Kerala floods explained in six visuals

Family members shift a 98-year-old woman from their flooded home in Upper Kuttanad village of Niranom | PTI  

The ongoing south-west monsoon has wreaked havoc in Kerala, with as many as 20 people killed in rain-related incidents on Thursday, taking the overall toll to 87.

Here’s a look at how relentless rains over the past two months led to a chain of events which resulted in the floods.

Hitting a high

This year, the south-west Monsoon brought three spells of rains to Kerala — first during mid-June, second during mid-July and the third in mid-August.

The below graph shows that between June 1 and August 15, the daily actual average rainfall exceeded the normal (expected) average rainfall on 40 out of a total of 76 days.

image/svg+xml80 70 60 50 40 30 20 10 0 June 1 June 6 June 11 June 16 June 21 June 26 July 1 July 6 July 11 July 16 July 21 July 26 July 31 Aug. 5 Aug. 10 Aug. 15 Rainfall (mm) daily average rainfall normal average rainfall 127.8 mm



Also, in the last eight days, between August 8-15, the actual rainfall exceeded the expected rainfall consecutively on all days. Thus, relentless rainfall in three successive spells meant that river water levels were increasing steadily.

Idukki bears the brunt

Idukki received the maximum rainfall and also experienced the maximum departure from normal among all districts. The below maps show both actual average rainfall this south-west Monsoon season and also the departure from normal as of Tuesday.




Inflows rise

As rainfall increased, the inflow of water to reservoirs also increased, swelling their storage levels. The graph below shows inflows to major reservoirs in the past month.





Filled to the brim

The steep increase in inflows has led to storage levels in reservoirs nearing the maximum. The graph below shows storage levels in major reservoirs in the past month.

image/svg+xml Jul 15 Jul 19 Jul 23 Jul 27 Jul 31 Aug. 4 Aug. 8 Aug. 12 Aug. 15 Level of major reservoirs, which were 60-70% full in mid-July, shot up to 95-100% mid-August Kundala Idukki Mattupetty Sholayar Reservoir storage (%) 100 80 60 40 20 0



Spike in spills

After storage levels peaked, the spills (excess water deliberately released from reservoirs) have increased, flooding nearby places. The chart below shows spills in major reservoirs in the past month.

image/svg+xml Jul 15 Jul 19 Jul 23 Jul 27 Jul 31 Aug. 4 Aug. 8 Aug. 12 Aug. 15 Despite heavy rains in July, the reservoir levels were only half full and there were no spills But, in August, when heavy rains persisted, water discharge and spills increased correspondingly 60 50 40 30 20 10 0 Idamalayar Idukki Sholayar Spill(mcm/day)



Red alert

According to the Central Water Commission, if a river's water level crosses the ‘Highest Flood Level’ (HFL), then it should be labelled as ‘severe’ and a special red bulletin should be issued.

Three stations — Arangali, Kalampur and Vandiperiyar — has already breached the HFL and the levels are rising still. The table below shows present water levels as of Wednesday 7 p.m. across 21 monitoring stations in Kerala and whether the trend is rising or falling.


Corrections & Clarifications: This article was edited for a typing error. The word 'brunt' was mistakenly spelt as 'burnt'.

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Printable version | Feb 21, 2021 12:48:53 AM |

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