Western Adelaide Region Climate Change Adaptation Plan - Stage 1 - page 48

42
scenario for 2070 the most likely outcome (i.e. the 50 th percentile) is for annual rainfall to decline by about
15% (about 60-75 mm/y).
Climate models suggest that rainfall will decline more in spring than autumn. However, observational
evidence suggests that autumn-winter rainfall has changed most in recent years and that this may be
linked to climate change impacts on atmospheric circulation patterns. This pattern may continue in future.
Table 4.2: Average annual rainfall for Study Area’s meteorological stations: historical and under 2030 and
2070 climate change scenarios.
BoM
Station
1980-1999 2030 high
emissions 10th
percentile
2030 low
emissions 90th
percentile
2070 high
emissions 10 th
percentile
2070 low
emissions 90th
percentile
Adelaide Airport 451 mm 391 mm 459 mm 294 mm 475 mm
Saltworks 441 mm 383 mm 449 mm 287 mm 465 mm
North Adelaide 513 mm 445 mm 521 mm 334 mm 539 mm
Pooraka 465 mm 403 mm 473 mm 303 mm 490 mm
Seaton 466 mm 404 mm 474 mm 302 mm 491 mm
Source: Derived from Bureau of Meteorology, using climate change factors from DENR 2010.
4.7.5.3. Extreme daily rainfall
The exceedance curve for daily rainfall for Adelaide Airport meteorological station ( Figure 4.18) shows
the probability that various daily rainfall totals will be exceeded under historical conditions (based on the
full length of record). It shows that the daily rainfall total that is exceed only once each year on average
(1 y average recurrence interval; ARI) is 27 mm. The corresponding 10 and 100 y ARI daily rainfall totals
are 50 and 75 mm, respectively.
The Clausius-Clapeyron equation, which relates changes in water vapour pressure with temperature, may
be used to project the influence of climate change. The equation suggests that for each degree of global
warming, extreme daily rainfall may increase by 7% (Westra, 2011) 6, although it may not apply in every
circumstance.
The Clausius-Clapeyron equation was used to recalculate the daily rainfall exceedance curve for
Adelaide Airport meteorological station (Figure 4.18) for three emissions scenarios. Extreme daily rainfall
for the 2030 high and 2070 low emissions scenarios (50 th percentile) are similar, with 10 year ARI daily
rainfall totals of 53-55 mm, which is only slightly greater than experienced currently. Under the 2070 high
emissions (50th percentile) scenario, which is significantly greater change in temperature, the projected 10
and 100 y ARI rainfall events increase from 50 and 75 mm, respectively to 58 and 90 mm, respectively.
6 The influence of climate change on extreme rainfall conditions is quite uncertain and is the subject of considerable research effort.
The Clausius-Clapeyron equation is used here to indicate the scale of change in extreme rainfall that may occur in response to
climate change. However, rainfall projections based on this equation should not be considered to be definitive.
Changing circulation patterns in southern South Australia may mean that extreme rainfall intensity may not increase in line with the
Clausius-Clapeyron relationship. Observational evidence does not at this stage does not show any increase in annual maximum
daily rainfall.