Climate extremes are commonly thought to be in association with rare weather events. To quantify how 'rare' an extreme weather event is, a small percentile (e.g., the 1st) or a large percentile (e.g., the 99th), defined against all weather samples, may be used for statistical analysis. In comparison, an extreme climate event is an average of weather conditions over a certain period that is 'rare' among all climate samples. In the analysis of changes in climate extremes, large percentiles such as the 99th, 95th and 90th or small ones such as the 1st, 5th and 10th may be applied as thresholds for quantifying extremes. If the value of a weather or climate variable exceeds the threshold, it is defined as an extreme. Sometimes, a certain fixed value is also used as a threshold, e.g., 50 mm/day of rainfall for extreme precipitation event and 35 °C of surface air temperature for extreme hot day for certain places (Zhai et al, 2003a). Some events such as droughts are more complex, as these can hardly be defined with a single meteorological variable.

Although extreme events happen with small probability, they have profound impact on society and environment (Karl et al., 1999) and often result in tremendous disasters. The types of climate extremes and related meteorological disasters affecting China are various, in association mainly with rain storm, flood, drought, heat wave, frost, sand storm, typhoon and heavy fog. In addition, climate extremes may induce secondary disasters. For example, heavy rainfall may lead to mudflow or landslide; high temperature and drought enhance chances of forest fires. There is a general spatial / seasonal pattern of climate extremes and disasters over the country. Dust storms occur most frequently in Northwest China in spring. Southeast China is typhoon-prone area with the active season from May to October. Among all the natural disasters, climate and meteorological disasters are the most frequent ones and their influences are enormous with a broad and far-reaching set of impacts. The major impacts are reflected in loss of life, illness, and adaptation costs in transportation, agriculture, energy and in frastructure. In China, about 750 km2 farm lands are hit by climate extremes and meteorological disasters such as droughts, floods and tropical cyclones, about 600 million people are affected each year. On average, the annual economic loss due to meteorological disasters in China is equivalent to 3-6% of Gross Domestic Product (GDP) and it has increased substantially from the 1980s to the 1990s and 2000s (Figure 8.1). Such increase is in association with both the development of social economy and changes in climate extremes.

The study of extreme weather and climate extremes in China has received increasing attention in recent years (Zhai et al., 2005a; Yan and Yang, 2000). This chapter is to introduce some results, especially on changes in temperature and precipitation extremes, tropical cyclones, droughts and dust-storms during recent 50 years.










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Fig. 8.1 Economic loss resulted from meteorological disasters in China during 1989-2005

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