Despite the decrease in rains, the torrentiality of Mediterranean rivers has increased – Eurasia Review
Ana Camarasa, professor of physical geography at the University of Valencia, compared the precipitation recorded in the Júcar Hydrographic Confederation between 1989 and 2018. By analyzing more than 800 precipitations and more than 140 floods on four Valencian boulevards (including the ravines de Poyo and Carraixet, south and north of Valence), the expert concludes that in the latter part of the period studied there were more risky situations, and also the avenues have intensified due to the human action by reducing infiltration and increasing overflow and surface erosion.
The analysis of data from the Hydrographic Confederation of Júcar (which manages all the Valencian rivers with the exception of the Segura basin, to the south, and the Bergantes basin, to the north), prepared by Ana Camarasa, confirms that the appearance flooding is more and more frequent. derived from periods of intense rain over shorter periods. The rains show more peaks in intensity at the onset of storms, which increases the risk of flooding and decreases the absorptive capacity of basins, as they occur in shorter periods of time. All of this is linked to the context of climate change in which we find ourselves now.
In addition, in this meteorological context, the amount of rainwater that aquifers can absorb decreases (more intensity in less time), which causes this water to add to the flow of the flood. Besides the Poyo and the Carraixet, which historically caused large-scale flooding, the rivers of the Vernissa and the stream of the Gallinera (respectively south of the province of Valencia and north of Alicante) have also been analyzed.
In addition to more precipitation in less time, additional anthropogenic factors have increased the risk of flooding in recent years. Concretely, the urbanization of ravine beds or flow absorption zones (causing less infiltration into the subsoil and the expulsion of water in greater volumes and less time) which causes an increase in flow of surface. This factor, according to Ana Camarasa in the article published in the journal Cuadernos de Investigación Geográfica, “produces an increase in these ephemeral rivers and an increase in the aridification of river systems”. Aridification (the entrainment of fertile land and the disappearance of these and vegetation) leads to less retention of flows during subsequent floods.
The objective of this research is the exhaustive study of the key aspects of Mediterranean hydrogeomorphology in general and of Valencian hydrogeomorphology in particular, of the key questions of rain-flow conversion and the generation of floods in river courses. water, as well as their evolution in the current context. environmental change. This is done with the intention of anticipating the onset of those sporadic floods that occur in boulevards, systems in most cases without retention systems such as dams and reservoirs. European Union legislation currently recognizes the specificity of these systems, as well as the risk they entail.
The work used previous research, as well as data from the Automatic Hydrological Information System (SAIH), a set of stations distributed throughout the river basins of the Júcar Hydrographic Confederation, which measure flow and rainfall at varying intervals ( every five minutes, per hourly period, per day or per month). Some of the rainy events analyzed are in October 2000 (with more than 500 liters per square meter in the provinces of Valencia or Castellón), December 2004 or October 2018, among others.
In her study, Ana Camarasa used and compared elements such as precipitation (millimeters of rain per hour); the volume of water accumulated in the basin (in cubic hectometers, one hectometer is equivalent to one billion liters of water); or flow rates, measured in cubic meters per second (one cubic meter is equivalent to one thousand liters per second passing through a point) or in liters per second and per square kilometer. With regard to precipitation, he focused during the 30 or so years of events, on the cumulative, maximum intensity, average intensity, as well as the persistence of rain in each thunderstorm.