Flooding in the Indus River basin -A spatiotemporal analysis of precipitation records

摘要

Station and gridded precipitation data from ail over the Indus basin were analyzed for the periods 1951 to 2010 and 1986 to 2010. The non-parametric Mann-Kendall trend test was applied to determine whether statistically significant changes in precipitation amounts occurred over time, in due consideration of autocorrelation in the data. In addition, linear regression trend lines were fitted to the precipitation series by the method of least squares. We also investigated whether the precipitation in 2010, the year of a devastating flood, was the highest, second highest or third highest recorded annual and monsoonal total in the periods under observation. The use of gridded precipitation data unveiled a spatial pattern of precipitation trends in the Indus River basin. For the shorter time period, we found stronger evidence of positive trends in monsoonal precipitation time series compared to annual precipitation. Significant positive precipitation trends were primarily detected in the mountains: in the northwest (Hindu Kush and Sulaiman Mountains) and in the east (Himalayas) of the Upper Reaches of the Indus River. Negative precipitation trends, most of which are not significant, were detected in the northeast of the Upper Reaches (Karakorum and Transhimalaya) and in the lowlands. Compared to previous years, annual and especially monsoonal precipitation totals in 2010 were extremely high in the Himalayas, the Hindu Kush, the Sulaiman Mountains, and in the central lowlands. Strong monsoon precipitation in the arid high mountainous regions, not used to these amounts of precipitation, played a major role in the 2010 floods in Pakistan.