| The research on the dynamic process,evolution mechanism,and environmental impacts of crops' spatio-temporal pattern is currently a hot issue in the field of global change and environmental sustainable development.The information of crops' spatio-temporal patterns reflects the human use of land resources in space,which is an important basis for studying the impacts of farmland ecosystems on food production systems and the ecological environment.Wheat is the most widely distributed food crop in the world,and its spatial distribution pattern has an extremely important impact on global food security and the global ecological environment.However,the current research on the dynamic process,impact mechanism and ecological impacts of wheat spatial pattern has been rarely studied,which limits the reasonable allocation of wheat distribution and optimal management of agricultural resources.Therefore,how to analyze the dynamic process,influence mechanism,and environmental impacts of wheat spatial pattern,so as to optimize the wheat planting and agricultural production resources is a key scientific problem for current agricultural system research.In this study,we selected wheat as our research target,and used long-time series statistical data,remote sensing images,and meteorological data as the main datasets to explore the dynamic characteristics,influence mechanism,and water resources responses of wheat spatial distribution.Main conclusions were drawn from this study as follows:(1)A comparative study on the dynamic characteristics of the spatial pattern of wheat,rice and maize in China.Based on long-term statistical data,we used the centroid model to evaluate the spatial pattern characteristics of wheat,rice and corn in China.Results showed that the planting centroids of rice and maize had a significant spatial movement from 1949 to 2014,while the planting centroids of wheat had no obvious migration pattern.Affected by human factors and natural conditions,the stable spatial distribution characteristics of wheat determine the stable distribution of wheat planting centroids in China.However,the difference in the direction and magnitude of the migration direction and magnitude of the wheat area and yield also reflects the spatial heterogeneity of the driving factors such as agricultural investment,field management and natural conditions in different regions.(2)Evaluations on the dynamic process and influence mechanism of the spatio-temporal pattern of wheat in China.Based on the statistical data of wheat area in China from 1949 to 2014,we calculated the centroids migration of winter wheat area and spring wheat area,and evaluated the driving factors of wheat area changes(as area changes lead to centroids movements)on the basis of socioeconomic data and meteorological data.Results showed that the centroids of winter wheat and spring wheat area changed significantly from 1949 to 2014.The major driving factor of winter wheat centroids movement was agricultural investment(i.e.,irrigated area),while the major driving factor of spring wheat centroids movement was the climate factor(i.e.,temperature).In addition,the scenario analysis in this chapter showed that among the climate factors considered in this article,temperature was the most important driving factor affecting the shift of the winter wheat area.(3)Assessment of the spatio-temporal pattern of winter wheat area in a representative region of China based on high-resolution images.Taking the Beijing-Tianjin-Hebei region,one of the main winter wheat producing regions in the North China Plain,as the study area,we evaluated the spatiotemporal pattern of winter wheat(the major wheat type in China)based on time series remote sensing images.Results showed that the spatial distribution of winter wheat in the Beijing-Tianjin-Hebei region has changed significantly from 1990 to 2019,showing a significant trend of "increasing in the south and decreasing in the north",with the hotspot areas of wheat planting moving significantly to the south.In terms of temporal change,the wheat planting area increased first and then decreased from 1990 to 2019,with the planting area reaching the maximum in 2000.In terms of spatial change,there were large sptiotemporal varitions across regions during the 30 years.The winter wheat area in high latitude has decreased significantly while that in low latitude has increased slightly,resulting in a significant southward movement of the wheat planting centroid.(4)The spatio-temporal impacts of winter wheat area changes on water resources utilization in Beijing-Tianjin-Hebei region.Combining the winter wheat distribution maps and time series meteorological data in the Beijing-Tianjin-Hebei region,we used the crop coefficient method and the Penman-Monteith methods to evaluate the impacts of the spatial distribution changes of winter wheat area on water utilization from 1990 to 2019.Results showed that the spatial distribution changes of winter wheat area reduced the water footprint of winter wheat production by 1.3 billion cubic meters in the Beijing-Tianjin-Hebei from 1990 to 2019.The water footprint of winter wheat production in high latitudes decreased significantly,while the water footprint of winter wheat production in low latitudes increased slightly,resulting in a southward movement of the water footprint centroid.The winter wheat area change in the study area was positively correlated with water footprint and blue water footprint,and the correlations in low latitude areas were significantly stronger than that in high latitude areas,indicating that winter wheat area changes in low latitude areas were more sensitive to the water utilization of wheat production.(5)Quantitative assessment of the effects of the winter wheat area changes on the groundwater table in Beijing-Tianjin-Hebei region.Based on the winter wheat distribution maps,water demand datasets,MODIS16 evapotranspiration products,and Grace gravity satellite data,we proposed a detection method to quantitatively assess the effects of winter wheat cultivation on groundwater table,and applied this method in the Beijing-Tianjin-Hebei region.The results showed that winter wheat cultivation had a lowering effect on the groundwater table in the Beijing-Tianjin-Hebei region,and this effect varied across different regions.From 2000 to 2019,the winter wheat areas with stable winter wheat distribution had a weaker effect on the groundwater table,while winter wheat cultivation in newly-added areas had an enhanced effect on the groundwater table.From 2000 to 2019,the areas where winter wheat cultivation had the most obvious effect on the groundwater table have shifted from regions with high water demand of wheat production to those with low water demand. |
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