Precipitation has "exceeded the standard" and heavy rain and torrential rain will soon hit these areas

Ask AI · How will future heavy rains intensify the risk of secondary disasters?

In recent days, many areas in southern China have experienced frequent overcast and rainy weather, with precipitation significantly above average, and locally, rainfall intensity has been unusually strong for the same period. As the active period for severe convective weather approaches, the next two rounds of rainfall will be stronger and more intense, with convective characteristics becoming even more pronounced; meanwhile, because the heavy-rainfall areas overlap, it is necessary to remain on alert for various types of secondary disasters that may be triggered.

Since March 15, precipitation in the northern and central parts as well as the western part of Hunan, the northern part of Jiangxi, the southern part of Hubei, and the central and eastern parts of Guizhou has been 30%–80% higher than in the same period in previous years. In places such as northern Hunan and eastern Guizhou, some areas have seen rainfall amounts that are more than double. For example, in Changsha, there have already been 21 rainy days since March—this does not even include cloudy days, and the time when the sun actually shows is very limited.

Over the next 7 days, Jiangnan, northern South China, the eastern part of the Sichuan Basin, and areas in Guizhou will continue to experience overcast and rainy weather. Rainy days may reach 5–7 days, and in most areas, total accumulated precipitation will remain significantly above average for the same period. There are two main rainfall periods—March 29–31 and April 2–4.

The coming round starting tomorrow will bring even stronger rainfall. From March 29 to 31, some areas in Chongqing, eastern Guizhou, northern and southwestern Hunan, southwestern and central-western Jiangxi, northern Guangxi, northern Guangdong, and central-western Fujian will experience heavy rain or thunderstorms, and in some areas—such as southwestern Hunan and central Jiangxi—there will be very heavy rain!

The centers of heavy rainfall are relatively scattered, but local rainfall intensity is strong. Cumulative rainfall will be 30–60 millimeters, with some areas reaching 100–150 millimeters, and locally exceeding 180 millimeters.

Severe convective weather will also be more prominent. Jiangnan, the central and northern parts of South China, and areas such as Guizhou—starting from north then moving south—will experience the first large-scale mixed-type strong convective weather process this year.

Some areas in central-southern Guizhou, southern Hunan, central-southern Jiangxi, western Fujian, northern Guangxi, and Guangdong will see thunderstorm gale winds of 8–10, with hail occurring locally. In Hunan and Jiangxi, the maximum thunderstorm gale wind speeds can reach level 11. In Guizhou, the central-southern part of Hunan, Jiangxi, Fujian, northern Guangxi, and northern Guangdong, the maximum hourly rainfall will be 20–50 millimeters, and locally it may exceed 60 millimeters.

Experts say that the evening of the 29th to the 30th will be the strongest period for rainfall in this round, with the rain area shifting somewhat southward on the 31st. Rainfall will pause in some areas on April 1, but from April 2 onward, rainfall will strengthen again.

Looking ahead to the later period, from April 2 to 4, Jiangnan, northern South China, and areas such as Guizhou will see moderate to heavy rain, with localized areas experiencing thunderstorms or very heavy rain.

In recent days, sustained overcast and rainy weather in Jiangnan and Guizhou has already pushed precipitation “beyond the limit.” In the next few days, however, the rainfall areas in Hunan, Jiangxi, Guizhou, and other places overlap to a higher degree with the regions that already had above-average rainfall earlier. With soil moisture already relatively high, it is important to guard against disasters such as flash floods, mudslides, and landslides that may be caused by continued rainfall and localized heavy downpours, and to guard against the adverse impacts of rainfall on transportation, urban operations, and other activities.

The appearance of this year’s first large-scale strong convective weather also means that southern China has entered a period when severe convective weather occurs frequently. In the next two rounds, it is necessary to stay alert for strong convective weather phenomena such as short-duration intense rainfall.

From a meteorological perspective, rainfall of 20 millimeters or more within 1 hour is generally defined as short-duration intense rainfall. It is characterized by strong locality, sudden onset, high precipitation intensity, and concentrated duration. Compared with ordinary heavy rain, it carries greater potential danger.

Because the intensity of short-duration heavy rainfall is high and the timing is concentrated, it can increase the load on drainage systems, quickly lead to urban waterlogging and farmland waterlogging, and may also trigger secondary disasters such as flash floods, mudslides, and collapses.