New Delhi, July 20: A torrential downpour that washed Delhi today and the rainfall that devastated Uttarakhand last month could be portents of shifts in the monsoon’s behaviour that have also shown up as rainfall deficits in eastern India, scientists say.
Eastern India is the only zone among the country’s four meteorological regions that has as a whole experienced deficit rainfall since the monsoon season started this year, while the traditionally arid northwest is unusually wet.
Bengal’s Gangetic plains have had rainfall 30 per cent below the expected average so far, delaying preparation of paddy seedbeds.
While Uttarakhand’s extreme event on June 16-17 may explain its 74 per cent excess rainfall, Uttar Pradesh, Punjab and even eastern Rajasthan have recorded high above-average figures.
“India’s north appears to be stealing rain from the east,” said Madhavan Rajeevan, a senior atmospheric scientist and programme director at the National Monsoon Mission, a research initiative launched last year by the Union earth sciences ministry.
While the movements of moisture-bearing winds and low-pressure systems may explain the heavy rain in the north, scientists say they are intrigued by recent trends pointing to persistent rainfall deficits in the east.
“We’ve seen rain deficits in parts of the east and Northeast over the past five years but we don’t fully understand the underlying mechanisms or even whether this is a long-term trend,” Rajeevan said. “We’ll need more observations, more research.”
The India Meteorological Department’s (IMD) annual reports show that Bihar, Gangetic Bengal, Jharkhand and Odisha have all experienced some level of monsoon rainfall deficit in three of the five years from 2008 to 2012. Studies have revealed a see-saw effect linking the east and the rest of India.
“This is the most significant pattern that explains the variability of rainfall within a monsoon season. A relatively dry east is associated with a relatively wetter rest of India,” said Devraj Sikka, a senior meteorologist and climate-change specialist.
|A waterlogged street in New Delhi, which received
“very heavy rainfall” on Saturday. Picture by Yasir Iqbal
“But even a relatively dry east will still receive quite a bit of rainfall because the east is a wet zone.”
Senior IMD scientists, however, said the cumulative deficits observed this year in parts of the east and Northeast could change in the remaining two months of the monsoon season, particularly during August, which often brings heavy rainfall.
“I think five years is not long enough to establish a trend linked to the monsoon,” said Sulochana Gadgil, an atmospheric scientist. “We need to wait and watch.”
Researchers also say that it is still too early to predict how — if at all — the observed rainfall deficits in the east and Northeast might impact farming activities there.
“The quantum of average rainfall in the east and the Northeast is high — so even a 10 per cent deficit becomes significant,” a senior government scientist said, requesting anonymity.
A Bengal agriculture department official said the deficient rainfall had prevented farmers from preparing seedbeds in major rice-producing districts like Burdwan, Hooghly, Birbhum, Murshidabad, Nadia and the two 24-Parganas.
“It takes three weeks to prepare the seedbed, and August 15 is the cut-off date for kharif cultivation. So, if these districts don’t get enough rain within a week, cultivation would be hit badly,” he said.
Scientists say the extreme rainfall in Uttarakhand —300mm in a single day — last month and Delhi’s 105mm downpour within three hours today may represent an increasing frequency of extreme weather events that climate scientists have predicted.
“This season, 80 per cent of the rainfall over the capital has come from heavy downpours,” said Rajendra Jenamani, an IMD meteorologist.