Adaptations to climate change may be categorized as either "autonomous" adaptations-where biota and ecosystems respond and change of their own accord-or "planned" or "conscious" adaptations, undertaken by humans. The primary option for conscious adaptation measures in respect to near-natural ecosystems is land-use management. This includes modification of land clearing, forestry practices, fire management, rangeland animal stocking rates, pest animal management, control of herbaceous and woody weeds, development of corridors for species migration, resting and rehabilitating degraded areas, and the consideration of climate change in management plans for urban, coastal, catchment, and other zones. Implementation of riparian (riverside) management practices and selective planting of upslope source areas would mitigate many of the adverse impacts of land development and hydrological changes on water quality and habitat values of streams, rivers, and ultimately lake and estuarine habitats. Active manipulation of species generally will not be feasible in the region's extensive, lightly managed, natural ecosystems, though in some circumstances-such as for endangered or commercially important species-relocation to new and more suitable habitats may be desirable and feasible.
Continued research on natural ecosystems also is a necessary, integral part of adaptation responses. In many instances, our knowledge is insufficient to provide the guidance sought by managers and policymakers. Routine climatic, environmental, and ecological monitoring and prediction also are necessary.
In summary, it must be concluded that some of the region's species and ecosystems are rather vulnerable to climate change because of the likely continued increase of greenhouse gases; the likely rate of climate change; the fundamental nature of likely changes to biota and ecosystems; the large proportion of Australasia affected; the ecological isolation and fragmentation of ecosystems of the region; existing environmental stresses; and the limited available options for conscious adaptation.
Summary: The four hydrological situations of most concern to the region are drought-prone areas, flood-prone urban areas, low-lying islands, and alpine snowfields. Model simulations suggest changes of as much as ±20% in soil moisture and runoff in Australia by 2030, with considerable variation from place to place and season to season and with the possibility of an overall reduction in average runoff. Water shortages would sharpen competition among various uses of water, especially where large diversions are made for economic purposes. One study shows Australia's major Murray-Darling River system facing constraints on existing irrigation uses and/or harm to the riverine environment. More frequent high-rainfall events would enhance groundwater recharge and dam-filling events but also would increase the impacts of flooding, landslides, and erosion. A preliminary study for an urban area near Sydney showed a tenfold increase in the potential damage of the "100-year" flood under a doubled CO2 scenario. Water supplies on atolls and low-lying islands are vulnerable to saltwater intrusion of groundwater from rising sea levels and to possible rainfall reductions. Reduced snow amounts and a shorter snow season appear likely and would decrease the amenity value of the mountains and the viability of the ski industry. The glaciers of New Zealand's Southern Alps are likely to shrink further.
Adaptation options include integrated catchment management, changes to water pricing systems, water efficiency initiatives, building or rebuilding engineering structures, relocation of buildings, urban planning and management, and improved water supply measures in remote areas and low-lying islands. The financial exposure, and cost involved in potential adaptations, indicate a high vulnerability with respect to hydrology.
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