IPCC Fourth Assessment Report: Climate Change 2007
Climate Change 2007: Working Group II: Impacts, Adaptation and Vulnerability

13.4.3 Water resources

Almost 13.9% of the Latin American population (71.5 million people) have no access to a safe water supply; 63% of these (45 million people) live in rural areas (IDB, 2004). Many rural communities rely on limited freshwater resources (surface or underground) and many others on rainwater, using water-cropping methods which are very vulnerable to drought (IDB, 2004). People living in water-stressed watersheds (less than 1,000 m3/capita per year) in the absence of climate change were estimated to number 22.2 million in 1995 (Arnell, 2004). The number of people experiencing increased water stress under the SRES scenarios is estimated to range from 12 to 81 million in the 2020s, and from 79 to 178 million in the 2050s (Arnell, 2004). These estimates do not take into account the number of people moving out of water-stressed areas (unlike Table 13.6). The current vulnerabilities observed in many regions of Latin American countries will be increased by the joint negative effects of growing demands for water supplies for domestic use and irrigation due to an increasing population, and the expected drier conditions in many basins. Therefore, taking into account the number of people experiencing decreased water stress, there will still be a net increase in the number of people becoming water-stressed (see Table 13.6).

Table 13.6. Net increases in the number of people living in water-stressed watersheds in Latin America (millions) by 2025 and 2055 (Arnell, 2004).

 1995 2025 2055 
Scenario/ GCM   Without climate change (1) With climate change (2) Without climate change (1) With climate change (2) 
A1 HadCM3 22.2 35.7 21.0 54.0 60.0 
A2 HadCM3 22.2 55.9 37.0-66.0 149.3 60.0-150.0 
B1 HadCM3 22.2 35.7 22.0 54.0 74.0 
B2 HadCM3 22.2 47.3 7.0-77.0 59.4 62.0 

(1) according to Arnell (2004, Table 7); (2) according to Arnell (2004, Tables 11 and 12).

In some zones of Latin America where severe water stresses could be expected (eastern Central America, in the plains, Motagua valley and Pacific slopes of Guatemala, eastern and western regions of El Salvador, the central valley and Pacific region of Costa Rica, in the northern, central and western inter-montane regions of Honduras and in the peninsula of Azuero in Panama), water supply and hydroelectric generation would be seriously affected (Ramírez and Brenes, 2001; ECLAC, 2002a).

Vulnerability studies foresee the ongoing reductions in glaciers. A highly stressed condition is projected between 2015 and 2025 in the water availability in Colombia, affecting water supply and ecosytem functioning in the páramos (IDEAM, 2004), and very probably impacting on the availability of water supply for 60% of the population of Peru (Vásquez, 2004). The projected glacier retreat would also affect hydroelectricity generation in some countries, such as Colombia (IDEAM, 2004) and Peru; one of the more affected rivers would be the Mantaro, where an hydroelectric plant generates 40% of Peru’s electricity and provides the energy supply for 70% of the country’s industries, concentrated in Lima (UNMSM, 2004) .

In Ecuador, recent studies indicate that seven of the eleven principal basins would be affected by a a decrease in their annual runoff, with monthly decreases varying up to 421% of unsatisfied demand (related to mean monthly runoff) in year 2010 with the scenario of +2°C and -15% precipitation (Cáceres, 2004). In Chile, recent studies confirm the potential damage to water supply and sanitation services in coastal cities, as well as groundwater contamination by saline intrusion. In the Central region river basins, changes in streamflows would require many water regulation works to be redesigned (NC-Chile, 1999).

Under severe dry conditions, inappropriate agricultural practices (deforestation, soil erosion and the excessive use of agrochemicals) will deteriorate surface and groundwater quantity and quality. That would be the case in areas that are currently degraded, such as Leon, Sebaco Valley, Matagalpa and Jinoteca in Nicaragua, metropolitan and rural areas of Costa Rica, Central Valley rivers in Central America, the Magdalena river in Colombia, the Rapel river basin in Chile, and the Uruguay river in Brazil, Uruguay and Argentina (UNEP, 2003b).

Landslides are generated by intense/persistent precipitation events and rainstorms. Furthermore, in Latin America they are associated with deforestation and a lack of land planning and disaster-warning systems. Many cities of Latin America, which are already vulnerable to landslides and mudflows, are very likely to suffer the exacerbation of extreme events, with increasing risks/hazards for local populations (Fay et al., 2003). Accelerated urban growth, increasing poverty and low investment in water supply will contribute to: water shortages in many cities, high percentages of the urban population without access to sanitation services, an absence of treatment plants, high groundwater pollution, lack of urban drainage systems, storm sewers used for domestic waste disposal, the occupation of flood valleys during drought seasons, and high impacts during flood seasons (Tucci, 2001).