The Central Water Commission, a technical organisation under the Ministry of Jal Shakti, releases a bulletin on reservoir levels every week. The bulletin issued on August 1 said the water level in reservoirs across the country was 80% of normal storage – or 20% less than usual. Two weeks later, as per the bulletin released on August 14, this had jumped to 125% of normal storage.

The jump in water levels is because of heavy rainfall, which in turn can be traced back to an atmospheric depression, or an area of low pressure in the air.

A depression is created when the air in an area warms up. Warm air is lighter than cool air, and so it rises, leaving a vacuum in its wake. This vacuum sucks in air from the surroundings in order to fill itself. The warm air cools as it rises, until the water vapour in it condenses and comes down as rain.

The monsoon rains themselves happen because of such a seasonal depression, called the monsoon trough. Last week though, the depression caused a cyclonic circulation: a swirling vortex that drew more and more moisture-laden air into itself until it all came down in a deluge.

Full reservoirs

On the ground, the deluge has caused severe floods in parts of the Indian peninsula – in states like Kerala, Karnataka, Maharashtra and Gujarat. It has also filled up water reservoirs.

South India still remains covered by clouds, which makes it hard to view the state of its water reservoirs through satellite images. However, the clouds over Gujarat and Maharashtra have cleared enough for the Jayakwadi and Ukai reservoirs to be visible.

The reservoirs appear markedly fuller than they were in late July. They also appear much fuller than they did in September of last year. September is when the monsoon season ends, so it is the month when the reservoirs are usually at their fullest. An August 2018 comparison proved impossible because of the thick cloud cover in satellite images through that month.

The Jayakwadi reservoir on the Godavari river is at 92% of its full capacity, as against a 10-year average of 24%.

Source: Sentinel Hub

The Ukai reservoir on the Tapi river is at 78% of its capacity, as opposed to its 10-year average of 56%.

Source: Sentinel Hub

Changing rainfall patterns

The average temperature between 2011-’18 was 0.65 degrees higher than the average temperature in the decade of 1901-’10, according to environmental statistics released by the Ministry of Statistics and Programme Implementation. This is part of a trend showing a steady rise in the average temperature, as a result of global warming caused by human activity.

Warmer air can hold more water vapour than cooler air. This means that when average temperatures are higher, there is more water vapour in the air. This extra moisture enters the cyclonic circulations, which results in heavier rainfall.

The cost of extreme precipitation

The reservoirs are now full, which means that with proper management, most cities won’t run out of water for another year. But the deluge has come at a heavy cost.

At least 496 people have died due to extreme rainfall-related causes so far in 2019. Last year, 2,045 people died for the same reason.

In 2018, the floods in Kerala alone damaged over 6.5 lakh houses, and affected 1 lakh hectares of crops. The cost of the floods was estimated by the state government as Rs 5,597 crores.

Not only are extreme precipitation events occurring more frequently, they are causing greater destruction – as Kerala showed, largely because of an increase in construction and quarrying in ecologically sensitive regions.