Risk of urban flash floods in the Guadalajara Metropolitan Area, Mexico

The Guadalajara Metropolitan Area (GMA), in western Mexico, has experienced a rapid demographic and urban growth in recent decades. As a result of land use changes, an Urban Heat Island (UHI) has developed and intensified, which reflects not only in air surface temperature increases, but also in higher atmospheric moisture content and more intense precipitation events. Storms have become more frequent since the beginning of 1980s, which makes them one of the major meteorological hazards for the city. Such an increase in strong storms appears to be related to the urbanization process which in turn, has increased the vulnerability of the GMA to intense rains. The urban expansion towards the higher parts of the region has led to more water runoff and flash flood events in the low-level parts of the metropolitan area. An analysis by means of observed meteorological data and a rainfall – runoff methodology shows that the combined effect of increased precipitation and vulnerability results in a higher risk of urban flash floods. The loss of natural vegetation, the main roads that act as water channels that converge into the central part of the city, an insufficient drainage system and the lack of prevention actions have resulted in more frequent urban flash floods. All of these vulnerability factors are associated with an inadequate urban expansion process. The model of flood risk may be used to define adaptation measures to face a changing climate.