CRYPTIC LEGACY OF CHINESE COMMUNIST PARTY ENVIRONMENTAL POLICIES ON SEDIMENT YIELD IN SW CHINA AND SE TIBET

Chinese Communist Party doctrine promotes the Confucian belief that the environment should be subjugated to man’s will, and modern communist policies have been identified as compounding environmental degradation caused by historical agricultural practices pre-dating the communist revolution. In this context, social scientists report massive increases in erosion throughout the country, an assertion variously supported and questioned by daily sediment yield data, collected for up to 20 years, in the Yellow and Yangtze River basins. We use 1 to 27 year records of daily sediment yield for stations in southwest China and Tibet to calculate annual and average annual sediment yields over the period of record. We also calculate coefficients for annual sediment rating curves as a way to measure inter-annual changes which are insensitive to variation in rainfall. We find no systematic changes through time. There is a weak correlation between sediment yield and rainfall (r² = 0.27) and fraction of land under cultivation (from coarse-scale county government data; r² = 0.22), but no correlation between sediment yield and population density, land use, % cropland (from satellite data) or mean local relief. In addition, variability in mean annual sediment yield decreases as basins increase in area, suggesting that larger basins more effectively store sediment and buffer against extreme events. We propose that these results imply that basin-scale anthropogenic changes to sediment yields have been smaller than the magnitude of inter-annual variability, although they may be comparable to the effect of the regional rainfall gradient across the basins. In basins where there has been substantial anthropogenic activity, small scale sediment storage may be affecting any signal we may otherwise see. These results suggest that future research on anthropogenic controls to sediment yield should focus on basins smaller than about 5,000 km².