The Regional Impacts of Climate Change

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Climate change impacts on hydrological cycles are expected to be greatest in semi-arid and arid areas; on lakes and streams in high evaporative drainages; in basins with small catchments and relatively short retention times; in shallow lakes, streams, and rivers in which appropriate thermal refugia are not available; and on irrigation systems that rely on isolated reservoirs or snowmelt from seasonal snowfall (IPCC 1996, WG II, Chapters 7 and 10). The implications of climate warming on the hydrological cycle and its consequences for precipitation distribution, intensity, and timing; surface runoff; and underground water resources will be aggravated in certain areas by population growth and unsustainable development of water-consuming activities. Country studies undertaken to satisfy commitments under the UNFCCC indicate the vulnerability of Latin American communities that are dependent on water resource availability. In this respect, reduced precipitation has had serious consequences for hydropower production in Central American countries; for example, ENSO events during the past decades in Costa Rica led to significant reductions in runoff and consequently to a higher demand for thermal energy production (Campos et al., 1996) (see Figure 6-5). On the other hand, increased precipitation (up to 35% in the province of La Pampa) has been observed in the Pampas-the most important area for grain and livestock production in Argentina (Canziani et al., 1987; Forte-Lay, 1987; Vargas, 1987). The benefits from such an increase in precipitation have been offset by more frequent extreme precipitation events and higher risks of flooding.

Figure 6-5: Precipitation and maximum temperature anomalies for the Pacific coast of Costa Rica resulting from ENSO phenomena and changes in electricity generation types.

Extreme precipitation events could increase the number of reservoirs in the humid tropics that silt up well before their design lives have been reached. Poor management of a basin (e.g., severe deforestation in drainage areas, especially in the case of rivers flowing along deep valleys) would increase erosion and interact with hydrological changes, causing siltation and decreasing the potential for hydroelectricity generation (Bruijnzeel and Critchley, 1994; Campos et al., 1996).

Lakes have individualistic and often rapid responses to climate changes. Lake Titicaca, for example, experienced a 6.3-m rise in water level from 1943 to 1986 (IPCC 1996, WG II, Section 10.5.2). This increase exceeds by a factor of 40 the change in mean sea level estimated from global warming. Fluctuations in lakes with large temporal changes in water level are expected to be aggravated by climate change. Changes in mixing regimes also are projected as a result of climate change in temperate zones because of increases in winter air temperatures-with potentially large effects on biota.

Wetlands are distributed throughout the region but are more extensive in the tropics and subtropics. The effects of climate change on wetlands remain very uncertain (Gorham, 1991; IPCC 1996, WG II, Figure 6-1). Human intervention may be more critical than climate change in affecting these ecosystems.

Freshwater fisheries and aquaculture generally could benefit from climate change, though there could be some significant negative effects, depending on the species and on climate changes at the local level. Positive factors associated with warming and increased precipitation at higher latitudes include faster growth and maturation rates, lower winter mortality rates from cold or anoxia, and expanded habitats as a result of ice retreat. Offsetting negative factors include increased summer anoxia, increased demand for food to support higher metabolisms, possible negative changes in lake thermal structures, and reduced thermal habitat for cold-water species. Individual effects are difficult to integrate. However, warm-water lakes generally have higher productivity levels than cold-water lakes; because of the latitudinal distribution of projected warming, warm-water lakes will be in areas with the least change in temperature. It is reasonable to expect higher overall productivity from freshwater systems. Finally, fishery managers heavily manipulate freshwater fisheries, and aquaculture is expanding in many Latin American countries. If species mixes continue to be changed to support angler and market preferences and changing habitats, climate-change damages may diminish while benefits increase.

Impacts on biota-including commercial and subsistence fisheries-are expected to be most pronounced in isolated systems, such as high-elevation Andean lakes or lakes in the far south of Argentina and Chile, as well as in areas in which species are close to their geographical distribution limits. Within large drainage systems, flexibility for migratory shifts to compatible temperatures will be greater in north-south flowing systems (Meisner, 1990; IPCC 1996, WG II, Sections 10.6.1.2, 16.2.1).

The effects of climate change on freshwater ecology will interact strongly with anthropogenic changes in land use, waste disposal, and water extraction. Regional water resources will become increasingly stressed because of higher demands to meet the needs of growing populations and economies, as well as temperature increases. These anthropogenic effects are expected to increase in Latin America, and there is a risk that these impacts will extend to tropical streams and wetlands that, owing to their remoteness, have so far escaped the impacts of human activities (Armentano, 1990; IPCC 1996, WG II, Sections 6.3 and 10.2.2).

Conflicts may arise among users and regions and among Latin American countries that share common river basins. The effects of climate change on agricultural demands for water, particularly for irrigation, will depend significantly on changes in agricultural potential, prices of agricultural produce, and water costs (IPCC 1996, WG II, Chapter 14), as well as on other consumptive uses. Water availability in two countries of the region (Mexico and Peru; see Box 6-3) is expected to decline significantly with respect to the present climate. Furthermore, as has happened in the past, reductions in or a lack of freshwater availability, or cases of excess leading to flood conditions, may lead to interstate or international conflicts or invasion of neighboring territories by "campesinos" in distress.