Magnification of flood disasters and its relation to regional precipitation and local human activities since the 1980s in Xinjiang, Northwestern China

Analyses of flood disasters were conducted using 1950-2001 data on the flood-damaged areas of cropland, the annual number of flood disasters and the direct economic losses in Xinjiang. There is an increasing trend in flood disasters in Xinjiang during the second half of the 20th century, especially since the mid-1980s. Results of a non-parametric Mann-Kendall test on the cropland-flooded index time series revealed an abrupt change in the mid-1980s. The reasons are discussed with respect to changes in annual precipitation and regional human activities, by correlating cropland-flooded area to annual precipitation and three socio-economic parameters (population, cropland area and GDP). The correlation coefficients between the flood-damaged area and the annual precipitation during the periods 1961-1998 and 1987-1998 were substantially higher than during the period of 1961-1986. The correlation coefficients between the flood-damaged area and the three human activity parameters, however, were relatively high for the whole period of 1961-1998, but generally not significant for the 1961-1986 and 1987-1998 periods, separately. These suggest that the occurrence of flood disasters could be mainly induced by local human activities before the mid-1980s, and thereafter mainly by abnormal precipitation in Xinjiang. Meteorological and hydrological records showed that the number of heavy rainfall events and the frequency of rainstorm flood disasters increased since the 1980s. In addition, siltation of reservoirs and loss of flood control structures are partly responsible for the increase of flood-damaged area. These results suggest that the increasing trend in flood disasters in Xinjiang since the middle 1980s could be attributed, at least in part, to an increasing trend in annual precipitation.