Even with the tremendous effort of draining the basin, seasonal floods remain a concern. Between 1980 and 2011, rain-related flooding incidents occurred every year and caused severe traffic disruptions, damages to business, homes and residents.2 During the rainy season, the metropolitan area experiences high-intensity rainfall in a short amount of time. A single storm can produce as much as 10% of the total average annual precipitation (see ANIS, 1995). The southern parts of the metropolitan zone, along the area with the highest elevation, exhibit high risk levels. But the area at risk extends north beyond high-risk municipalities and delegaciones along the border between the Federal District and the State of Mexico. From 2010 to 2013, the delegaciones and municipalities along the northeastern border between the Federal District and the State of Mexico experienced several severe spells of rain that led to declarations of states of emergency (Figure 4.1, left panel).