Changes in precipitation extremes in alpine areas of the Chinese Tianshan Mountains, central Asia, 1961–2011

Based on the gridded and observed daily precipitation datasets from 1961 to 2011, changes in daily precipitation extremes in alpine areas of the Chinese Tianshan Mountains are discussed. Four indices that represent extreme precipitation events are selected and calculated. Maximum 5-day precipitation, simple daily intensity index and very wet day precipitation have increased significantly by 1.18 mm, 0.09 mm/d, and 6.75 mm per decade, respectively, while consecutive dry days have decreased at a rate of 5.83 days per decade during the study period. Changes in probability distribution functions of precipitation indices before and after the detected abrupt year also indicate a wetting trend. Generally, the linear trends of precipitation indices are spatially coherent. Approximately 79.0%, 83.8%, and 98.1% of the grid boxes show increasing trends for maximum 5-day precipitation, simple daily intensity index and very wet day precipitation, respectively, and the proportion of decreasing trends for consecutive dry days is 95.2%. Trends in most precipitation indices (except consecutive dry days) are highly correlated with total precipitation trends (p < 0.0001). Significant correlations between precipitation indices and Northern Hemisphere Annular Mode Index (also referred as Arctic Oscillation Index) in wintertime indicate that precipitation extremes in the study area are related to the Arctic Oscillation.