Interdecadal Changes in Heavy Rainfall in China during the Northern Summer

Abstract

Using ground observations of daily rainfall over China during summer (June - August) for the period 1961 - 95, we examined interdecadal changes in the distribution of rainy events as a function of the rain rate and assessed their contributions to the total summer rainfall. We found that central China was wetter, and northern and southern China were drier in the decades following 1979 as compared to the earlier decades. The interdecadal changes in the Chinese summer rainfall are closely linked to those in large-scale circulations: the southward displacement of a westerly wind at the levels of 200 and 850 hPa over East Asia and an enhanced 850 hPa northerly wind over central-eastern China. The corresponding 850 hPa relative vorticity increased (decreased) over central (northern and southern) China where the summer rainfall has increased (decreased) during the later decades. Interestingly, the change in the total number of rainy events was found to be negligible during the entire period of data collection. Across the overall region (mostly eastern China), a large amount of interdecadal changes is accounted for by less than 20% of the total number of rainy events in the heavy-to-extremely-heavy categories (≥ ~25 mm day-1). The possible causes-associated with large-scale circulations-and the implications of the present results are discussed.

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