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Climate Change and U.S.-Mexico Border Communities 365Figure 16.6 Over-drafted aquifers in Mexico. Note the concentration of these in northeast BajaCalifornia, along the coast of Sonora, and in the Rio Grande/Río Bravo watershed. Source: CONAGUA(2011, chap. 2, 34).while groundwater quality in coastal aquifers may be affected by sea-level rise that leadsto saltwater intrusion (see Chapter 9, Section 9). Chronic salt accumulation in soils associatedwith hot and arid climates can produce agricultural losses and places additionalrestrictions on regional agricultural water management. ixxx Scientific research ongroundwater is lacking in comparison to knowledge on surface water resources, and thelack is particularly pronounced on the Mexican side (Moreno 2006; Scott, Dall’erba, andDíaz-Caravantes 2010; Granados-Olivas et al. 2012). Also, the effects of climate variabilityand change on water quality are virtually unexplored territory.There are almost no natural impoundments of any substantial size in the border region.However, there are a number of man-made reservoirs, most of which are fed bythe Colorado River or Rio Grande (examples are the Imperial and Morelos Dams on theColorado River and the Leasburg and American Dams in the border region on the RioGrande), and so are replenished by water derived primarily from winter snowpack indistant mountains. Upper Rio Grande flows in particular rely primarily on snowpack(Lacewell et al. 2010). Smaller border-crossing rivers like the Santa Cruz and the SanPedro get their most substantial flows from summer precipitation, and somewhat lessfrom winter storms and local snowpack in high elevation “sky island” mountain ranges.The New River in the Mexicali-Imperial Valley region receives its flow from treatedwastewater and agricultural drains. Numerous small reservoirs in the border regioncapture rainfall and many also store imported water from the major river systems. OfSan Diego’s twenty-five reservoirs, many import water from the Colorado River andfrom the California Water Project in Northern California. Coastal Baja California has