Just as water is fundamental to life, precipitation is integral to society and ecosystems. However, heavy rain is one of the most frequent and widespread severe weather hazards to affect China. Heavy Rain is defined as rainfall greater than or equal to 50 mm in past 24 hours.

In China, heavy rain is relatively common. Often, a significant amount of precipitation occurs in only a few hours, leading to severe flooding and landslide risk.

Causes of Heavy Rain

Rain occurs when the water vapor "held" in warm, moist air condenses into liquid water and falls. The primary difference between light rain and heavy rain is the amount of moisture that is present in the air mass, which is proportional to the size of the air mass. For heavy rain, the amount of moisture in the air mass must be disproportionately large compared to its size. There are several weather events where this is typical, such as in cold fronts, tropical storms, hurricanes, and monsoons. Rainy weather patterns like El Niño and the Pacific coast's "Pineapple Express" are also moisture trains. Global warming, too, is thought to contribute to heavier precipitation events, since in a warmer world, the air will be able to hold more moisture to feed soaking rains.

Potential consequences of heavy rainfall

Heavy rainfall can lead to numerous hazards, for example:

  Runoff: If heavy rains arrive more quickly than the ground can absorb water, you get runoff--stormwater that "runs off" the land instead of seeping into the ground. Runoff can carry pollutants (like pesticides, oil, and yard waste) into nearby creeks, rivers, and lakes.

  Flooding & flash flooding: If enough rain falls into rivers and other bodies of water it can cause their water levels to rise and overflow onto normally dry land. The hazards includes risk to human life, damage to buildings and infrastructure, and loss of crops and livestock

  Mudslides: If rain is record-breaking (typically more rain in a few days than is normal over a month or year) the ground and soil can liquify and carry unsecured objects, people, and even buildings away in debris flows. This is exacerbated along hillsides and slopes since the ground there is more easily eroded away. Here in the U.S., mudslides are common in Southern California. They're also common in Europe and Asia, especially India, Bangladesh, and Pakistan where they often lead to death tolls in the thousands.

  Landslides, which can threaten human life, disrupt transport and communications, and cause damage to buildings and infrastructure.

Where heavy rainfall occurs with high winds, risk to forestry crops is high.