Change in land use increases the temperature in cities

The constant change in land use in large cities is a factor that must be added to the increase in general temperature, since the loss of bodies of water, green areas and the growth of the metropolis could cause an increase of one more degree of temperature by 2060, revealed a study carried out by Erika Danaé López Espinoza, an expert from the Institute of Atmospheric Sciences and Climate Change of the UNAM (National Autonomous University of Mexico).

Before the coordinator of the Climate Change Research Program (PINCC), Francisco Estrada Porrúa, the researcher detailed that when reviewing the behavior of society regarding land use (without taking into account the effect of climate change or the heat island) it is possible to observe that the disappearance of the bodies of vital liquid generates an increase in temperature and a reduction in rainfall in Mexico City, Hidalgo and the State of Mexico.

Before the coordinator of the Climate Change Research Program (PINCC), Francisco Estrada Porrúa, the researcher detailed that when reviewing the behavior of society regarding land use (without taking into account the effect of climate change or the heat island) it is possible to observe that the disappearance of the bodies of vital liquid generates an increase in temperature and a reduction in rainfall in Mexico City, Hidalgo and the State of Mexico.

In the last session of the module "What do we know about climate change in Mexico?", organized by the PINCC, López Espinoza explained that part of his research is dedicated to reviewing what would happen if we had a different type of land use than the current one, especially in the future.

"The increase in the average temperature in this scenario of urbanization is presented, mostly, with increases in Tláhuac and Xochimilco with 0.8 and 1 degree Celsius more for Mexico City. For the State of Mexico in Zumpango, Tepotzotlán, Ecatepec and Texcoco with increases of 1 to 1.3; and in the Hidalgo basin and Llano de Tula with 1.1 degrees of temperature increase".

Globally, the rapid expansion of urban areas represents one of the most notable human transformations of our planet because it requires transportation infrastructure, housing space, food inputs (planting and raising livestock), and, consequently, the occupation and change of land cover and land use. The World Bank estimated that in 2021, 56.6 percent of the population will live in large cities.

Mexico City experienced rapid population growth during the 20th century, driving the incorporation of rural peripheral areas, which are characterized by a horizontal pattern of occupation and lack of compliance with urban regulations.

The researcher from the Ocean-Atmosphere Interaction Group recalled that around 1500, with the foundation of the Aztec kingdom in a large body of water, a drying process began, which intensified during the colonial era and the modernization of the landscape, altering meteorological and climatic patterns.

These bodies of water on land play an important role in regulating the climate of the region because of their physical properties that help reduce extreme temperatures during the day, also because they are a strategic source of moisture and a significant source of latent heat flow that emits.

Tenochtitlan was located on an islet in Lake Texcoco, Zumpango, Xaltocan, Xochimilco, and Chalco, with an area of 1,500 square kilometers (km2) that is said to have a depth of up to 11 meters at its lowest point.

With this information, Lopez Espinoza and her team set themselves the task of simulating on the computer the climatic conditions on the surface of the ground or land with this lake system, which was compared with the current conditions of the same surface; that is, the city and the aquatic remnants.

This large lake system works as a temperature regulator during the day, and we observed that the differences in the maximum and minimum temperature would be 2.5 to 2.8 degrees Celsius; that is, with urbanization we have warmer days and colder nights.

Regarding rainfall, the specialists observed an increase in precipitation when lakes are present, especially in the early hours of the day, which means that it used to rain more; while without these bodies of water in large cities, daily accumulated precipitation is reduced by an average of 500 millimeters per month.

With these results, the experts questioned what will happen in 40 years (in 2060), because according to the National Population Council, the number of inhabitants will continue to increase, especially in the metropolitan area, particularly in the State of Mexico.

If the current growth of the metropolitan zone continues, it would reach 3,622 km2, which would imply the loss of 63 percent of pastures and irrigated agriculture, and 23 percent of agricultural areas, in addition to the loss of 13 percent of scrubland, scarce vegetation, bodies of water and evergreen forests, commented López Espinoza.

According to predictions, by 2060 the change in land use occurring in this zone will reach beyond its area and the entity with the greatest impact on temperature is the State of Mexico, where the greatest modification will occur with the loss of vegetated regions to urban areas, followed by the State of Hidalgo and Mexico City.

The university professor warned that this situation causes the lack of access to public services, added to deficient housing conditions, making Iztapalapa, Tláhuac, and Xochimilco the most vulnerable municipalities in the country's capital. In the case of the state of Mexico, the most affected municipalities are Tultitlán and Ecatepec; and the Hidalgo basin, in Hidalgo.