Changes in Climate Regionalization Indices in China during 1961-2010

The regionalization of climate in China is based on a three-level classification in terms of lasting days for accumulated temperature (AT), aridity index, and July mean temperature. Based on daily meteorological observational data from 756 stations, trends and interdecadal variation in indices for classifying temperature zones, moisture regions and climatic sub-regions in the period 1961-2010 are discussed. Results reveal that the nationwide AT 10C (AT10) and its lasting days are basically increasing, while aridity in northern Xinjiang is decreasing. The increasing trend of July mean temperature in North China is found to be notably larger than in South China. In terms of their national averages, a marked step increase of AT10 and its lasting period, as well as July mean temperature occurred around 1997, while the aridity index presents no such clear change. By comparing regionalization areas for 1998-2010 with those for 1961-97, it is found that the semi-humid, semi-dry and dry regions in the sub-temperate zone, as well as the humid region in the middle subtropical zone, have experienced substantial shrinkage in terms of area. In contrast, the areas of semi-dry and dry regions in the warm temperate zone, as well as the humid region in the south subtropical zone, present drastically increasing trends. Owing to the influence of such step changes that took place in 1997, that particular point in time should be given close attention in future studies regarding the regionalization of climate in China.