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Cloudburst
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The monsoon rains during July and August put a lot of water into the Himalayan soil but when you add to that mix cloudburst, well, you've got trouble.

Hi, I'm Bryan Yeaton and this is the Weather Notebook.

A cloudburst is a high intensity rainfall in a short period of time. As correspondent Manisha Aryal (Ma-Knee-shah Arr-ya'll) reports, scientists are finally beginning to pay attention to this little understood phenomenon.

A cloudburst occurs when a pregnant monsoon cloud drifts northwards, from the Bay of Bengal across the Ganges plains, then onto the Himalayas and bursts, bringing rainfall as high as 75 millimeters per hour.

Water engineer Ajaya Dixit is one of the few people researching the impact of monsoon cloudbursts on the environment and economy of the Himalayas. He says it's not clear yet what causes them.

During the monsoon period, this low pressure sometimes moves northwards over the mountains. The weather activity is very very intense and we get very very high intensity rainfall. This could be part of the larger meteorological process that has been going on historically. But to conclude scientifically, we really don't have the evidence to make precise judgment.

Even without a lot of data, says Dixit, planners and engineers have to start paying attention to cloudbursts.

When you begin to plan dams or reservoirs, it would be more prudent to begin to understand that these events do occur and to take care of the possibilities of the risks these events pose on hydraulic structures.

A 1993 cloudburst over the Kulekhani reservoir in Nepal, deposited huge amounts of silt on the reservoir and reduced its life by 87 years. That's correspondent Manisha Aryal of Kathmandu, Nepal. The Weather Notebook is a production of the Mount Washington Observatory, supported by the National Science Foundation.