Because cities contain many roofs, paved roads, parking lots, and other hard surfaces, they seal the ground and alter the water cycle by reducing rainwater infiltration. In Nogales, Sonora and Nogales,, Arizona, all the rainwater that is not absorbed by the soils or trees during the monsoon concentrates and runs speedily through city streets, often causing floods and contamination.
Associate professor Francisco Lara Valencia, is leading a project seeking to restore the natural water cycle in Ambos Nogales by researching and promoting the use of urban green infrastructure.