Effects Of Winter LUCC On Regional Climate In Northeast China During 1700s?2010s

The study of climate effects of land use/land cover change(LUCC)has always been an important issue of land system science and global change science,and it is also a research hotspot of global environmental change and GLP(Global Land Program).Considering the variability and complexity of global change at different spatial and temporal scales,since the introduction of global change,more and more attention has been paid to the impact of regional differentiation and spatial and temporal changes on the regional natural environment and sustainable socio-economic development.However,up to now,the mechanism of LUCC influencing the climate system through biogeophysical processes at the regional scale has not been fully clarified,especially the impact of surface property changes on the regional climate at mid-high latitudes needs to be further developed.Northeast China is a typical area that has experienced high-intensity intervention by human activities in the past 300 years and the nature of the underlying surface has undergone major changes.It is also the second-largest stable snow area in China and is a typical sensitive area for studying the impact of land cover changes on climate.Based on summarizing and commenting on the research on land cover change and its climatic effects at home and abroad,this paper takes winter land cover change and its resulting climatic effects in Northeast China as the research object from a new perspective and considers snow cover.Combined with the regional climate model(WRF),using statistical analysis,GIS spatial analysis,and other research methods to reveal the temporal and spatial characteristics of land cover in Northeast China under the influence of human activities in the past 300 years.The effects and physical mechanisms of typical land cover changes at mid-high latitudes in winter on regional climate were explored.The study is of great significance in deeply understanding the coupling relationship between land cover change and climate change at mid-high latitudes,enriching and developing the theory and practice of regional environmental change,and promoting the harmonious development of human-nature relationship.The main contents and conclusions of this paper are as follows:(1)Reconstruction of the spatial pattern of land cover types in the Northeast China region in the 1700 s based on historical documents,historical maps,and potential natural vegetation,and analysis of the spatial and temporal variation characteristics of land cover types in the Northeast China region over the past 300 years in conjunction with the CCILC(Climate Change Initiative Land Cover)global land cover dataset.The results show that from the 1700 s to the 2010 s,the land cover type structure in Northeast China has changed significantly,and the areas where the land cover types have changed account for more than 92% of the total area of the region,with forest(mixed forest,broad-leaved forest,coniferous forest),grassland(shrub-grass mixed vegetation,grasslands,shrubs)and swamp decreasing and cropland expanding as the main characteristics of change,among which the forest area has decreased the most,by about 21.52×104km2,followed by grassland and swamp,by 14.70×104km2 and 6.47×104km2,respectively.The land cover change pattern in Northeast China has significant spatial characteristics,as shown by the concentration of forest to cropland in the Greater and Lesser Hinggan Mountains in the northern part of the study area and the Changbai Mountains in the east,the concentration of grassland to cropland in the Songnen Plain in the western part of the study area,and the concentration of swamp to cropland in the Sanjiang Plain in the east.(2)Using MODIS product data to build the spatial and temporal database of winter surface albedo in Northeast China from 2001 to 2020,based on which the correspondence between different land cover types and surface albedo under different conditions(with and without snow)was calculated based on land cover data from 2001 to 2020.The reconstruction of the spatial database of winter surface albedo at the pixel scale in the historical period was completed by combining the recovered land cover data of 1700 s in Northeast China.The spatial differences of winter surface albedo between 1700 s and2010s in Northeast China were also compared and analyzed.The results show that the surface albedo in different winter months in Northeast China in the 1700 s and 2010 s has the spatial distribution characteristics of "high in the plains and low in the mountains",but there are huge differences overall.The kappa coefficients of the surface albedo in November,December,January,and February were all distributed between 0.10 and 0.17,and the spatial distribution characteristics of the surface albedo in winter were consistent with very low.The main difference is manifested in the forest to cropland areas at midhigh latitudes,including the northern part of the Songnen Plain,the southern part of the Greater Hinggan Mountains,and the central part of the Changbai Mountain Range,where the surface albedo increased more significantly,with the highest increase of more than two times.In addition,in the southwestern part of the Songnen Plain(grassland to cropland area),the surface albedo also decreased,but the magnitude of change was much less than that in the forest to cropland.(3)Based on the localized simulation results of the WRF model surface data,the climate effects caused by LUCC in winter in Northeast China and its influence mechanism on climate change were studied.From the simulation results of this paper,the winter LUCC in Northeast China only has effects on the winter climate,in which the winter temperature as a whole shows a cooling effect,with an average decrease of 0.85?in winter,which has a positive mitigation effect on climate warming.The two major land cover change processes,cropland expansion and forest to cropland led to a decrease in winter temperature of 0.41? and 0.13?,respectively,in Northeast China,and the cooling effect of cropland expansion was greater than that of forest conversion to cropland from an overall perspective.The effect of LUCC on winter precipitation in Northeast China was very small,with a slight increase throughout the winter,but the increment was only 0.27 mm.The cropland expansion and forest to cropland caused a small increase in winter precipitation,but the change range in the whole winter was only between 0.2 and0.4 mm,which is almost negligible.In addition,changes in surface properties in the Northeast region strengthened the winter surface wind speed,especially in the forest to cropland areas in eastern Heilongjiang Province,central Jilin Province,and southern and southwestern Liaoning Province.This is mainly caused by the reduction of surface roughness due to the conversion of large areas of dense and towering forests to low and flat cropland.(4)LUCC in Northeast China from the 1700 s to the 2010 s significantly changed the regional winter surface radiation balance and the distribution of energy budget,manifested by a significant decrease in net surface radiation flux,which is mainly due to the increase in surface albedo caused by the expansion of large areas of farmland,increasing reflected shortwave radiation and a decrease in absorbed short-wave radiation at the surface.As a response to changes in net radiation of the surface,sensible heat and latent heat fluxes also changed to varying degrees.The surface sensible heat flux has a relatively large decrease,and although the latent heat flux has also decreased,the change is small.Therefore,the cooling effect caused by the reduction of the sensible heat flux is greater than the warming effect caused by the reduction of the latent heat flux,and the overall cooling effect will still be produced,which explains the general decrease in winter temperature in Northeast China.(5)LUCC in Northeast China has little influence on the surface water vapor flux and the circulation situation in northeast China and its neighboring regions in winter,and Northeast China is located in the East Asian monsoon region,which is controlled by the cold air mass from the northwest direction in winter and prevails northwest wind.At the same time,the vertical upward movement of the atmosphere is not significant in Northeast China due to the low temperature in winter,and the convective activity of the atmosphere is weak,resulting in generally low precipitation in winter,so the influence of land cover change on winter precipitation in Northeast China is tiny.