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.
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.
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.
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.
