The sinking of Mexico City has come to a point where the Zócalo, the main square in the historic city centre, is at a lower elevation than lake Texcoco, reports Mexico News Daily.
Groundwater overdraft is depleting the aquifers beneath the city, causing it to sink. This has been ongoing since the mid-19th century, according to Fernando González Villarreal, a researcher at Mexico’s National Autonomous University, UNAM. Although the aquifers are replenished, the rate of recharge is only about 50% the rate of groundwater extraction.
Mexico City is built on the basin of ancient Lake Texcoco, the largest of several lakes of which only remnants remain, most of them drained to control flooding. Much of the ancient endorheic lake basin was fed from groundwater aquifers. The consequences of the draining, completed in the 20th century, were enormous: the area turned semi-arid and currently the city experiences water scarcity. In addition, soft lake sediment underneath the city has made it vulnerable to soil liquefaction during earthquakes.
Because the sinking is not even across the city, buildings tilt to the side, and pipes break: as a result, repairs and maintenance are expensive. Some areas of the city sink as fast as 40 centimetres per year, and it is estimated that overall the city has dropped 10 metres in a century.
González urges action to address the issues, such as finding alternative sources of drinking water, artificial aquifer recharge and renovating the water infrastructure, some of which are more than 100 years old. The measures may cost up to US $1 billion per year, for the coming 15 years.
Mayor Claudia Sheinbaum Pardo is committed to solving the water problems the city is experiencing, and has called for collaboration on the issue in order to move forward.