W Ghats influences Karnataka rain: IISc study

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W Ghats influences Karnataka rain: IISc study

Two Bengaluru researches have attributed the monsoon rainfall magnitude in Karnataka and Maharashtra to the topography of the Western Ghats, which they claim is responsible for bringing showers to the two states as compared to others in the region.

The researchers claim that the mountainous barriers of the Ghats are one of the major contributing factors to heavy rainfall, which occurs mostly during June and July, and that weather department predictions are off the mark as this is not taken into account. Using rainfall data for the last 14 years, the duo from the Indian Institute of Science (IISc), Bangalore, and Indian Institute of Remote Sensing, Dehradun, found three heavy rainfall spots in Maharashtra and two in Karnataka, but found no such spots in Kerala or Tamil Nadu.

When strong wind hits a mountain barrier, an upward draft is created to takes the clouds to a specific height over the Western Ghats, leading to rainfall. In the summer months between March and May, the Western Ghats heat up and attract large quantities of moisture-laden air from the sea, leading to higher rainfall in June and July. After the rain, the temperature difference is reduced and large cloud formation is slowed down.

“Since the Western Ghats is perpendicular to the monsoon winds, the impacts are clearly visible here. This cannot be extended to the Himalayas,” Sayli Tawde from the IISc, one of the coauthors of the study, told Deccan Herald.

The rain was more on the “windward” side of cascaded mountains — the side of mountain ranges that are exposed to monsoon winds. This is because, the barrier created by a cascaded mountain range restricts flow of clouds for a longer time, thus giving more time for rain formation.

If the barrier is small, like an isolated mountain as in Kerala, water droplets are carried away to the other side of the mountain and rain on the windward side is less. Though overall rainfall was observed in Karnataka due to the presence of a cascade mountain range, the highest rainfall site is Ratnagiri in Maharashtra. The two scientists, however, could not find out the reason why Ratnagiri gets more rain. The research has appeared in the online edition of the International Journal of Climatology.

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