BAMOS
Dec 2018
6. Long-term trends 7. Conclusion
Averaging the counts across all the cities, there is a statistically
significant (to 95% confidence level) negative linear trend of
−2.3 days per decade in the annual average count of ‘nice’ days
across Australia since 1970 (see Figure 5). The dip below the
trend line in the most recent years of the annual data comes
from the cooler months of the year, mainly from fewer ‘nice’
days in northern Australia. Dividing the data by season, the
largest trend is in summer, with a negative linear trend of −8
days per decade. Looking at Australia’s major cities, Brisbane has Australia’s
‘nicest’ weather to suit an urban lifestyle, being located at just
the right latitude for warm, sunny days. The second half of
autumn is the best time of the year to experience a ‘nice’ day
somewhere around Australia, with mid-summer the least likely
time for a ‘nice’ day owing to the often-hot conditions. The long-
term trend is for fewer ‘nice’ days in Australia overall, although
warmer temperatures and shifting rainfall patterns may lead to
an increase in ‘nice’ days in some parts of southern Australia.
The linear trends for individual sites were not statistically
significant, however most cities across Australia showed
negative trends in the annual counts of ‘nice’ days.
In Australia’s south, trends in the annual count of ‘nice’ days were
small and the sign varied from city to city. In Australia’s tropical
north, trends were more consistently negative. For example,
Darwin averaged more than six ‘nice’ days per year in the 1960s,
but has been averaging less than one ‘nice’ day per year in the
most recent decade. This change is consistent with the warming
trend, which is leading to increasing frequencies of hot days.
Figure 5. Time series of the annual average count of ‘nice’ days per city for Australia (1970–2017). The dotted line is the
linear regression trend line.
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