5.3.1. Water Resources
Figure TS-7: Percentage change in average annual total Australian
wheat yield for CO2 (levels of 700 ppm) and a range of changes
in temperature and rainfall: a) current planting dates, and b) optimal planting
dates. Yield response is shown for rainfall changes of +20% (white), 0 (light
blue), and -20% (dark blue), for warmings of 0-4ºC. |
Water resources already are stressed in some
areas and therefore are highly vulnerable, especially with respect to salinization
(parts of Australia) and competition for water supply between agriculture, power
generation, urban areas, and environmental flows (high confidence). Increased
evaporation and possible decreases in rainfall in many areas would adversely
affect water supply, agriculture, and the survival and reproduction of key species
in parts of Australia and New Zealand (medium confidence). [12.3.1,
12.3.2,
12.4.6,
12.5.2,
12.5.3,
12.5.6]
5.3.2. Ecosystems
A warming of 1°C would threaten the survival of species that currently
are growing near the upper limit of their temperature range, notably in
marginal alpine regions and in the southwest of Western Australia. Species that
are unable to migrate or relocate because of land clearing, soil differences,
or topography could become endangered or extinct. Other Australian ecosystems
that are particularly vulnerable include coral reefs and arid and semi-arid
habitats. Freshwater wetlands in coastal zones in Australia and New Zealand
are vulnerable, and some New Zealand ecosystems are vulnerable to accelerated
spread of weeds. [12.4.2,
12.4.3,
12.4.4,
12.4.5,
12.4.7]
5.3.3. Food Production
Agricultural activities are particularly vulnerable to regional reductions
in rainfall in southwest and inland Australia (medium confidence). Drought
frequency and consequent stresses on agriculture are likely to increase in parts
of Australia and New Zealand as a result of higher temperatures and El Niño
changes (medium confidence). Enhanced plant growth and water-use efficiency
(WUE) resulting from CO2 increases may provide initial benefits that
offset any negative impacts from climate change (medium confidence), although
the balance is expected to become negative with warmings in excess of 2-4°C
and associated rainfall changes (medium confidence). This is illustrated in
Figure TS-7 for wheat production in Australia, for a range
of climate change scenarios. Reliance on exports of agricultural and forest
products makes the region very sensitive to changes in production and commodity
prices that are induced by changes in climate elsewhere. [12.5.2,
12.5.3,
12.5.6,
12.5.9,
12.8.7]
Australian and New Zealand fisheries are influenced by the extent and location
of nutrient upwellings governed by prevailing winds and boundary currents. In
addition, ENSO influences recruitment of some fish species and the incidence
of toxic algal blooms. [12.5.5]
5.3.4. Settlements, Industry, and Human Health
Marked trends toward greater population and investment in exposed regions
are increasing vulnerability to tropical cyclones and storm surges. Thus,
projected increases in tropical cyclone intensity and possible changes in their
location-specific frequency, along with sea-level rise, would have major impacts -- notably,
increased storm-surge heights for a given return period (medium to high confidence).
Increased frequency of high-intensity rainfall would increase flood damages
to settlements and infrastructure (medium confidence). [12.1.5.1,
12.1.5.3,
12.6.1,
12.6.4]
There is high confidence that projected climate changes will enhance the spread
of some disease vectors, thereby increasing the potential for disease outbreaks
such as mosquito-borne Ross River virus and Murray Valley encephalitis, despite
existing biosecurity and health services. [12.7.1]
5.3.5. Key Adaptation Options
Key adaptation options include improved WUE and effective trading mechanisms
for water; more appropriate land-use policies; provision of climate information
and seasonal forecasts to land users to help them manage for climate variability
and change; improved crop cultivars; revised engineering standards and zoning
for infrastructure development; and improved biosecurity and health services.
However, many natural ecosystems in Australia and New Zealand have only a limited
capacity to adapt, and many managed systems will face limits on adaptation imposed
by cost, acceptability, and other factors. [12.3.2,
12.3.3,
12.5.6,
12.7.4,
12.8.4, 12.8.5]
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