Soil erosion from urbanization processes in the Sonoran Desert, Arizona, USA

Cattle stock ponds on the fringe of metropolitan Phoenix, USA, experienced a wide range of land-use changes over the period from 1989 to 2009. This research measures soil erosion from watersheds of different rock types, variable relief, and land uses. Monitoring sediment accumulation behind 18 earthen berms at each major land-use transition enabled calculations of soil erosion rates. Compared with the first decade of study with more precipitation and cattle grazing, accelerated urbanization in the drier second decade increased soil erosion from wildfires by up to 4.2×, from exposure of bare ground due to building construction by up to 3.4×, and from bare ground exposure due to road and pipeline construction by up to 3.1× overgrazing alone. Stock pond watersheds underlain by granite experienced statistically significant higher erosion rates compared with watersheds underlain by metamorphic, basalt, and other rock types. Global sediment yield data for warm desert (BWh Köppen-Geiger) sites reveal that our data plot consistently with other grazed study areas with a tendency for higher area-specific sediment yields in smaller drainage areas. These sediment yield data, however, do not support previously published generalizations of anomalously high or low sediment yields from warm desert settings. Desert urbanization processes accelerate soil erosion, resulting in the need for regulatory agencies to impose new erosion mitigation strategies.