SHANGHAI: They may not be as spectacular as the typhoons which batter China's southern coastal areas, but as the rain falls and temperatures rise, the impact of Shanghai's "plum rains" should not be underestimated.

Heralding the arrival of a stifling combination of heat and humidity, the romantically-named plum rains arrive in Shanghai in mid-June each year and are responsible for around a fifth of the municipality's yearly rainfall, coming down in less than a month.

But as the rains come down, the mercury rises, daytime temperatures nudge into the upper 30s and Shanghai's famous skyline vanishes into the murk as humidity climbs to more than 90 per cent.

"Every year we see increased cases of heat exhaustion and de-hydration, and because the weather is ideal for bacteria to grow, we see around twice as many food poisoning cases over the month than we would at other times of year," said a doctor surnamed Bai at Fudan University's medical centre, giving a clear example of why the period is also called the "mold rains."

"The weather can also make things worse for people with rheumatoid arthritis and respiratory diseases," she added.

According to a meteorologist surnamed Cao at the Shanghai Central Observatory, the rains, which get their name because they arrive at around the same time as plums become ripe, affect the Yangtze River and Huaihe River regions of China, with the band of rain stretching as far east as Japan.

The phenomenon is the result of the rain belt becoming caught between northward-moving warm air from the south of China and colder air currents from northern China and Siberia.

The rain lingers for around a month until the cold air recedes, allowing the warm air to spread north during July.

"Although too much rain can cause flooding, the arrival of the rains helps the growth of crops and re-stocks water supplies, and if the rains don't come there can be serious drought," said Cao.

Although most city dwellers are left sweating, sweltering and cursing the season, there is one group whose entrepreneurial spirit helps them make the most of it.

During the regular downpours umbrella sellers spring up on every street corner, hawking to those foolish enough to come out unprepared.

"This is the best time of year for umbrella sales," said a Mr Chen, who sells umbrellas in Shanghai's central Yangpu District.

"When it's hot people buy them for shade and when it's raining they get them to keep from getting wet.

"Sales double and, although I usually sell my umbrellas for 10 yuan (US$1.25), during the plum rains demand is higher so I can charge a bit more," he said.

Source: China Daily