They carry out storage functions: principally, when it starts to rain heavily, they hold the initial volume rush of rainfall, preventing the sudden arrival of a large amount of water at the treatment plant.
The problem is that, in order to have them work efficiently, it is necessary to know beforehand that, effectively, it is about to rain intensely; it is estimated that a margin of six hours notice is needed in order for everything to be prepared. This is why the physicist Alejandro Fernández has undertaken trials with an innovative model for statistical prediction, applying it to the public water supply network run by the Aguas Bilbao Bizkaia Water Consortium.
The PhD thesis presented at the University of the Basque Country (UPV/EHU) is entitled, Predictive precipitation model applied to the management of the public water supply network in the metropolitan area of Bilbao. Mr Fernández studied the behaviour of the variants corresponding to precipitations within a small perimeter (10 x 15 km, approximately) and with an interval of time of between 3 and 24 hours, and investigated up to what point rainfall can be predicted under these conditions.
Mr Fernández undertook trials in order to validate the model and, to this end, he calculated the number of correct hits and the number of false alarms. He compared these with prediction methods for non-local rainfall and, as he concluded, the results proved to be superior to methods such as pure climatology or certain dynamic methods. The results, likewise, are on a par with more complex models which use Earth and satellite radar; for example, Nimrod. The thesis concluded that the proposed model could improve the management of the public water supply network in Greater Bilbao. However, he also made it clear that greater development of this model is required for the management to be totally automatic, and that for the moment human supervision is essential. Mr Fernández proposed providing more data for the model for its enhancement; such as, for example, that from local pluviometry or that gathered in real time from the radar at Punta Galea, a cape located in the Basque Country.Extreme episodes every 250 years
The researcher contrasted Gumbel and Pareto statistical methods to calculate this frequency. His aim was to find out the maximum possible thresholds, with a degree of certainty of at least 95 % regarding the intensity of possible precipitation in the region of Bilbao every certain number of years. In fact, in order to verify that the mentioned calculation complied with a minimum level of reliability, he used a computer simulation technique called Bootstrap Resampling.
According to the conclusions of the PhD, rainfalls such as that which devastated Bilbao in 1983 can happen with greater frequency than has been thought. To date it has been believed that these phenomena could only occur every 500 years at the most but, in fact, they can happen, on average, once every 250 years.About the author
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