2021-01-12 21:14:50
Jakarta, the capital of Indonesia and the fourth most populous city in the world, is sinking. Some areas do so at a rate of 25 cm per year. Certain models indicate that by 2050, most of the city will be submerged. Although it is the most serious case of a phenomenon called “subsidence”, it is not an isolated event. In China, widespread subsidence affects developed cities in major sedimentary basins. In Europe, the Netherlands has 25% of its territory below sea level due to the impact of land subsidence and, in Italy, the subsidence of the Po river plain affects 30% of the Italian population and contributes to Flooding during extreme high tides in Venice. In Spain, the Murcian city of Lorca is sinking at a rate of 10 centimeters a year, the largest land subsidence due to water extraction in all of Europe. In America, in the United States, the Central Valley of California has sunk up to 9 meters during the last century and in Mexico large densely populated regions have among the highest subsidence rates in the world reaching 30 cm per year.
Subsidence can be due to several causes, some of natural origin and others caused by human activities, says gerardo herreraour guest on Talking to Scientists and lead author of a study published in Science entitled: Mapping the global threat of land subsidence. Among the causes that have a natural origin are the changes due to tectonic movements, movements in the lava pockets that exist in the magmatic chambers that feed the volcanoes, or the dissolution of certain rocks by groundwater. Regarding the causes caused by human activities, the most important is the exploitation of aquifers, although the excavations carried out in mining operations, the construction of tunnels or the excess mass accumulated by buildings also influence the subsidence of the land. in large urban areas.
The case of Jakarta is a dramatic example of what happens when groundwater is exploited without control. The aquifers, when losing water at a higher rate than what their natural food sources provide, causes a compaction of the land that translates into a subsidence of the entire area. This phenomenon is very slow, it takes place over long periods of time and, depending on the aquifers, in more or less large extensions of surface. When the place affected by subsidence is close to the coast, the lowering of the land, together with the rise in sea level due to climate change, can have catastrophic consequences for the coastal population.
Gerardo Herrera Garciaresearcher of Geological and Mining Institute of Spain, and a large number of international collaborators have carried out a large-scale literature review of subsidence sites around the world. With the data obtained, they have developed a model that makes it possible to assess how susceptible a given area is to subsidence, depending on factors such as flooding and overexploitation of groundwater. According to the data provided by the study, the areas of the world where the probability of potential collapse is high or very high affects regions currently inhabited by more than 1.2 billion people. The potential subsidence threatens 484 million people who live in flood-prone areas, 75% of whom live in river areas and 25% live near the coast.
As noted in the article, during the century XXI Large variations in climate are expected due to climate change. There will be a rise in sea level and more frequent and severe floods and droughts. Prolonged droughts will have a notable effect on the contributions of water to the aquifers and will increase the consumption of the populations that are supplied from them, intensifying the subsidence of the land. The model forecasts indicate that by 2040 the threatened population will increase to 1.6 billion, of whom 635 million will live in flood-prone areas.
I invite you to listen to Gerardo Herrera, a researcher at the Radar and geohazard modeling laboratory in it Geological and Mining Institute of Spain.
References:
Gerardo Herrera-García et al., Mapping the global threat of land subsidence Science 01 Jan 2021, Vol. 371, Issue 6524, pp. 34-36 DOI: 10.1126/science.abb8549
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