A spatially explicit reconstruction of cropland based on expansion of polders in the Dongting Plain in China during 1750–1985

Global historical cropland datasets allocate cropland areas into grids above on the assumption that land suitable for crops is similar to that in the present or changeless over time. However, land suitability has changed over time. The Dongting Plain, which is full of polders, is characterized by changing land suitability for crops over the past 300 years and provides a case study of the impact of changing land suitability on spatially explicit reconstructions. Here, cropland areas were reconstructed at the county level and allocated into grids at 0.5′ × 0.5′. This allocation was based on the expansion of polders, which indicated land suitable for crops. The results showed the following: (1) The land suitable for crops constituted 68.24% of the total area in 1750 and it expanded after 1850, which in 1911, 1949, and 1985 was 1.10, 1.18, and 1.25 times that of 1750, respectively. (2) The regional cropland area fraction was 21.60% in 1750 and it increased after 1850, which in 1911, 1949, and 1985 was 127.21%, 140.27%, and 156.03% that of 1750. (3) The grids with cropland fractions increased due to polder development by more than 30% in the middle of the region from 1750 to 1985, occupying 32.16% of the total grids. (4) Changes in the land suitability for crops impacted the spatially explicit reconstruction. The grids unsuitable for crops were 78, 46, and 28 in 1850, 1911, and 1949 at 0.5′ × 0.5′, which constituted 19.21%, 11.33%, and 6.90% of the total grids, respectively. In comparison with this study, some of the grids unsuitable for crops were allocated as cropland by HYDE 3.2 and covered 93.59%, 89.13%, and 82.14% of the total unsuitable girds.