Mapping Center Pivot Irrigation Systems In Global Arid Regions And Analyzing Their Spatial Relationship With Freshwater Resources

Ensuring freshwater availability and supply sufficient for socio-economic development is important for human health and productivity.Globally,increasing industrial agriculture is driving crop productivity,with increasing surface water and groundwater being withdrawn for irrigation.Center pivot irrigation systems(CPIS)are irrigation systems that irrigate farmland by means of a rotating spray arm supported by a central pivot.It is a highly efficient method of irrigating large farmland,distributing water evenly and increasing crop yields.The analysis of central pivot irrigated farmland can be used as a representative of agricultural modernization in arid and semi-arid regions,and it can determine the trend of agricultural modernization in arid and semi-arid regions and the relationship between agricultural modernization and water resources.It also helps governments to better understand the current status of freshwater stress and ecosystem sustainability associated with agricultural intensification in arid and semi-arid regions,to better judge the environmental consequences of agricultural modernization,and to formulate sustainable water management strategies.Therefore,remote sensing mapping and water resources analysis of central pivot irrigated farmlands in arid and semi-arid regions of the world are very important and necessary.In this thesis,based on the instance segmentation algorithm Cascade Mask R-CNN,the backbone network ResNet is replaced by ResNeXt with group convolution module and the convolutional attention module is added to each layer,and Point Rend is added to the Mask Head so that the network can obtain better improvement of the target edge accuracy and precision during segmentation.Later,the improved instance segmentation network is used to map the distribution of central pivot irrigated farmland in the global arid and semi-arid regions in 2021 and 2000 using Sentinel-2 and Landsat-7 remote sensing satellite data.Geospatial analysis methods were used to derive the relationships between CPIS and freshwater resources.Overall there were about 10.26 million hectares(Mha)of irrigated areas equipped with CPIS in global arid areas in 2021,and there were a total of 4.41 Mha of central pivot irrigated farmland added in the past twenty years at a relative increase of 75% compared with those at the beginning of this century.Although North America increased the largest total area of centrally pivoted irrigated farmland,the other five continents had higher relative increases,with Africa having the highest relative growth of 253%.The analysis of spatial relationships between central pivot irrigated farmlandand freshwater resources indicates that the stress on freshwater resources from industrial agriculture is intensifying in arid areas globally.Overall,the world’s arid regions with the highest water stress from central pivot irrigated farmland are mostly located in western North America,northern Africa,and the Arabian Peninsula.