Impacts of Climate Change and Land Use on the Southwestern United States
Land Use History of North America (LUHNA): Repeat Photography


Figure 12 & 13 - In 1910, N. H. Darton recorded the progress of arroyo-cutting on San Vicente Wash, the stream that runs through the town of Silver City, New Mexico. A few years prior, arroyo-cutting had gouged a huge gully through Main Street (Alford 1982). An arroyo has been extended upstream and maintained during the past 85 years, indicating that recovery rates from channel entrenchment may take centuries.


Figure 14 & 15 - In July and August of 1890, heavy flooding cut a deep channel in the Santa Cruz River at Tucson, starting at an intercept ditch with an unprotecting heading. Arroyo cutting destroyed the Silver Lake, which turned the waterwheels of local flour mills and provided irrigation water for agricultural lands downstream. Compare these photographs of Silver Lake in 1891 and 1982 (Betancourt and Turner 1988).


Figure 16 & 17 - Since World War II, ground-water withdrawals have reduced wetlands and riparian vegetation in southwestern valleys. Mining of ground water in the Tucson Basin, for example, destroyed mesquite forests in the bottomlands of the San Xavier Indian Reservation between 1940 and 1982. Such wholesale conversions of floodplains makes recovery from arroyo-cutting impossible on century time scales.


Figure 18 & 19 - Many southwestern floodplains, including the Rio Grande (Albuquerque, Las Cruces, El Paso), the Salt River (Phoenix), and the Santa Cruz River (Tucson) have been heavily urbanized. Compare these photographs of the Santa Cruz River floodplain in the 1890s and 1980s. Restoration of these downstream reaches are no longer possible, as is the case downstreams of dams (Collier et al. 1996).


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