| Land use and cover change also its climatic effects are important topics in current land ecology research.In the cold regions of the middle temperate zone,the low temperature environment causes the growing season crops to show high sensitivity to temperature.As a result,surface temperature has become an important factor affecting agricultural production in the region.Changes in the surface of cultivated ground can significantly change the surface radiant energy flux,affect the surface energy balance process,and change the regional surface temperature,thereby affecting crop growth and agricultural production.The northern part of the Sanjiang Plain is an important food production base in the middle temperate zone of China.In the context of global warming,the paddy field boundaries in the region have shifted significantly northward,paddy fields have expanded drastically,and the conversion of cultivated land underlays significantly.At present,there have been many achievements in characterizing the paddy field expansion process in the Sanjiang Plain.However,there is still no specific discussion on the characteristics of the impact of the conversion of cultivated land on the surface temperature.Therefore,it is crucial that learn the relationship between paddy field size and spatial characteristics and surface temperature in the northern Sanjiang Plain,and clarifying the impact of paddy field expansion on regional surface temperature based on the perspective of land ecology,to deepen the understanding of the current regional land use and cover changes in regional climate effects and scientifically respond to the global climate changing,as well as realize the goal of sustainable land use in land ecology has important theoretical and practical significance.From the perspective of land ecology,this paper takes the northern part of the Sanjiang Plain in the cold region of China as the research area,and takes the spatiotemporal pattern of paddy fields and the surface temperature as the research objects.By using administrative division data,remote sensing data such as Landsat 8 OLI/TIRS data and MODIS data and cultivated land use data,implementing remote sensing technology methods,geospatial analysis methods,statistical analysis methods,and correlation analysis methods,the study has completed the discussion on the effects and laws of paddy fields on surface temperature,and the specific feedback characteristics of the climatic elements of the farmland system during the paddy field expansion process.The main research contents and results of this article are as follows:(1)Using inversion surface temperature data and cultivated land utilization data as data sources,the study used statistical analysis methods of different scales to analyze the difference between the surface thermal environment of paddy fields and dry land,and analyzed the effect mechanism of paddy field size on instantaneous surface temperature by correlation mechanism.The results showed that the paddy field has a significant effect on the instantaneous surface thermal environment,and the paddy field size has a significant negative correlation with the instantaneous surface temperature.During the study period,with the increase of the proportion of paddy field area,the average value of regional surface temperature showed a clear decreasing law,and paddy field cultivation would have a cooling effect on the surface temperature.As far as the degree of correlation,the correlation coefficient between the percentage of paddy field area and the average surface temperature exceeded 0.9,and the size of the paddy field on the village scale(about 1400 hm~2)had a significant cooling effect on the surface temperature.(2)Taking the kilometer grid as the basic statistical unit,during the statistical analysis of the effect of the paddy field pattern on the surface temperature in different months of the main growth period of the crop,it was found that there are differences in the cooling effect of the paddy field at different crop growth stages.During May-October in 2017,the monthly value of cultivated land LST increased first and then decreased,with the peak in June and the lowest in October.On the scale of 1km grid unit,the monthly mean value of LST and the proportion of paddy field area within the cultivated area of the study area showed a significant negative correlation at the level of0.01 from May to October.The fitting results of the relationship between the paddy field level and the monthly mean surface temperature indicated that the linear relationship,the quadratic function relationship,and the cubic function relationship all showed a high degree of fitting,of which the cubic function relationship showed the highest fitting degree,rather the linear relationship fitting ratio was relatively lower.As the size of the paddy field increased,the surface temperature showed a non-uniform decreasing trend,and the cooling effect of the paddy field was increasing.During the uniform increase of the paddy field size,there was a clear threshold-type characteristic of the surface temperature cooling intensity.When the paddy field ratio reached 8(the ratio of paddy field area to the total cultivated land area more than 80%),the difference change rate was higher than the average change in each month.In addition,the paddy field had different degrees of influence on surface temperature at different periods of the crop growing season.The average rate of change in temperature difference between May and June was large.At this time,the LST value was most sensitive to changes in the pattern of paddy.(3)In the investigation of the mechanism about the impact that paddy field expansion had on the surface thermal environment over a long period of time,the research mainly used quantitative analysis methods such as dynamic degree,a series of spatial analysis methods of gravity center shift,and coupled analysis methods such as calculation of contribution index and cooling intensity index.The conclusion showed that from 2000 to 2015,the use of cultivated land in the study area changed significantly,massive transformation of dry fields into paddy fields happened.The scale of paddy fields increased significantly,and they showed an outward expansion and a northeastward shift of the center of gravity in the space.Rapid and large-scale changes in underlying surface had significantly affected the characteristics of the surface thermal environment.Average daytime surface temperature of the cultivated land during the crop growth period in the study area showed a significant downward trend,and the temperature anomaly changed from a positive value to a negative value,the range of low-temperature and sub-low-temperature regions expanded,and high-temperature ones decreased significantly,which corresponded to the changes in the size of paddy fields and dry land,respectively.At the same time,the center shift of the low-temperature region showed a high consistency with paddy gravity center,while the path of the high-temperature region center shift is opposite to the shift direction of paddy gravity center,and the spatial structure characteristics change significantly.During the whole period,the contribution index of the paddy field to the average surface temperature of the cultivated land was negative,and as the proportion of the paddy field area increased,the absolute value of the index increased,and the cooling intensity of rice paddy continued to increase.Overall,this paper combined quantitative analysis and spatial analysis methods,and based on the coupling analysis,realized the discussion of the evolution process and regular characteristics of local surface temperature in the process of paddy field expansion,then explained the impact of human activities such as cultivated land use changes to local meteorological factors from the perspective of land ecology.We also explore the characteristics of the environmental effects of changes in cultivated land use in cold regions in combination with crop phenological characteristics.Results of the study showed important theoretical reference significance for ecological attention and countermeasure design in terms of optimal allocation of cultivated land resources. |
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