Torrential rain comes into being in a rather complicated way,
Generally based upon the macrophysics, the main physical condition
for torrential rain is the a steady flow of adequate aqueous vapour,
strong and continuous upward movement of the air and the instability
of the atmospheric structure.
Good combination of weather systems in various size, underlying
surfaces and terrains may cause torrential rain. Main weather
systems that give rise to torrential rain in China are front,
cyclone, shear line, vortex, trough, typhoon, easterly wave,
Intertropical Convergence Zone and so on.
Besides, the thermal thunderstorms among arid and semiarid
areas can contribute to transitory torrential rain with small
Torrential rain often drops from cumulonimbus clouds. The
clouds need sufficient steam in the air and intense upward
movement pushing the steam up. When the water drops in the
clouds are more and more affected by this movement and can
not be hold by the rising airflow anymore, they will rapidly
drop onto the ground.
Other scientists suggest that the soil erosion along with the
destruction of forests is one of the most important reasons
for torrential rain. Because forest deterioration will increase
the amount of the water that flows out the catchment areas in
forest when raining.
There is also someone holding a view that the El Nino Phenomenon
and La Nina Phenomenon may cause abnormal weather with the result
of mass torrential rain.
El Nino is a warm current from north to south along the Coast
of Peru in South America after Christmas. Generally speaking,
it may bring torrential rain to the eastern tropical Pacific
Ocean, where there is not much rainfall at ordinary times. On
the contrary, decrease is seen on the rainfall in western
tropical Pacific Ocean, where it is supposed to be rainy
but when El Nino comes even drought can happen.
La Nina Phenomenon is what happens when the temperature of
eastern and middle surface of tropical Pacific Ocean drops
unusually and the trade wind intensifies. The eye-catching
torrential rain is attributed to the effects of the higher
temperature worldwide. Researches have pointed out that the
increasing average amount of vapour of earth caused by
global warming also contributes to the growth in the frequency
of intensified rain and the amount of low-pressured tropical