KOCHI: Keralam was experiencing hot weather conditions for the past three weeks. The development of a low pressure area in the Bay of Bengal changed wind pattern and there was havoc. Three hours of intense rainfall reversed the weather, triggering landslides and flash flood in the high ranges and leaving nine persons dead. Meteorologists opine that climate change and El Nino have made weather forecasting difficult as a depression or a change in wind pattern can trigger intense rainfall.
The state had witnessed a prolonged dry spell during the past three weeks and the mercury had breached 35 degrees Celsius in many districts. The Southwest monsoon had started withdrawing and conditions similar to Northeast monsoon were prevailing. The formation of a low pressure area in the Bay of Bengal changed the weather pattern and as the moisture content in the atmosphere was high it triggered intense rainfall, explain meteorologists.
“High day time temperature provides conducive atmosphere for development of thunderstorms. The wind was blowing in the north westerly direction till Friday. The westerly wind gathered momentum under the impact of the depression and there was a vertical extension of cloud that triggered intense rainfall along the high ranges. There will be moderate rainfall on Tuesday but we can expect an intense spell on Wednesday as the system in Bay of Bengal makes landfall in Andhra Pradesh. We can expect heavy rain from Wednesday to Friday,” said IMD Keralam director Neetha K Gopal.
The immediate trigger for the flash flood appears to be highly localised, intense rainfall over the upper catchments, says Roxy Mathew Koll, climate expert and scientist at the Indian Institute of Tropical Meteorology, Pune.
“In Keralam’s hilly terrain, water is rapidly funnelled into streams, producing sudden surges downstream.
Where slopes have already been weakened by continuing rain, slope modification or land-use changes, the same downpour can also trigger landslides,” he said.
“A warm climate along with a warmer Arabian Sea now supplies more heat and moisture, increasing the potential for short, concentrated downpours. For Keralam, we see a clear shift in the monsoon pattern. The total amount of rainfall is declining, while extreme rains in short spells are increasing. As a result, Keralam may have a deficient monsoon season like this year where it is 28% deficit, and still suffer a deadly flash flood,” said Roxy.
To reduce the impact of climate disasters, Keralam needs denser rainfall and river monitoring, catchment-level impact forecasts, rapid downstream alerts, and immediate restrictions at vulnerable slopes, riverbanks and tourism sites when heavy rain occurs upstream. Our warning systems must move beyond telling people how much rain may fall to what that rain could do, and where people should not be, he explained.
The rainfall during the past couple of days may reduce the monsoon deficit and improve the storage in reservoirs, but it will not help recharge the ground water resources, said C P Priju, principal scientist at the Hydrology and Climatology division of the Centre for Water Resources Development and Management (CWRDM).
“Most of the rainfall happened in the eastern side of the state which are the high ranges. As it was an intense rainfall, the water flowed down rapidly as surface run off and entered the sea. So it may not help replenish the ground water resources. If the Northeast monsoon fails, Keralam may face drought conditions by March. The underground resources in certain areas have hit critical levels due to over exploitation by borewells,” he said.
Forecast
Moderate rainfall on Tuesday
Rain may intensify on Wednesday
Heavy rain expected from Sept 23 to 25
Southwest monsoon starts withdrawing
Dry spell, hot and humid conditions to prevail next week
Expect thunderstorms any time as high day time temperature, moisture content in atmosphere provide conducive atmosphere.
Rainfall in Vagamon
19/9: 27.2 cm | 20/9: 25.2 cm