清代中期苏皖地区耕地数据网格化处理及精度对比

格点化区域历史土地利用数据是进行历史土地利用/土地覆被变化环境效应模拟的基础。本文基于苏皖地区耕地垦殖倾向,分别采用清代中期苏皖地区省域及县域耕地数据进行网格化降尺度处理,分配至10 km×10 km的网格中,并将两种分配结果进行对比评估来定量探讨数据的空间范围大小对格点化数据的精度影响。得到以下结果:①用苏皖省域耕地数据和县域耕地数据模拟的网格化结果之间存在差异,平均差异率为16.61%。相对差异率较小(-10%~10%)的网格有24.55%,较大(>70%或<-70%)的网格有13.3%,主要存在于洪泽湖流域及苏北北部沿江平原(黄河改道前入海口处)。②苏皖地区清代中期耕地的空间分布具有一定的地域差异。耕地垦殖率较高的地区主要集中于苏南平原地区的太仓市和昆山市北部,苏皖西北部的砀山县、丰县和沛县,垦殖率均在80%以上;而苏北北部旧黄河入海口、洪泽湖流域、太湖流域及安徽南部山区丘陵地区垦殖率较低,多在10%左右。③1735 年耕地主要分布于海拔高度≤100 m,坡度≤2°的地区。到1980s 时,不同坡度下的垦殖率有较大增加。

Rasterizing cropland data and accuracy comparison in Jiangsu and Anhui Provinces in the Mid-Qing Dynasty

Historical grid data of land use are the basis for environmental effect simulation of land use/land cover change. This study distributed the cropland data for the mid-Qing Dynasty in Jiangsu and Anhui Provinces into grid cells with a spatial resolution of 10 km×10 km by using the provincial-level and county-level cropland data. It also compared and assessed the two distribution results to examine the accuracy of the downscaling and rasterization of statistical data at different spatial scales. The results are as follows: (1) The distribution result that used the county-level data has higher precision. (2) There exist differences between the provincial and county statistical data downscaling results, and the average difference is 16.61%. For 24.55% of the grid cells the difference is between -10% to 10%; 13.3% of the grid cells have a difference of above 70% or below -70% and these cells are mainly in the Hongze Lake basin and the northern plain of Jiangsu Province (the estuary before the Yellow River diversion). To reduce the distribution error and improve the downscaling precision, it is necessary to reconstruct historical cropland distribution using county data. (3) The reconstructed cropland distribution in the mid-Qing Dynasty in Jiangsu and Anhui Provinces reveals some regional differences. The highly farmed area was mainly concentrated in Taicang and Kunshan in the central eastern coastal plain region, and in Dangshan, Feng, and Pei Counties the reclamation rates were above 80%, with the highest in Dangshan at 89.8%. But the reclamation rate in the estuary of the old Yellow River course in the north of Jiangsu, the Hongze Lake basin, the Tai Lake basin, and the southern Anhui mountainous and hilly region was very low, at around 10%. (4) In terms of altitude and slope, in 1735, the cropland was mainly distributed in places where the altitude is lower than 100 m and slope lower than 2°. In the 1980s, however, the reclamation rate had greatly increased in areas with various slopes—for example, the reclamation rate under 2° slope increased from 45.29% in 1735 to 74.21% in the 1980s.