Changes In Climate Regionalization In China Under The Background Of Climate Warming

The regionalization of climate in China is based on a three-level classification in termsof lasting days for accumulated temperature (AT), aridity index, and July mean temperature.Based on daily meteorological observational data from756stations, trends and interdecadalvariation in indices for classifying temperature zones, moisture regions and climaticsub-regions in the period1961~2010are discussed. Thus the dividing line for climateregionalization, around1997, is proposed. Secondly, comparison between the regionalizationpatterns before and after1997is studied. Additionally, the stability of the indices in theperiod of1998~2010is discussed. Finally, the reasons causing the interdecadal variability ofthermal indices are probed into. Results are listed as follows.The nationwide AT≥10°C (AT10) and its lasting days are basically increasing, whilearidity in northern Xinjiang is decreasing, indicating that the degree of drought is weaker. Theincreasing trend of July mean temperature in North China is found to be notably larger thanin South China. In terms of their national averages, a marked step increase of AT10and itslasting period, as well as July mean temperature occurred around1997, while the aridityindex presents no such clear change except for the northern Xinjiang. Hence,1997can betaken as the dividing line for regionalization in China.Boundaries for the regionalization indices have experienced more or less movementsafter1997. In terms of the boundaries for the temperature zones, northward movements,especially for the middle subtropical zone, is found in East China. The movements inNorthwest China are less obvious. Compared with the temperature zones, the movements ofthe boundaries for the moisture regions are weaker. It should be noted that the boundaries tothe east of110°E exhibit more apparent movements. Furthermore, the boundaries for theclimatic sub-regions have experienced northward movements as well. By comparingregionalization areas for1998~2010with those for1961~97, 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 middlesubtropical zone, have experienced substantial shrinkage in terms of area. In contrast, theareas of semi-dry and dry regions in the warm temperate zone, as well as the humid region inthe south subtropical zone, present drastically increasing trends. Spatial differences of thestability of the regionalization indices are revealed. For the lasting days of the AT10, the poorstability is found in the northeast of Inner Mongolia, the north of Heilongjiang Province and the east border of Tibet Plateau. In contrast, the indices in Hainan Province and the south ofYunnan Province are the most stable. For the aridity, the drier the place is, the less stable theindices present. For the July mean temperature, it is found that the indices are more stable inthe regions with higher temperature. Generally, the stability of the indices for the climaticsub-regions, the temperature zones and the moisture regions are respectively the best, secondand the poorest.In most parts of China, the mean temperature in spring, summer and autumn is generallyabove10℃. A marked step increase of mean temperature in spring, summer and autumnoccurred in mid-to-late1990s. Furthermore, the warming in spring and autumn is moreobvious than that in summer. Over the most parts of China, the200hPa geopotential height,the500hPa geopotential height and the sea level pressure during1998~2010is higher thanthat during1961~1997, which is conductive to the warming over China. Similarly, distinctchanges of the Arctic sea ice density, the Antarctic sea ice density, the sea surface temperatureover equatorial Pacific and North Atlantic during spring, summer and autumn are discoveredin mid-to-late1990s. The difference is that for the Antarctic sea ice density as well as the seasurface temperature over equatorial Pacific and North Atlantic, their interdecadal variabilitycauses the adjustment of the atmospheric circulation, however, for the Arctic sea ice density,its interdecadal variability is caused by the changes of the atmospheric circulation, which issame as the mean temperature in China. Therefore, it is deduced that the Antarctic sea icedensity as well as the sea surface temperature over equatorial Pacific and North Atlantic actedimportant roles in the warming of China since1997.