‘Coastal areas to see more dry spells next 30 years’

Interiors may see more wet seasons, says varsity study

Localities close to the coast in Chennai are expected to witness dry periods frequently over the next three decades, says a study by Anna University calling for a decision-support system for drought and management of reservoirs.

According to a study on spatio-temporal rainfall and meteorological drought by Department of Geology, Anna University, the localities near the coast such as Mylapore, Chepauk and Nungambakkam may experience dry spells more frequently in the coming decades.

(The dry period is arrived based on the assumption that rainfall is less than 5 mm for more than 60 days).

For instance, the number of times the dry conditions may occur in Nungambakkam is predicted to be in the range of 68-103 times between 2021 and 2099, said Anandharuban P., a research fellow and one of the authors of the study. It was funded by the Department of Science and Technology (Water Technology Initiative).

But interior areas like Sriperumbudur, Chembarambakkam and Kattankulathur may experience less dry period. For instance, dry conditions may recur 24 to 38 times at Chembarambakkam in the coming decades till 2099. In Kattankulathur, the number of times a dry spell can occur may vary from 22 to 35.

Similarly, wet spells, where more than 200 mm of rainfall occurs in a span of two days, may be higher in interior stations compared to those near the coast. For instance, the frequency of wet spells in Meenambakkam may repeat for 15-22 times in the next decades till 2099. In Chembarambakkam, the number of wet spells may recur for 91-144 times during the period between 2021 and 2099. While the average annual rainfall in the city may increase by 100 mm between 2021 and 2050, there may be a slight decrease in rains from 2051 to 2099.

The trends in rainfall in the coming decades were arrived using various general circulation models (GCMs) of international weather agencies. The GCM projected rainfall was scaled down by regional climate model of the Indian Institute of Tropical Meteorology, Pune, for predictions for the city and the Adyar river basin.

L. Elango, professor, Department of Geology and the study’s corresponding author, said the inflow pattern in reservoirs was dependent on the rainfall. The data of projected rainfall would help in decisions on operation of reservoirs. Various global weather parameters, including sea surface temperature and wind circulation, were analysed for the GCM.

Besides urban heat island, one of the reasons for increase in dry conditions and intense rainfall days could be the impact of green gas emission on climate change. The changes in air circulation pattern and sea surface temperature may impact rainfall pattern in coastal and interior areas in the next few decades, Prof. Elango said.