La Nina ENSO event - high likelihood of a wet summer

UPDATED ADVICE -

The Bureau of Meteorology has issued an update indicating that we are currently at a Mature La Nina Event approaching peak strength.

What is La Nina?

Australia's climate is driven by cycles in ocean temperatures, currents and trade winds. From Australia’s west, the Indian Ocean Dipole strongly influences monsoonal rains and in the east coast, the Pacific Ocean is subject to the El Nino Southern Oscillation (ENSO). ENSO are massive ocean and air currents that rotate across the entire Pacific Ocean.

During an El Nino event they rotate in an anti-clockwise direction, driving warm water and hot dry air across to the east coast, causing hot and dry summers, and warm dry winters (i.e. drought and fire).

During a La Nina event, they rotate in a clockwise direction, bringing cool water and cold, wet air to the east coast. This drives wetter weather, high snowfall in winter, and flooding in summer.

The Bureau indicates that we are currently experiencing a “mature” La Nina year. The wet season has started with heavy December rainfall and it is likely that this pattern may continue through summer. This signals a high likelihood of an ongoing wet summer, with heavy rainfall and flooding.

How do we prepare?

Ensure there are plans in place for heavy rain and wet weather on any existing or proposed construction/development or maintenance projects and advise staff, contractors and development industry contacts accordingly.

Pre-prepare site-based wet weather response plans that allow a scalable response to rain events. IECA guidelines should be strictly followed to ensure ESC plans deliver a best practice approach to minimising site erosion.

Construction Site Managers should pay attention to the following:

  • be aware of the need to constantly manage construction site ESC controls in preparedness for weather events
  • ensure that sediment control dams are flocked, tested and emptied after each event
  • undertake the installation and ongoing maintenance and repair of sediment control fences as well as the application of polymers to batters and vulnerable areas
  • implement clean water diversion drainage, utilise rock checks to slow flow, undertake installation of bunds etc. good site drainage for disturbed areas and groundcover treatments implemented on exposed soils or stockpiles are essential to reduce sediment mobilisation off site
  • on sites greater than 2500m2 High Efficiency Sediment Basins must be implemented as stipulated in legislation.