AcCLIMATise - A DAFWA project July/August 2007

The Season to Date

At the beginning of the season Esperance district was benefiting from neutral El Nino conditions and a strengthening sea surface temperature gradient in the Indian Ocean. Cumulative rainfall was tracking at about decile 7-9. Most growers sowed around the third week in May after above average falls in April and just before reasonable falls at the end of May. Since then, however, monthly falls have been below average, and the season's cumulative rainfall has retreated to decile 5 - or in Mt Madden down to decile 2.

Seasonal Outlook

The DFAWA May Growing Season Outlook is available on line at www.agric.wa.gov.au/climate. This will be updated on 13 August. The following comments are largely drawn from that Outlook.

The transition to La Niña conditions have weakened, and a weak La Niña to slightly cool conditions now looks likely. Current ENSO Sequence System (ESS) analogue years indicate that July-October rainfall for WA is likely to be average to below average.

In June, colder air from the south helped cool sea surface temperatures (SST) north of Australia and warm the SST to the west of Perth. This reversal in the SST gradient is likely to dampen moisture inflow, cloud-band activity and rainfall in the short term. However recent pressure changes suggest that this pattern could break down in the longer term.

The experimental outlook map (below) produced by DAFWA based on analogue years (1952, 1970 and 1995) with similar ESS conditions reflects this outlook - that is average to below average rainfall for July to September.



Seasonal outlooks from other agencies generally reflect this average to slightly below average rainfall prognosis. Four out of the six models indicate no clear preference for either wetter or drier conditions across July to September, while the rest indicate near average or a weak shift towards drier conditions. Caution needs to be exercised about the level of confidence to place in these predictions. The predictive value of analogue years based on ENSO modelling varies across regions, and in our region has been less reliable than elsewhere.

At the end of June, soil moisture was still maintained in this district, despite below average monthly rain over May and June. However with continuing below average rainfalls over July this level of soil moisture has fallen back. This is demonstrated in the reports from the monitored sites which follow.

Sites to be monitored for the season

Click on each site for a detailed report from that site. Return to AcCLIMATise intro