Extreme Rainfall Trends In Australia
By Paul Homewood
As promised, a look at the Australian climate extremes graphs for precipitation, as presented by the BOM.
Most of the extreme rainfall graphs show a similar pattern, so I have picked this one, defined as “Annual total precipitation when daily precipitation > 99th percentile”.
This, in theory, takes account of varying rainfall expectations from region to region, as the BOM explain:
Extreme climate events such as heat waves, cold snaps, floods and dry spells have significant impacts on society. To examine whether such extremes have changed over time a variety of extreme climate indices can be defined, such as the number of days per year which exceed, or fail to exceed, fixed thresholds. However, since people tend to adapt to their local climate, a threshold considered extreme in one part of Australia could be considered quite normal in another. To overcome this problem, thresholds based on percentile values can also be defined.
What the data shows is that extreme rainfall has not become more common or intense in recent years. Indeed, the opposite looks to be the case.
This may be slightly surprising, given that total rainfall in Australia has noticeably increased since prior to 1970.
At the other end of the scale, we have the average number of consecutive dry days, the maximum number of consecutive days with daily precipitation < 1 mm.
We can see that this index has been running at record low levels in the last decade or so.
To sum up:
1) Rainfall is not becoming more extreme.
2) Dry spells are becoming less common.
We already seen that the extreme temperature graphs show that very hot days are not getting hotter or more frequent in Australia. Instead, it is the very cold ones that have become less common.
In other words, climate is not getting more extreme in Australia. If anything, the reverse is true.
We are often told that global warming is leading to more extreme weather. Not for the first time, the facts tell a different story.