Uncertainties of global historical land use scenarios in past-millennium cropland reconstruction in China

摘要

Global historical land use scenarios, including HYDE3.2 and PJ, are widely used in global change research. However, their uncertainties have not been well evaluated. Based on the historical-documents-based Chinese historical cropland dataset (CHCD), we evaluated the uncertainties of the representative global historical land use scenarios in past-millennium cropland reconstruction in China in terms of the area and spatial pattern. The results show that apparent differences exist in cropland area at the national scale between HYDE3.2 or PJ and CHCD for the Song-Liao-Jin Era (AD 1000-1279) and the Qing dynasty to present (AD 1644-1999), with a maximum relative difference ratio (RDR) of about-35 and 112, respectively. We detected similar differences at the provincial scale, except for Guizhou, Heilongjiang, Jilin, and Xinjiang provinces. Specifically, HYDE3.2 underestimates cropland areas of nine provinces, with an absolute difference of up to 5.2 x 104 km2, while overestimates cropland areas of ten provinces, with an absolute difference of up to 5.1 x 104 km2. As for the spatial pattern, the percentage of grids with an absolute value of RDR greater than 70 between HYDE3.2 and CHCD reach up to 54-82, mainly distributed in major agricultural areas, frontier areas, and geographical transition zones. In conclusion, neither HYDE3.2 nor PJ reflects China's cropland area and its past-millennium change accurately, resulting from the differences in data sources, area estimation, and spatial allocation methods.