The Mexico City Metropolitan Area (MCMA) had a rapid demographic and urban growth during the second half of the twentieth century that led to development of an intense Urban Heat Island (UHI). In the urbanized zone, the mean maximum and minimum temperatures have had significant increases of the order of 3 and 4°C during the last one hundred years. Even more, the areas of larger mean annual temperature approximately match the urbanization patters, showing the MCMA UHI has expanded to the eastern – northeastern and northwestern zones, along with the urbanization. There has also been a change in the precipitation regime over most of the city, since annual mean precipitation, for instance over the western part of the MCMA, has increased in almost 40% during the last century. In summary, the natural hazards related to warm spells (maximum temperature > 30 °C) or intense storms (precipitation > 20 mm/day) have increased along with the UHI. When some factors of the MCMA vulnerability are considered (i.e., loss of natural vegetation), it is concluded that the urban growth of the region has led to higher climatic risk and to more negative impacts, such as urban floods.