Spatial pattern evolution of dryland-to-paddy conversion in China and its adaptive management from the year 2000 to 2020

Irrigation agriculture has become integral to global food production because it drastically improves productivity. In the past 20 years, driven by food demand and policy guidance, China has carried out large-scale cropland improvement projects on the land consolidation of dryland-to-paddy conversion (LC-DtPC). However, the unclear spatial pattern and the suitability of LC-DtPC have limited the adaptive management of LC-DtPC and the scientific protection and sustainable utilization of arable land. Therefore, this study used 30 m×30 m remote sensing data for five periods from 2000 to 2020 to reveal the spatial pattern of LC-DtPC of cropland in China and its conversion characteristics and then constructed a suitability evaluation system of LC-DtPC by selecting 11 indexes from four dimensions, namely, topography, climate, soil, and tillage, to assess the spatial matching effect of LC-DtPC project implementation and explore adaptive management zoning and strategies. The results showed that the area of LC-DtPC in China from 2000 to 2020 amounted to 1 297.04×10⁴ hm², accounting for 7.31% of the total cultivated land. The LC-DtPC was mainly concentrated in the Sanjiang Plain, Jianghan Plain, Central Henan Province, East of Sichuan Province, and Central Jiangsu Province. There was a large increase in the LC-DtPC area in 2005-2010 and 2015-2020. In general, the suitability of the implementation of LC-DtPC in the drylands of China was not favorable. Among them, 5.14%, 10.49%, 17.34%, 30.66%, and 36.37% of the national dryland area was suitable, more suitable, generally suitable, barely suitable, and unsuitable, respectively. In terms of spatial perspective, the suitability of LC-DtPC was better in Southeast China and Northeast China. Among them, terrain and irrigation water sources were the main influencing factors. Then, the raster superposition analysis was used to overlay the results of the LC-DtPC with the suitability evaluation to analyze the effect of spatial matching for the implementation of LC-DtPC. Through the spatial matching statistics, it found that the overall effect of LC-DtPC in China from 2000 to 2020 was unsatisfactory. The areas of LC-DtPC that were fully matched, more matched, generally matched, barely matched and unmatched were 88.13×10⁴, 373.13×10⁴, 456.43×10⁴, 229.62×10⁴ and 149.71×10⁴ hm², respectively, and their percentages were 6.80%, 28.77%, 35.19%, 17.70% and 11.54%, respectively. Therefore, adaptive management of LC-DtPC was important. This study attempted to analyze the mechanism of adaptive management of LC-DtPC and proposed a hierarchical zoning management method for LC-DtPC to guide the implementation and management of LC-DtPC. In the future, government departments can divide different adaptive management zones for LC-DtPC based on suitability priority levels, such as priority remediation zones, key adjustment zones, reserve restriction zones, and orderly withdrawal zones. At the same time, according to the regional characteristics, the government can formulate differentiated LC-DtPC management strategies from planning, implementation, evaluation, and monitoring. This study can provide a scientific basis for arable land protection, ecological protection, and restoration planning of national land space, and the delineation of the two zones.