Simulation And Prediction Of The Influence Of Farmland Land Use Change On Surface Water And Heat Transfer In Sanjiang Plain

Sanjiang plain is located in the seasonal frozen soil area of China.There are large areas of wetlands.Since 1950,due to the large-scale reclamation of human beings,the area of wetland began to decrease sharply,and a large area of wetland was cultivated into farmland,woodland and other land use types.The change of land use pattern has great influence on regional microclimate,surface runoff,groundwater level and soil freeze-thaw.The regional annual average temperature shows an upward trend,the annual average precipitation shows a downward trend,and the overall climate shows a warm and dry trend.Moreover,the change of land use leads to the decrease of surface runoff and the rapid decrease of groundwater level.Considering Sanjiang Plain as the study area,this study explored the influence of land use change on soil water and heat transport and the future trend of surface water and heat transport.This provides the counter measure for the future agricultural production development.The effects of land use change on soil water and heat transport were revealed using observation data from the Sanjiang Mire Wetland Experimental Station of the Chinese Academy of Sciences from the period of May 2016 to May 2017.The analysis found evident changes in the water and heat status of different land use types.During conversion from upland to paddy field,the surface soil moisture content increased,evapotranspiration increased by approximately 40%,surface infiltration increased by about 20%,and surface heat flux decreased.The surface water and heat flux of upland and paddy fields were simulated by using the hydrothermal coupling model(SHAW model).The simulation efficiency of soil temperature is greater than that of soil moisture content.Due to the influence of leaf area index of different crops,the annual surface evapotranspiration in paddy fields is greater than that in upland fields,and the surface infiltration in paddy fields is greater than that in upland fields due to the differences in soil particle size composition,organic matter content and farming methods.During the transformation from upland to paddy field,due to the variety of cultivated crops,the leaf area index of plants increases and the surface evapotranspiration increases.And in April,the initial evapotranspiration of soil surface decreased.Due to different farming methods,soil organic matter content will increase,soil surface clay ratio will decrease,soil infiltration rate will increase,and surface infiltration will increase in the growing season.The change of land use pattern leads to the increase of average annual temperature of surface soil,the decrease of temperature difference with air temperature,and the decrease of soil heat flux.And the time delay to reach the minimum heat flux is about 25 days.In a future climate change scenario,the change trend of soil water and heat condition was roughly consistent with the present situation,and the proportion of evapotranspiration of upland and paddy fields in precipitation decreased to 40% and 55%,respectively.These results can provide reasonable countermeasures for the future agricultural production in Sanjiang Plain.