Climatic Jumps in Precipitation and Extremes in Drying North China during 1954-2006

Changes in precipitation and its extremes in China were analyzed based on daily precipitation series from 1954 to 2006 at 740 stations. Indices of absolute extremes (e.g., heavy rains over 25 mm day(-1)), relative ones (e.g., events exceeding the 95th percentile for local sites and given time in a year), and parameters of fitted Generalized Extremes Value (GEV) distributions were investigated. Many of the precipitation and index series exhibited climatic jumps during the 1960s, around 1980 and in the 1990s. In particular, the widely-concerned drying process in North China was essentially formed by three drying jumps, indicating a stepwise weakening or southward retreating process of the East Asian summer monsoons during the second half of the 20th century. Changes in the atmospheric circulation in association with the regional drying jump around 1980 were analyzed based on the ECMWF 40 Years Re-Analysis (ERA-40) data available from 1958 to 2002. A significant phase shift was found in summer circulation indices and the northwestern Pacific Subtropical High during the late 1970s and the early 1980s. The drying jumps also led to abnormal variability in extreme rainfall events in the region, indicating that extreme events with higher intensity could happen in some years during recent decades than earlier, despite a decrease in the long-term mean precipitation.