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Plum Rains

This is weather peculiar to the eastern regions with latitudes of 28°-33°N., which roughly comprise the Middle-Lower Changjiang River (Yangtze River) valley, the southern Huaihe valley, Zhejiang and Fujian provinces. They come every year between late spring and early summer, approximately at the time that plums ripen. The rains last for about a month. They are also called “mold rains” because the duration of the rains create conditions which are ideal for mold development.

Although the timing varies from year to year and from place to place, plum rains generally begin in mid-June and end in mid-July. Because the rains coincide with rice-transplanting time, the rainfall is favorable to the growth of rice although excess rain can result in water-logging.

Plum rains linger into mid-July due to weather conditions north and south of the Yangtze River and Huaihe river valleys. Around this time, monsoons in the southeast monsoon have gathered force and drive warm, moist air currents towards the Yangtze River and Huaihe river valleys. The monsoons, however, cannot blow the currents any further north. Similarly, the cold air current which is pushed down from the north is not strong enough to travel any further south. Thus, when the two currents meet in the Yangtze River and Huaihe river valleys, neither is strong enough to drive the other out. This causes the rain belt to linger and consequently gives rise to intermittent drizzles until early or mid-July, when the warm current prevails over the cold current and drives it back to north China.

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