Abstract: Land use and land cover change significantly affects climate. To explore the climate effects of cropland expansion, the window search method and the principle of energy balance were used to quantify how the cropland expansion in Northeast china changes the surface energy balance, thereby affecting the land surface temperature based on multi-source remote sensing data in 2000−2018. The results showed that: (1) the area of cropland increased by 1.64×104km2 in Northeast China, mainly from forestland and grassland, accounting for 16.33% and 76.24% of cropland expansion area, respectively. (2) Compared with forestland, cropland has a warming effect on the surface during the daytime, a cooling effect at nighttime, and a warming effect throughout the day with obvious seasonal variation. In summer and autumn, the evapotranspiration of cropland is weaker than that of forestland, and the latent heat flux is less than that of forestland, resulting in a warming effect on the surface. In winter, the net shortwave radiation of cropland is far less than that of forestland, resulting in a cooling effect on the surface. (3) Compared with grassland, the cooling effect of cropland at nighttime is slightly stronger than that during the day, resulting in a cooling effect on the surface throughout the day with obvious seasonal variation. In summer and autumn, the evapotranspiration of cropland is stronger than that of grassland, and the latent heat flux of cropland is more than that of grassland, which has become the main reason for the cooling of cropland to the surface. In spring and winter, the difference of net shortwave radiation absorbed by cropland and grassland is small, leading that the warming/cooling effect on the surface is not obvious.

Key words: Northeast China, Cropland expansion, Biophysical, Energy change