Historical land use reconstruction for South Asia: Current understanding, challenges, and solutions

To deal with global warming and biodiversity loss, historical land use in South Asia received wide attention because of its huge population and rich biodiversity. We reviewed representative global and regional historical land use reconstructions for South Asia from their data sources, methods of area estimation and spatial mapping, and outcomes. Then we made some prospects on developing historical land use for South Asia. The land use area of South Asia in global reconstructions was mainly estimated using population. For the spatial pattern, most of them assumed that the historical distribution of land use in South Asia mimics satellite-based land use patterns or that the land use area was pixelized based on land suitability for cultivation and grazing. Large discrepancies exist among these global reconstructions in the land use area and spatial patterns with increasing magnitude with time in the past. The regional reconstructions of historical land use for South Asia used more regional historical records, but most covered only about one hundred years. The closer to the past, the lower the spatial-temporal resolution of these regional reconstructions. Great discrepancies also exist between these regional re-constructions because of the differences in cropland definition. Expansion of archaeological data sources, meta-analysis, and crowdsourcing will bring insights into area estimation of historical land use. Remote sensing and machine learning will facilitate spatial pattern mapping. Reconstruction region-by-region, and then integration, is also a solution for current challenges in reconstructing historical land use for South Asia.