Context

• Recently, thousands of trees lay dead and strewn around the western parts of the Nilgiri Plateau in southern India.

Key Details

• On August 8, 2019, the Avalanche and Emerald valley regions, which are part of the Kundha watershed, received an unprecedented 900 millimetre (mm) rainfall within 24 hours.
• It broke the record for the highest rainfall in Tamil Nadu, by nearly twice the amount.
• To put this in perspective, Coimbatore, the nearest city in the plains of Tamil Nadu, receives 600 mm of rain annually.
• The Kundha watershed bore a deluge that was four times the annual rainfall amount.

Shola-grassland mosaic in danger

• The cloud forest ecology, known as sholas, grows along the folds and valleys of these mountains.
• They are old-growth vegetation and harbour several endemic and rare species of flora and fauna.
• These naturally confined forests are already some of the most endangered forest types because of habitat loss and destruction.
• The montane grasslands occur over larger portions of the mountains here, covering all the other areas that sholas do not grow in.
• Together, the shola-grassland mosaic is most adept at absorbing high rainfall amounts and releasing it slowly throughout the year, giving rise to perennial streams.
• The native tussock grasses are highly adapted to hold the soil strongly together on steep slopes. 
• The shola-grassland mosaic ecology cannot withstand the tremendously high amounts of rainfall (over 2,400 mm) that occur in significantly short periods (over four days). 

Back to Basics

• The Kundha river, which is a primary tributary to the Bhavani that feeds into the Cauvery, is fed by numerous streams and rivulets at the headwater sections. 
• Gone are the rich black soil layers topped with spongy humus that line the streams; washed away are the dark moss and wild balsam covered rocks that shaped the flow of every stream; lost are the thousands of shola trees, dwarf bamboo and forest kurinji (shrubs of blue flowers which covered the hills) that guarded the streams, saplings, ferns and orchids of the forest floor.
• In place of these are deep cuts of gauged out Earth, revealing the underlying lateritic soil and rocks.
• The Kundha watershed region can be broadly divided into two — the higher slopes and the descending valleys.
• Shola-grassland ecology dominates the higher slopes with various types of land uses such as tea cultivation, vegetable farming, villages and non-native tree plantations dominating the descending valleys.
• The Kundha Hydro-Electric Power Scheme is one of the largest hydropower generating installations in Tamil Nadu with 10 dams.