Project optimization for high-standard farmland upgrading using TOPSIS and coupling coordination degree

67 million hectares of high-standard farmland has been constructed in China by the end of 2022. The production quality and capacity of these farmland need to be upgraded after long-time utilization, low investment, and disaster damage. The next construction is required for the food security. However, there is seldom report so far. This study aims to optimize the projects and then upgrade the high-standard farmland using TOPSIS and coupling coordination degree. Taking the Laoling City, Shandong Province as the research area, 87.93% of field was built into the high-standard farmland from 2013 to 2022. The evaluation index system was constructed from three aspects: construction foundation, fertility quality and water resource utilization. 14 indicators were contained, such as farmland area, building time, cost input, road accessibility, field breakage degree, soil organic matter, soil P, soil K, salinity degree, soil texture, water quantity, pond density, ditch density and water system connectivity. Furthermore, 57 688.44 hm² high-standard farmland from 950 administrative villages were taken as the evaluation unit to realize the implicative construction. The AHP (analytic hierachy process) and TOPSIS (technique for order preference by similarity to ideal solution) analysis were chosen to evaluate the current situation as functional effectiveness of facilities, potential to arable land productivity and sustainable utilization of water resources. The production capacity of farmland was also evaluated to determine the coupling coordination degree for the cooperativity among three aspects. The upgrading project areas were delimited using the cooperativity index and spatial patterns. The results show that: 1) The construction foundation was relatively superior in the southwest and eastern regions, while the weak performance distributed mainly in the south and central regions. High fertility areas were accounted for a small proportion of 14.46% in the central, southern and northeast regions. Water resources presented a trend of high in the central region and low in the northern and southern regions. 2) The coupling coordination index of the three dimensions were ranged from 0.41 to 0.85. The high values were clustered in the southwest, east and northeast, whereas, the low values were in the south and northwest, and the median cross-distributed in the central and southern regions. 3) According to the coupling coordination degree index, the information and pertinency target, the evaluation units were broadly classified as near-term, mid-term and long-term construction sequences, where the areas of each period were 8 633.23, 11 004.64 and 9 102.62 hm², respectively. According to spatial pattern, three sequences were divided into 12 upgrading projects with the average stage of 4 projects. Different obstruction factors were optimized to improve the quality and efficiency of each project, in term of water source security, facilities, fund integration, land capacity and structural improvement. The construction quality and operation period of high-standard farmland were considered to balance the land use with productivity degradation. The optimal configuration was achieved under the constraint of water resources, following the principle of coordination and adaptation to local conditions. Thus the finding can also provide a strong reference to select the priority areas for the high-standard farmland.