Historical Reconstruction And Projections Of Land Surface Albedo Changes In China From 850 To 2100

Land surface albedo is a critical parameter of the Earth's radiation and energy budget,which has been greatly altered by the global climate change and human activities at global and regional scales.In the satellite remote sensing era(1970s to present),the spatiotemporal variations of land surface albedo have been monitored by satellite observations.However,because land surface albedo before the satellite era and future scenarios cannot be directly acquired by measurements,historical/future land surface albedo changes must be obtained using reconstructions and model simulations.To improve our understanding of historical/future land surface albedo changes and their climatic effects,we reconstructed and projected the land surface albedo from 850 to 2100 in China using the historical land use harmonization version 2(LUH2)dataset and albedo look-up maps,and estimated the radiative forcing induced by land surface albedo changes with the atmospheric radiative kernels.The main findings of this study are listed as follows,(1)The annual-mean historical land surface albedo in China increased from 0.20747 to0.20855(an increment of 0.00108)during 850–2015,and the rate of increase was accelerated by the growth of croplands over recent centuries.The evolution of historical land surface albedo in China can be characterized by five phases of development:In the first phase(between the 9th and 10th centuries),the land surface albedo remained nearly stable;The second phase of development was a rapid increase in land surface albedo during the 11th and12th centuries.In the third phase(between the 13th and 14th centuries),annual-mean land surface albedo decreased due to the wars between the Song,Jin,and Yuan Dynasties,as well as the damage and destruction of the agriculture-based economy during the period of the Yuan Dynasty.The fourth phase was a period of increasing land surface albedo during the Ming Dynasty and early Qing Dynasty(between the 15th and 17th centuries).The fifth phase was another period of increasing land surface albedo that lasted from the early 18th century to the present,the land surface albedo of China increased with a much higher rate(+0.00029/century)than that of earlier periods.The 20th century is the most rapid period of land surface albedo change(+0.00060/century)in the historical record.Significant increases in land surface albedo occurred in the northern and eastern part of Songnen Plain,the Lesser Khingan Mountains,Sanjiang Plain,Huabei Plain,Yili River Valley,and the eastern part of Qinghai-Tibet Plateau,and significant decreases in land surface albedo occurred in the central Songnen Plain,the farming-pastoral ecotone of China,the Sichuan Basin,and the lower reaches of the Yangtze River.The most significant increases in land surface albedo were found in the Huang-Huai-Hai(HHH)(+0.00626)and Northeast China(NE)(+0.00502)agricultural zones,which can be largely explained by anthropogenic land cover transformations(land reclamation,deforestation,and urbanization)and the vegetation masking effect on snow cover.(2)The radiative forcing induced by land surface albedo in China during 850–2015 and1750–2015 were-0.08±0.04 and-0.06±0.02 W m^-2,respectively.The negative radiative forcing induced by land surface albedo changes indicated a climate cooling effect,which helps offset the warming effect caused by greenhouse gas emissions.The most significant radiative forcing effect during 850–2015 occurred in HHH(-0.60±0.28 W m^-2),and the most significant radiative forcing during 1750–2015 occurred in NE(-0.22±0.06 W m^-2).(3)Eight Representative Concentration Pathways-Shared Socioeconomic Pathways(RCPs-SSPs)were used for denoting the future scenarios in the Coupled Model Intercomparison Project,Version 6(CMIP6).The future projected land surface albedo in China from 2015 to 2100 increased in the scenarios of RCP3.4-SSP4 and RCP3.4OS-SSP5,kept nearly stable in the scenario of RCP8.5-SSP5,and decreased in the scenarios of RCP4.5-SSP2,RCP6.0-SSP4,RCP7.0-SSP3,RCP1.9-SSP1,and RCP2.6-SSP1(ascending by decreasing rate).(4)The temporal trends of radiative forcing induced by surface albedo changes are opposite with the temporal trends of surface albedo changes.The negative radiative forcing induced by land surface albedo changes in the scenarios of RCP3.4-SSP4 and RCP3.4OS-SSP5 indicated a cooling climate effect;The positive radiative forcing induced by land surface albedo changes in the scenarios of RCP4.5-SSP2,RCP6.0-SSP4,RCP7.0-SSP3,RCP1.9-SSP1,and RCP2.6-SSP1 indicated a warming climate effect.(5)The main improvement of the reconstruction and projection method are:LUH2 data allowed us to extend the analysis back to 850,thereby enabling the reconstruction of land surface albedo changes before the industrial era and future scenarios;the spatial resolution of the land use dataset was significantly improved(0.25?)was significantly improved compared to previous studies,which enabled us to derive spatial patterns of historical land surface albedo changes with higher spatial resolution.In this study,the land surface albedo changes in China from 850 to 2100(historical era from 850 to 2015,and eight RCPs-SSPs scenarios from 2015 to 2100)were reconstructed and projected,and their climate effects were estimated with the atmospheric kernel method.The findings of this study can provide theoretical and policy basis for the environmental protection and climatic engineering in the future.