Increased temperatures will lead to a reduced fraction of precipitation falling
as snow, higher snowlines, earlier spring snowmelt, and a shorter snow season
in Australia (Whetton et al., 1996c) and New Zealand (Garr and Fitzharris, 1994;
Fitzharris and Garr, 1996). Figure 4-3 shows the results
of a simulation of the progressive shortening of the snow season at Mt. Bogong-one
of Australia's higher-altitude snow areas-over the first half of the next century,
based on the CSIRO (1992) scenarios. Greater ablation of New Zealand's Southern
Alps' glaciers can be expected, and the volumes of glaciers and total snowpack
may decrease, depending on precipitation changes (note that the new scenarios
for New Zealand referred to in Section 4.2.3 may result
in increased precipitation in the Southern Alps). However, it has been estimated
that even with a 10% increase in precipitation, a 2�C temperature rise would
cause a 20% reduction in the Southern Alps' snow amount (IPCC 1996, WG II, Section
7.4.1). Reductions in relative snow amounts would change the seasonality of
runoff by increasing winter runoff and decreasing spring runoff (IPCC 1996,
WG II, Section 10.3.5). This would reduce spring flood risks and provide more
seasonally smooth hydroelectricity generation (IPCC 1996, WG II, Section 7.5.2).
Any changes in atmospheric circulation patterns also would cause changed seasonality
of rainfall and river flows, but there is less certainty about the nature of
these changes.
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| Figure 4-3: Simulation of the future decrease in the length of the snow season at Mt. Bogong in southeastern Australia, for best-case (solid) and worst-case (dashed) climate change scenarios. An indication of year-to-year variability is provided by superimposing the year-to-year climate anomalies for 1966-85. Further details can be found in Whetton et al. (1996c). |
Under the scenario of more frequent extreme rainfalls, hydroelectricity systems
would need to be managed more conservatively, to avoid the risk of overtopping
of dams in floods and running out of water during droughts. Increased sediment
transport would accelerate the reduction of the storage capacities of hydro
lakes. Increases in the temperatures of rivers would reduce the rivers' capacity
to cool thermal generating plants, with increased difficulty in meeting regulatory
constraints on downstream river temperature (IPCC 1996, WG II, Section 14.3.3).
Decreased snow amounts would most likely reduce the amenity value of mountain landscapes for the local population and tourists and reduce the viability of the region's ski industry, whose options for relocation are very limited-by low altitude in Australia and by rugged terrain and conservation estate regulations in New Zealand (IPCC 1996, WG II, Section 7.5.5; Whetton et al., 1996c).
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