Australian Drought Research Paper

Topic 1 - Drought

Drought is a phenomenon that has become characterizes a majority of Australia’s climate. It can be detrimental to the population of Australia especially on agricultural productivity. Within the region of drought southeastern Australia there are three main occurrences that cause drought, El Niño Southern oscillation, Indian Ocean dipole and variability and the Southern annular mode. Since drought in Australia can become so severe, the federal government has accepted drought as a feature of the climate and has emergency funding for those affected in times of ‘exceptional circumstances’ (textbook).

With Australia being termed as the driest inhabited continent in the world drought can be broadly defined as a period of time

where a particular area has received an insufficient quantity of water whether through rainfall, surface or ground water. Although the concept of drought is defined by four factor, agricultural, hydrological and socioeconomic. Meteorological explains lower than average rainfall, agricultural s inadequate soil moisture that impacts crop growth, hydrological is a deficiency in surface and subsurface water levels for example lakes and rivers water supply and socioeconomic is when the effect of drought impacts the health an wellbeing and economy of the population. Furthermore there is no distinct start or end to drought events and they can be localized or widespread among various regions.

El Nino Southern Oscillation

The El Niño southern oscillation has a major influence in causing drought occurrences in Australia.

El Niño southern oscillation involves a cycle that can occur every 2-7 years that changes the pressure gradient within the Indonesian – Australian low-pressure cell and the Southern pacific High pressure cell over the Peruvian coast.

ENSO involves three phases, Neutral, La Nina and El Nino. El Nino and its affects on Australia is the aspect of the oscillation that brings high pressure systems, cooler ocean temperatures and convection moves away from the Australian coast which all generate drought. The Neutral phase is comprised of the normal walker circulation of the atmosphere; trade winds blow westward, this produces warm surface water in the west (Indo-Australia) and cool surface water in the east (Peruvian coast). This normal cell pattern brings strong uplifts of moist air resulting in heavy seasonal rainfall off the Australian coasts. The La Nina phase is like an intensification of the walker circulation where there is increased convection and stronger trade winds over towards Australia resulting in increased

monsoons.

When El Niño is present in Australia it is accompanied with High-pressure systems are associated with subsiding warm air and less rainfall. High-pressure systems also cause less cloudy conditions (BOM; 2012), which contributes to the affects of a drought as there is too concentrated sunlight resulting in damage to crops and other plants.

During el nino, dryer winter and spring periods for victoria

Easterly trade winds sometimes reverse to westerly

This event the trade walso bring with it oceanic waters which are below average and this results in less rainfall as the water is too cold to be evaporated therefore convection is moved away from the Australian coast.

Indian Ocean Dipole

Influences winter and spring rainfall, brings rainfall to victoria when the north eastern Indian Ocean increases amounts of moisture produced into the atmosphere, this moist air can then be moved across Australia providing significant rainfall for southern Australian and victoria.

Although when there is less moist air developing over the northern Indian ocean less clouds full of precipitation is moved to southern Australia and victoria greatly impacting the rainfall for the usual time periods over winter and spring.

Just like the ENSO affects the east coast of Australia from the Pacific Ocean, the Indian Ocean dipole affects the western coast leading into southern Australia from the Indian Ocean. This weather pattern varies between positive, neutral and negative phases in a cycle similar to that of ENSO, although at the rate of every 3-8 years. (CSIRO). As mentioned, during these positive IOD events lower moisture developing over the north eastern Indian Ocean is caused by below average sea surface temperatures and similar to ENSO, this cool water causes less convection causing droughts in Australia whilst introducing floods to parts of India and East Africa. It is also believed that positive IOD events have a significant influence on extreme weather events like drought, but also events such as wildfire in southern Victoria specifically the Black Saturday bushfires in Victoria in 2009. During the negative phase, there is a presence of warmer water

over the eastern Indian Ocean, which increases rainfall over western and southern parts of Australia and the neutral phase…….

Any IOD event usually begins in the early winter months of May-June then begins to decline around August-October. During positive Indian Ocean Dipole this directly coincides which southern Australia’s wetter months, therefore subjecting these areas to below average rainfall. Furthermore the effects of Positive IOD can be exacerbated when they’re in conjunction with El Nino events over affecting the Pacific Ocean off Australia. This can cause severe drought throughout this region, as two major influences of seasonal rainfall patterns have not occurred. The Figures below show the average rainfall deciles for the winter spring period during a positive IOD event and then continue to display the average rainfall deciles for a winter spring period where Australia was under the influence of both El Nino and positive IOD. It can be seen with both weather phenomena the majority of central to eastern Australia is within the lowest 20% of average rainfall for the area.

Reducing average rainfall that can have a negative impact on agriculture within victoria

Southern annular mode

The Southern Annular Mode is the term given to the westerly wind belt that circles Antarctica and its movement North and South. This weather phenomenon dominates the middle to higher latitudes of the southern hemisphere (BOM). This circulation has a large impact on rainfall patterns present over Southern Australia; it decides factors such as cold fronts and mid latitude storm systems. Like ENSO and IOD, SAM events have a positive and negative phase. The positive phase keeps strong westerly winds in close circulation to Antarctica and the weaker westerly’s also brings high pressure systems that allow less cold fronts that are accompanied by low pressure systems and produce rainfall, away from the southern coastline and particularly from reaching inland southern Australia (BOM). Therefore as a full result, dry stable conditions are predicted during this time. The Negative phase