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The ecology and morphology of river deltas reflect a balance between coastal and upstream processes. Changes in freshwater flow regimes will impact deltas, although the effects probably will be smaller than those of sea-level rise. Estuary characteristics also are affected by inflows from upstream, and the relative effects of sea-level rise and changes in river flows may be similar. Saline intrusion along estuaries, associated with higher sea levels and perhaps exacerbated by lower river flows, could threaten low-lying freshwater intakes, although adaptive options (relocation) are easy to implement. Saline intrusion into coastal aquifers also is a possibility, creating severe adaptation challenges in some settings—particularly low-lying islands such as atolls. Finally, rivers bring large quantities of nutrients and other materials to the coastal zone, and these fluxes are likely to be affected by changes in streamflow volumes in particular.
Provision of water to cities—especially the mega-cities emerging in some parts of the developing world—may become increasingly problematic, with consequent effects on city growth and access to safe water. Altered river flows also may affect the ability of settlements to dispose of waste safely. Urban storm drainage is potentially very sensitive to changes in short-duration rainfall and is both expensive to install and difficult to upgrade. Finally, changes in flood flows imply changes in urban flood risk; indications are that the risk generally will increase.
The most vulnerable parts of the mega-cities are the informal settlements that do not have planned water distribution and sanitation systems. Rural populations also are exposed to climate change, and it is possible that their sensitivity to change may be greater: The urban population enjoys planned water supply systems that can adapt to changes of climate change better than unplanned systems in rural areas.
The main linkage with the finance sector is through insurance and public disaster relief. Insurance against flood losses is available in some countries, and major flood events in these countries could challenge—at least temporarily—local and perhaps international insurers.
Changes in hydrological regimes have the potential to alter health risks. Most important are potential changes in access to safe drinking water, but that is likely to be more affected by factors other than climate change (such as provision of water distribution systems and improved sanitation). Water-borne diseases and water-related insect vector diseases are more sensitive to changes in hydrological patterns (e.g., Patz et al., 1998; Checkley et al., 2000). Floods have associated health problems, and climate change also has the potential to alter contamination of water supplies (through changes in flow pathways that lead to increased leaching of pollutants and through reduced flows that lead to increased concentrations) and contamination of shellfish and fish.
A change in water availability has the potential to induce conflict between different users (Biswas, 1994; Dellapena, 1999). These users may be in the same area—cities versus farmers, for example—or they may be in different parts of the river basin. Much has been written about the potential for international conflict (hot or cold) over water resources (e.g., Gleick, 1998); where there are disputes, the threat of climate change is likely to exacerbate, rather than ameliorate, matters because of uncertainty about the amount of future resources that it engenders. One major implication of climate change for agreements between competing users (within a region or upstream versus downstream) is that allocating rights in absolute terms may lead to further disputes in years to come when the total absolute amount of water available may be different.
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