Spatial-temporal variability characteristics of precipitation structure across the upper Yangtze River basin, China

Daily precipitation data covering 1961—2005 from 67 meteorological stations across the upper Yangtze River basin are used to analyze spatial-temporal variability characteristics of precipitation structure in the context of climate change and human activities. The autocorrelation component in precipitation time series is eliminated by the Trend Free Pre-Whitening method, while the variability and trend in the precipitation structure are detected by the nonparametric Mann-Kendall method. Results show that over the upper Yangtze River basin and its sub-basins, the incidence rate of precipitation events for different durations decreases exponentially with the increase of precipitation durations; while, the corresponding contribution rate is found to be first increasing and then decreasing, with predominantly by short-duration precipitation events. It is detected that the year of 1976 was marked by an abrupt change for the contribution rate of short-duration (1 d and 2 d) precipitation events; while, the timing of abrupt changes for incidence rate and contribution rate of the precipitation events with long-durations of 6 and 10 days was in 1984 and in 1999 respectively. An upward trend is detected in the number of consecutive occurrences of short-duration precipitation events, with higher precipitation intensity and contributing to larger portion of total precipitation amount; while, the opposite is true for long-duration precipitation events. Tests are all significant for both above characteristics of precipitation structure amongst the Min River basin and the Dadu River basin, which are the sub-basins of the upper Yangtze River basin, as well as its main course areas.