The Question of Communist Land Degradation: New Evidence from Local Erosion and Basin-Wide Sediment Yield in Southwest China and Southeast Tibet

Abstract

Chinese Communist Party doctrine promotes the Confucian belief that the environment should be subjugated to man's will, and modern policies have been identified as compounding environmental degradation caused by historical agricultural practices. In this context, social scientists report massive increases in erosion throughout China, an assertion variously supported and questioned by daily sediment yield data in the Yellow and Yangtze River basins. In this study we used up to twenty-seven-year records of daily sediment yield for stations in southwest China and southeast Tibet to calculate annual and average annual sediment yields over the period of record. We also calculated coefficients for annual sediment rating curves as a way to determine interannual changes in sediment transport, that are insensitive to variations in rainfall. We found no systematic changes in annual sediment yield or rating curve parameters through time. Sediment yield is correlated with upstream area, mean annual rainfall, fraction of land under cultivation, population density, and mean monsoon rainfall but not with mean local relief, basin relief ratio, fraction of cropland from satellite data, or drainage density. Variability in mean annual sediment yield decreases as basin area increases, suggesting that larger basins store sediment more effectively and buffer against extreme events. We propose that anthropogenic changes to sediment yields have been smaller than the magnitude of interannual variability and might be comparable to the effect of the regional rainfall gradient across the basins. In basins with substantial anthropogenic activity, sediment storage might be affecting any signal we might otherwise see.