作为世界干旱气候研究动态及进展综述的续篇(Ⅱ),本文将进一步从纵向评述世界干旱气候在干旱指数、干旱区划分及分布、干旱气候变化、成因及预测等5核心内容的主要研究进展。要点如下: (1)各国先后共已提出了几十种有效的干旱指数;例如美国的Palmer干旱强度指数PDSI、标准化的降水指数SPI及卫星植被指数NDVI,特别是最前者,它们已在国内外获广泛应用。(2)当代划分干旱区时,已更多使用有效湿度判据P/PET;在近10种已有的世界干旱区划图中,以Meigs及Hulme and Marsh的图更接近实际,使用者更多;特别是后者。世界干旱半干旱区占全球陆地总面积的35%左右,可分北非、澳大利亚及中蒙等8大干旱区。(3)近千年(特别近百年)的全球气候变化是以全球气温一致变暖,降水气候则更多时、空间变化为主要特征的;近百年全球平均增暖了0.56~0.92 ℃;全球增暖主要归因于温室气体CO_2等排放量增加;过去60年全球干旱变化甚微;各干旱区的温、湿气候变化在年际/年代际尺度上常有增暖变干及增暖变湿两组合型。(4)世界干旱气候成因主要可分为热带海温及地形影响两大类,北非及中蒙干旱区分别是该两类的代表;全球海温(特别是热带各海区的暖海温)及土地的过度利用分别是南撒哈尔大旱的主要及次要成因;而青藏高原等地形及环流则分别是中蒙干旱形成的主要及次要成因。(5)干旱气候预测重点要抓年代际干旱的预测,其预测仍要走天气学、统计学及动力学延伸预测相结合之路。
英文摘要:
As the continued paper of the review (Ⅰ), the paper (Ⅱ) will further review the main progresses in world dryland climate, including drought indices, arid- and semiarid-zone dividing and their distribution, dryland climate changes, forming causes and projecting. The main points are as follows: (1) More than dozens availability drought "indices" have already put out in various countries, they are well-used in home and abroad. Say, the PDSI, SPI and NDVI indices and so on in the US. (2) Nowdays more researchers utilize the "moisture availability as the "criteria" in dividing the dry areas. Among nearly 10 existed arid- and semiarid-zone maps have been published, the map of Hulme and Marsh is more closer to the real world. On the average, the arid- and semiarid-area make totally up 35% of the global land area, they cover the 8 major arid areas: ie, the North Africa, Australia and China-Mongolia ones and so on; there are the home of about 20 billion people of the globe. (3) The global climate changes in past 1 000 (especially in the recent 100) years are mainly characterized by global warming of the surface air temperature and the larger temporal- and spatial-changes of precipitation climate. Due to the increased CO_2 and CH_4 greenhouse gasses, the global mean temperature increased 0.56~0.92 ℃ in the past 100 years. In contrast, beyond the East Asia and North Africa, the precipitation climate change links among other dry zones are not so close to each other. There are two combination partterns for temperature and precipitation change in various dry zone in the past. (4) There are many ways for the drought causes across the world arid zones. From the recent discussions about North Africa and China-Mongolia drought causes, it is seemely that the global arid climate forming may classified briefly in two types only: namely global tropical warm SST and mountain topography impact ones. North Africa and China-Mongolia arid areas are the respectively representation of the two types. The discussions show: for the former, it is caused by mainly the global warm SST, especially in the tropical zone and secondly by the land-air interaction; for the latter, by mainly the Qinghai-Xizang Plateau topography and secondly by the circulation. (5) The key point of the arid climate prediction is the one of the decodal drought. There are long road to go for the arid climate prediction.