Scientists claim that the region has been undergoing recurrent changes from a dry zone to a wet zone and vice-versa. Since the process is repetitive, they say that there is a high probability of desertification of the 500 sq. km area and possibly more.

Researchers from the city-based National Geo-physical Research Institute, Geographical Survey of India and the Physical Research Laboratory in Ahmedabad studied sand dunes around Kanigiri in Prakasam district.

They noted that the occurrence of sand dunes about 75-80 km from the present coastline was peculiar. Their findings were published in the journal Quaternary Research recently.

The researchers studied the age of the grains of sand from the dunes using optical dating techniques. “The oldest deposition was found to be about 90,000 years ago when it could have been a desert. There was probably a long wet phase 50,000 to 85,000 years ago,” said Dr Devender Kumar, senior scientist, NGRI.

Scientists also said that the periods of transition from arid to less arid phases occurred between 45,000 to 48,000 years ago, 30,000 to 33,000 years ago, 21,000 years ago, 11,000 years ago, 46,000 years ago, 17,000 years ago and as recently as a few hundred years ago.

It is noteworthy that the time gap between successive phases, when the region turned into a desert, has been shortening over the millennia.

“This process will repeat in future and it is quite common in other parts of the world. The process is hastening due to anthropogenic factors,” Dr Venkat Reddy, senior principal scientist, NGRI and lead author of the study, said.

While these are spurts of desert phases in a semi-humid phase, wet phases amid largely dry ones and vice-versa have also been reported in other parts of the world. A paper in the Proceedings of the National Academy of Sciences spoke of the wet phases in the Sahara desert. Even the Thar desert may be experiencing similar climate change patterns.