The Impact Of Land Use/cover Change On Local Climate Change And Its Mechanism In The Nansi Lake Basin

The impact of Land Use/Cover Change(LUCC)on climate is a research field on the most advancing front in current global change research.As one of the most important and basic factors in ecosystem,climate is of great significance for regional economic development and ecosystem stability.The development of GIS,RS technology and land surface model provides a strong technical support,which can be used to research local influence of LUCC on meteorological elements.The climate change caused by the same land use change type is inconsistent in different regions.Therefore,the analysis that LUCC influences in different regions will provide guidance and theoretical basis for the rational utilization and development of land resources and the improvement of local microclimate in the future.First of all,we analyzed the temporal and spatial distribution characteristics of LUCC based the 1990 and 2015 land use data in the past 25 years.Secondly,we selected from the best scheme from the comparison of 8 methods combined with different parameters.Thirdly,we simulated meteorological elements change which caused by LUCC based on the WRF model.Finally,we analyzed of the mechanism of meteorological elements change effects of LUCC from two aspects,which were land surface parameters and energy flux.The results showed that:(1)In the past 25 years,the main types of land use in Nansi lake basin were cropland,grassland,urban-rural construction land and water area,the most significant characteristic of LUCC are the expansion of urban-rural construction land and the reduction of grassland and marsh grass.Meanwhile,different land utilization types in Nansi lake basin can transfer to each other in different degrees.From 1990 to 2015,urban-rural construction encroachmented on cropland and water area encroachmented on marsh grass were the main characteristic of land use conversion,of which accounted for 18.06%and 12.21%of all land use conversion modes.The rate of change in urban construction land is the fastest,at 6.22%,while that of dry-land farming is the slowest at 0.01%.(2)By using Lin et al.microphysical scheme,rrtm longwave radiation scheme,Dudhia shortwave radiation scheme,YSU boundary layer scheme,New Grell scheme cumulus scheme and Noah-MP land surface process scheme,we can better simulate the temperature and precipitation variation characteristics in 2015.Among them,the correlation coefficient between the simulated temperature and the observed value is relatively high(0.72-0.97,P<0.001).Although the simulation accuracy of the precipitation was lower than that of the temperature,the correlation coefficient between the simulated value and the observed value reached the level of P<0.05.(3)In the past 25 years,temperature has been affected by LUCC and has shown significant temporal and spatial changes.LUCC caused an increase in the average regional temperature throughout the year,in which the average temperature at 2m in the year increased by 0.05?,and the average ground temperature in the year increased by 0.09?.The average temperature changes in the regions where water area encroachmented on marsh grass in January,April,July and October 2015 were 2.1?,-3.7?,-1.4?and 2.6?,respectively,and the average ground temperature in each month changed6.71?,-8.16?,-3.18?and 6.44?.In the regions where urban-rural construction encroachmented on cropland,the mean temperature changes in each month were 1.0?,1.0?,1.4?,and 1.2?,and the average ground temperature changes in each month increased 1.78?,2.39?,4.44?,and 2.27?,respectively.LUCC has a greater impact on precipitation.In the regions where urban-rural construction encroachmented on cropland,monthly rainfall decreased0.11mm,6.41mm,3.5mm,and 0.31mm,respectively.The effects of other land use conversion methods on precipitation vary from season to season.(4)The influence of temperature changes and energy residuals on the change of temperature was analyzed from two aspects.In the area where the water area encroachmented on the marsh grass,the maximum increase in soil moisture was greater than 0.73 in January,April,July and October of 2015.In the regions where urban-rural encroachmented on cropland,the soil moisture in each month has a slight increase,which is less than 0.1.In the area water area encroachmented on marsh grass,the energy residuals were negative in January and October,which were-120.64W/m~2 and-253.39W/m~2respectively.The energy residuals were positive in April and July,which were 189.58W/m~2 and201.17W/m~2.In the regions where urban-rural encroachmented on cropland,the monthly energy residuals are positive,which were 5.99W/m~2,29.1W/m~2,33.79W/m~2,and 14.83W/m~2,respectively.The influence of different land use types on climate can be better explained from these two aspects.The research results can provide the basis and direction for the rational use of land resources in the Nansi lake basin,and provide references for improving the local climate change caused by LUCC.To a certain extent,the research results can enrich the case that LUCC will influence local climate.