;Under the RCP8.5scenario,the natural vegetation in the four typical areas is gradually reduced,and the crop continues to increase.From 2030 to 2060,the deciduous broadleaf in the four typical regions all shows an increasing trend under the RCP2.6 scenario;under the RCP4.5 scenario,the urban areas in Eastern China and Mid-east United States continues to increase,while The natural vegetation and urban areas are gradually decreasing in Southeast Europe and Southern Brazil;under the RCP6.0 scenario,the crop gradually increases in Eastern China,Southeast Europe,and Mid-east United States,while the crop gradually decreases in Southern Brazil;in RCP8.5scenario,deciduous broadleaf are increasing obviously in Eastern China,Southeast Europe,and Mid-east United States,while evergreen broadleaf and mixed forests in southern Brazil gradually increase.The radiative forcing caused by land use changes in different periods is calculated by using the BCC?RAD radiative transfer model,and it is found that the average global radiative forcing in different periods is all negative,showing a cooling effect.In 1860?1900,the four typical areas all showed the conversion of natural vegetation to human land.The maximum negative radiative forcing in Southeast Europe is-0.9647W/m~2,and the minimum in Southern Brazil is-0.021W/m~2.In 1900?1950,the four typical areas all showed a continuous increase in crop and urban areas.However,the radiative forcing caused by changes in visible albedo in Eastern China were positive,while the other three regions had negative radiative forcing.From 1950 to1980,all forest types,crop,urban areas,waterbody,and permanent wetlands in the world gradually increased,resulting in negative radiative forcing;crop in Eastern China began to decrease,resulting in positive radiative forcing.From 1980 to 2000,the radiative forcing in Eastern China and Southern Brazil was negative,while the radiative forcing in Southeast Europe and Mid-east United States was positive.Among them,the crop in Southern Brazil continued to increase,while the rest of the regions showed a trend of decreasing.From 2015 to2030,the radiative forcing in Eastern China under the RCP4.5 scenario is negative(-0.1845W/m~2);Southeastern Europe is negative under the RCP4.5 and RCP8.5 scenarios(-0.2702 W/m~2 and-0.0017 W/m~2);the Mid-east United States is negative under the RCP2.6scenario(-0.0494 W/m~2);while the annual mean of the radiative forcing in Southern Brazil under the RCP2.6 scenario is positive(0.0477W/m~2).Among them,under the RCP2.6 scenario,the four typical areas show a gradual decrease in crop,and the urban area gradually increases;under the RCP4.5 and RCP6.0 scenarios,the four typical areas have a gradual increase in crop;Under the RCP8.5 scenario,Southeast Europe,Mid-east United States,and Southern Brazil all show the conversion of natural vegetation to urban area.From 2030 to 2060,the radiative forcing in Eastern China under the RCP4.5 scenario is negative(-0.1111W/m~2);Southeast Europe is negative under the RCP2.6 and RCP4.5 scenarios(-0.0361W/m~2 and-0.1173W/m~2);the Mid-east United States are positive under the four future scenarios;Southern Brazil is positive under the RCP6.0 scenario(0.0539W/m~2).Among them,under the RCP2.6 and RCP4.5scenarios,the forest and urban area in Eastern China and the Mid-east United States gradually increase,and the crop in Southeast Europe and Southern Brazil continues to increase;under the RCP6.0 scenario,the crop in Southern Brazil begins to decrease,while in the rest of regions gradually increases.Under the RCP8.5 scenario,the natural vegetations in Southeast Europe gradually decreases,the urban area in Eastern China and Mid-east United States gradually increases,while the urban area in Southern Brazil gradually decreases.