| The policy of "Grain for Green" launched in 1999 has resulted in a sustained increase in the national forest cover, ecosystem productivity, and carbon sequestration. In the meanwhile, the conversion of farmlands to forests can change the surface albedo, roughness, evapotranspiration, and soil moisture, thereby influencing the hydrology and climate conditions in the region to a certain extent. Due to the complexity of the interactions between the terrestrial biosphere and the atmosphere, how the changes in land cover/land use including urbanization and afforestation influence regional climate is not well understood。Here, NCEP meteorological reanalysis data, gridded air temperature data derived from weather station observation, city extent data, and NDVI trend data were collected. Compared the trends in air temperature and diurnal temperature range (DTR) between the NCEP and the gridded air temperature data on a per-pixel basis and at provincial/national scales. I also compared the trends in air temperature and DTR between urban and non-urban areas and between vegetation greening and browning areas. The results showed that the changes in land cover/land use in China significantly influenced regional climate. Urbanization had a positive effect on the warming trend, while afforestation including the "Grain for Green" Program slowed down the increase of air temperature to some extent.The contents of the research include:(1) 2000 is a key node, before 2000, the regional climate in China shows significant upward trend of this trend can be attributed in part to fast city urbanization. After 2000, urbanization entered the new stage, and returning farmland to forest policy launched. Both of these two factors have an inhibitory effect on the rising trend of air temperature and the effective influence on the ecological environment. In recent years, the restoration of the ecological environment has made the temperature drop.(2) Temperatures in the northwest region in the implementation of the grain also forest project has decreased, returning farmland to forest the land use for the climate to stabilize climate change makes the change trend of air temperature in Northwest with global warming, the trend was reversed. In the Middle East, the process of urbanization significantly increases the local temperature, but the trend of rising temperatures is less than the global trend, which can be attributed to the regional climate has its own unique stability.(3) Land use change to a certain extent, the impact of the season on climate change. Urban and non urban areas, the two seasons of winter and summer is obviously different, the urban area is not purely by anthropogenic heat effect and higher than in rural areas. In winter, the city area has appeared more cold than rural conditions. But the overall trend of the two is the same, there are common patterns of change, which is hot in summer and cold in winter.In general, the effect of land use pattern on the regional climate is obvious. Under the environment of global warming, the change of the land use pattern, which is changed from the natural environment to the artificial environment, will increase the global warming, such as urbanization.At the same time, the change of the land use mode from the artificial environment to the natural environment has delayed the process of global warming. Since the implementation of the policy of returning farmland to forest, the trend of regional warming has been improved. |
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