Simulation Study On The Climatic Effects Of Agricultural Development Over Songnen Plain In The Last Century

As an important commodity grain base in our country, Songnen Plain has experienced a large-scale agricultural reclamation in the past hundred years. Although the large-scale agricultural development is propitious to the development of the local social economic and the food security of the country, but which led the decrease of grass and other natural vegetation coverage area. The profound changes in land cover have a profound impact on the local climate. To reveal the effect of agricultural reclamation on climate of Songnen Plain in the past one hundred years, this paper simulated the Songnen Plain agricultural reclamation influence on local climate based on the foundation data of high spatial resolution history land use/cover reconstruction with the improved WRF/Noah-MP model, the main conclusions are as follows:(1) In the past hundred years, the land use/cover change of Songnen Plain trend to the increase of cultivated land and the decrease of the grass. Specifically, the cropland area increased from 46507 km2 to 117772 km2 with the growth amplitude of 153.23%, while the grassland area decreased from 102947 km2 to 17107 km2 with the reduce amplitude of 83.38%. Besides, there was a turn point in the land use/cover change of Songnen Plain in 1970 s. The cropland area increased rapidly at the rate of 0.713×103 km2 per year, while the grassland area decreased with the rate of 0.858×103 km2 per year before 1970 s. After 1970 s, the cropland growth and grass reduce rate dropped significantly, the growth rate is 0.973×102 km2 per year and the reduce rate is 0.522×102 km2 per year.(2) The localization of subgrid and leaf area index in WRF/Noah-MP model has reduced the root mean square error of simulated and observed temperature, The highest amplitude is 0.6 ℃; it improved the model simulation of land surface temperature performance. The simulation accuracy of the surface temperature spatial distribution is obviously improved in Songnen Plain western region.(3) From 1910 s to 2010 s, the extension of cropland and the replacement of natural grassland has increased the leaf area index in the summer half year. The increase of leaf area index led the increase of land surface albedo and the decrease of the surface net solar radiation. Meanwhile, the surface sensible heat flux increased largely, while the surface latent heat flux decreased. As a result, there was also a heating effect of agricultural reclamation on local surface climate. The surface temperature in southern of Songnen Plain and Nenjiang River is increased significantly and in the middle of Songnen Plain is decreased obviously, the average vary amplitude is 0.42℃ and 0.45℃ respectively. In addition, the precipitation of the summer half year overall showed a decrease trend in Songnen Plain. Specifically, the decrease of precipitation is obvious in the central and northern of Songnen Plain, the average decrease amplitude is 0.46 mm/day. However, for the smaller scale of agricultural reclamation in the winter half year, so there is no obvious change in the land use/cover, local surface temperature and precipitation.