Torrential rain is the definition of heavy rain. When
there is continuous rainfall and the amount is up to
130mm for one day, a special alert for torrential
rain will be issued; while if the amount is more than
50mm but less than 130mm and the rain may bring
disasters, an alert for heavy rain will be issued.
This catastrophe weather caused by heavy rain is most
frequent in May and June, the monsoon season. Or it
may also happen in rainy season in spring and autumn
with frontal surface or when the summer southward air
current is strong, leading to convective heavy rain or
torrential rain. The powerful airflow from the northeast
in direction caused by typhoon is also one of the reasons
for heavy rain or torrential rain.
Severe storm is a kind of catastrophic weather, which
always result in flood disasters and severe soil erosion
leading to a great number of economic loss like engineering
accidents, bursting of dikes, flooded crops and so on. For
some areas with low and closed terrain, the slow draining
of rainwater causes ponding in the field and over-saturation
of soil moisture and more geologic hazard ensued.