Western Ghats and Orographic Rainfall

The Western Ghats act as a major orographic barrier to moisture-laden winds reaching India’s west coast. By forcing the Arabian Sea branch of the southwest monsoon to rise, they produce heavy windward rainfall and a marked rain-shadow region over the interior Deccan Plateau.

Mechanism of orographic rainfall

The Western Ghats run roughly parallel to the west coast and intercept the Arabian Sea branch of the monsoon. Moist air ascends their western slopes, expands and cools, leading to condensation and orographic rainfall. After crossing the crest, the air descends, warms and becomes relatively drier.

Resulting rainfall pattern

• The windward western slopes and adjoining Konkan, Goa, coastal Karnataka and Kerala receive heavy southwest monsoon rainfall.
• Rainfall decreases sharply east of the crest, creating the Deccan rain shadow over interior Maharashtra, Karnataka and adjoining areas.
• Relief, elevation, slope orientation and gaps in the Ghats create local variations in rainfall and permit some moisture to penetrate inland.
• The Ghats do not determine the entire rainfall pattern: the Bay of Bengal branch, convection and retreating monsoon also supply rain to peninsular India, especially the Tamil Nadu coast.

Environmental significance

This rainfall contrast helps sustain wet forests on the western side and comparatively drier ecosystems inland. Intense rainfall on steep slopes also produces rapid runoff, erosion and landslide susceptibility, while the Ghats form headwaters for many west-flowing and east-flowing rivers.

• Deforestation, quarrying, roads and poorly planned construction can intensify runoff, soil erosion and slope instability in these high-rainfall catchments.
• Environmental impact assessment must therefore consider terrain, drainage, slope stability and cumulative impacts within river basins.