Brazil’s rains of January 12, followed by flooding and mudslides that killed over 900 people in Rio de Janeiro’s Serrana region, a mountainous area in the state of Rio, was so rare that something similar should occur only once every 500 years.
That is the conclusion of a study by the Postgraduate Engineering Program at the Federal University of Rio de Janeiro (Coppe/UFRJ).
Copies of the document have been sent to Brasilia (the presidency) and the governor of the state of Rio de Janeiro.
According to professor Paulo Canedo, a Coppe specialist in hydrology, the damage was due to a combination of factors. Initially, rainfall was not that heavy; it was, however, of long duration and left the ground saturated and unstable.
Then there was heavy rainfall when a cold front moved into the area. At the same time, there was localized intense rainfall:
“This is the famous tropical summertime rainstorm that lasts ten or fifteen minutes. On January 12 the very heavy rainfall lasted four and a half hours. Cumulonimbus clouds, as high as 14 kilometers, dumped rain relentlessly. It was like 18 consecutive summer rainstorms. The power of destruction was overwhelming.”
Canedo says there was another aggravating factor: rivers quickly clogged up with mud, boulders and trees. Those natural dams eventually burst under pressure from more water, mud, boulders and trees. The result was that powerful flashfloods roared down river valleys with devastating consequences.
“In light of the unfortunate sequence of events not much could have been done to prevent this tragedy,” declared Canedo.
“You can mitigate the effects of rainstorms, have an adequate policy for land use, for example. But you cannot avoid the catastrophe. Instead of a thousand dead, you might have 500 deaths,” he declared.