Updated analysis as of January 07
2006 was the year of the "green drought". We can see this anecdotal reference borne out by rain records from Fred Moffett's gauge at Yoorala Street, The Gap.
At 732mm, 2006 was the third driest year in the last two and a half decades, following 1993 (697mm), 2000 (589mm), and 2002 (636mm).
Where these other dry years had some quite wet months and a lot of very dry months, 2006 was quite even. Every month had just enough rain to keep the appearance of green growth. Beneath the surface (literally) it was a different story. The land was parched and getting progressively drier. The water table was not getting recharged and we saw many mature trees dying as their roots, grown in better years, were finding no water.
Trees which should be in their prime (like 30 year old Brush Boxes) have died, especially along the ridge lines all throughout the surrounding bushland of Brisbane Forest Park, Mount Coot-tha, Diagular Range and Enoggera army land.
Other trees in marginal areas along creek have shed more large limbs than expected - under very little provocation. Small storms have brought down more than their share of large tree limbs.
2005 was very dry (761mm), and combined with 2006 the two year low (less than in several previous single years) has deepened the drought. The creeks have not had a really good flush out since 1999, when we had 1526mm.
We have only been under 800mm five times in the last 25 years, and all of these dry years have been within the last 15 years. Worse than that, four of our five driest years in the last 25 have occurred in the last seven years (since 2000). That adds up to only one thing - DROUGHT (no matter how green it looks).
The good news is that we have already had 56mm in the first four days of 2007, and it looks like more on the way.
Year ending December 31 2005
What are our wettest months? What are our driest months? What does a good year look like? What years were drought?
The one thing that stands out like the proverbial Grewia Latifolia is 1996 where the highest monthly rainfall for Yoorala St (since 1982) was recorded. That was 737 mm in May 1996. In that month, not normally noted for downpours, more rain fell than in the entire year for 1993, 2000 and 2002, and about the same for the whole year 2005.
The creek flooded that year, jet skis and surboards and canoes went skimming across waters under which were bridges, weeds, trees, and in which floated all sorts of debris from windows through to wheely bins.
Taking a long view, one can discern a pattern of mostly wet years through the 80s and 90s. Then came a period of bitter dry.
Such a sustained period of low rainfall is but a shadow of the situation faced by the major dams in the catchment for Brisbane's water supply.
Brisbane is replenished by the occasional South Easterly Blow in such conditions. Scattered showers for about three days. Here in the Enoggera catchment we are at the extreme western edge of this effect.
Further west where the Wivenhoe gets its moisture it was dry, dry, dry.
Thus we have an extreme drought affecting Brisbane even though locally, our previous year (2004) was not so bad.
This year (2005) has seen an exceptionally dry period from February to August, after which storms and rain periods have been regular and in most cases, soft on the catchment. We have had replenishing moisture without catastrophic effects.
There are rumours about that a La Nina is shaping up - meaning an early start to the monsoon and a sustained wet Summer and Autumn. But only time will tell.
Thanks to Fred Moffett for these fascinating figures -- and keep recording!