An extraordinary weather event, there was an average of 257 litres per square metre of rainfall

An extraordinary weather event, there was an average of 257 litres per square metre of rainfall.

10-02-2021R.S.

The regional environment ministry is in the process of installing 21 new gauging stations in torrents in the Balearics. When these 21 are installed, there will be 41 in all - 32 of them in Majorca. The 41 torrents in question, it is said, represent the most dangerous. The dangers are all too obvious and all too fresh in the memory - devastating and fatal floods.

The gauges are in the beds of torrents. They consist of small wells with measuring probes. The water enters these wells and solar panels generate the energy to transmit flow data in real time. Technicians can therefore have immediately available data in order to analyse torrent capacity and therefore also the potential for water to overflow.

The twenty existing gauging stations are more than twenty years old. They will all be modernised. The analog data that they capture are essentially retrospective in that the stations merely store data that have to be collected by technicians. While they supply some useful information, they aren’t of much benefit if there is a major weather event. And we sadly all know what that means.

The torrents to be monitored in real time include Ses Planes in Sant Llorenç. Two days after the tragedy in October 2018, Miquel Grimalt, professor of physical geography at the University of the Balearic Islands, described the torrent as “very dangerous” because of the sheer volume of water that flows. He explained what we came to understand and what was so transparently obvious when one stopped to think about it.

An extraordinary weather event, there was an average of 257 litres per square metre of rainfall. Researchers at the university were to later conclude that over a fifteen-minute period the torrent accumulated a flow of 442 cubic metres per second, equivalent to the River Ebro, which rises in Cantabria, flows into the Mediterranean at Tarragona, is 930 kilometres long and has a thousand times more space.

The width of the torrent, allied to the velocity of the water pouring down from the nearby mountains and the comparatively short distance the water had to travel contributed to the perfect conditions for disaster, as did the proximity of development and the low bridges which impeded the flow. What was it they reckoned? Five-metre-high walls of water that crashed out.

The new gauging stations are welcome, but even these will be of only so much use. Miquel Mir, the environment minister, says that nothing in Sant Llorenç could have predicted, could have given data to have prevented disaster. “Everything happened in the space of fifteen minutes.” It was that accumulated flow, equivalent to the Ebro.

More than two years on from the tragedy of Sant Llorenç, there are now to be 21 new gauging stations. Sant Miquel in Sa Pobla, Sa Riera in Palma, Sant Jordi in Pollensa, other torrents in the Tramuntana and elsewhere will be among the beneficiaries. Yet while they clearly do offer an important means of alert to the risk of flooding, they are only one means.

The rainfall in October 2018 was colossal but it wasn’t unique. It will happen again. The rain may be elsewhere and the geography and conditions such that torrents don’t pose as great a danger as Ses Planes. But what was exposed in Sant Llorenç were apparent failings in communication and in Aemet’s forecasting. It shouldn’t be forgotten that the red alert was issued at 9pm on that fateful evening. By then, the thirteen people who perished were already dead. Fifteen minutes; fifteen minutes at around seven in the evening.

The rainfall wasn’t unique but it was in a way a freak. This was because it was so localised. One can contrast what happened in Sant Llorenç with the previous ‘torrentada’ that claimed lives in Majorca. That was in September 1989. The three deaths were in Portocolom, and yet Portocolom wasn’t the epicentre. Manacor, S’Illot and Porto Cristo were most affected when half a year’s rainfall came down over a three-hour period. But a point about that event was that there was short-notice prediction. At half seven on the morning of September 6, police were turning cars back from Porto Cristo before the storm hit. Twenty-nine years later, and there didn’t seem to be quite the same anticipation.

The monitoring of the torrents is absolutely essential, as is their maintenance. The environment ministry has been criticised for not managing the torrents adequately, but even if there is debris or too much vegetation, this is largely irrelevant in the face of a force of nature, a force which will recur and - in all likelihood - more often. Data can offer so much, Aemet can forecast so much, but if circumstances conspire, as they did in Sant Llorenç, it only takes fifteen minutes.

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