A villager wades through the flooded Kawas village near Barmer on Monday. (PTI)

New Delhi, Aug. 28: A rare combination of weather events, local terrain and geology colluded last week to turn a sand dune-dotted desert land around Barmer district in western Rajasthan into India’s latest flood zone.

While Barmer recorded about 58 cm rain over three days — twice the rainfall that India’s desert region receives in an entire monsoon season — the sand and a layer of gypsum beneath the sand were other reasons for the flood, weather scientists said.

“The water-holding capacity of sandy soil is lower than that of clay-based soils,” said Laxman Singh Rathore, a senior scientist at the National Centre for Medium Range Weather Forecasting near New Delhi.

“And about 10 feet beneath the sand, there is a layer of gypsum which is nearly impermeable and the water has accumulated in low-lying areas wherever there is no natural drainage.”

But it was a low-pressure zone that had moved westward from the Bay of Bengal across central India and then — defying the conventional behaviour of such low-pressure zones — persisted over Rajasthan for a full three days that contributed to the heavy rains.

Such low-pressure zones that form over and pick up moisture from the Bay of Bengal during the monsoon months typically weaken as they move over the land and vanish over the hot desert.

However, for the past 45 days, each of the low-pressure zones that formed over the Bay of Bengal has moved along a path south of their normal track during the monsoon season, Rathore said.

The low-pressure zone that arrived over Rajasthan last week could have drawn fresh moisture from the Arabian Sea, said Basak Bandopadhyay, a scientist with the Indian Meteorological Department.

The low-pressure zone persisted from August 21 through August 23, and rain gauges in the state recorded about 58 cm rainfall, nearly twice the 25 cm to 30 cm rain that the desert region receives each year.

The Rajasthan desert has always had deficient rainfall because of an anticyclone — a weather phenomenon in which air descends from top to bottom, warming up, reducing humidity and producing clear and dry weather.

But this year the anticyclone has shifted a bit west of its normal position, Rathore said. This is another factor that scientists believe has contributed to the transformation of a small section of the desert into a flood zone.

However, parts of the great Thar have remained as dry as always. Bikaner, for instance, about 500 km from Barmer, hasn’t experienced significant rain either in July or August, said M.S. Sahani, director of the National Research Centre on Camels.