Auckland is vulnerable to the effects of different types of drought that could have severe implications on people, agriculture and the economy. Unlike most natural hazards, the onset of drought can be slow and go unrecognised. It usually occurs from a lack of precipitation, commonly rain, over a long period. In Auckland, these conditions are more likely to occur under El Niño-dominated weather conditions like the summer of 1997-1998 when our region experienced water shortages. In general, two main types of drought can affect Auckland. They are agricultural drought or hydrological drought.
Crops, including pasture, rely on moisture within the soil to survive. During an agricultural drought, soil moisture becomes so low that plants can no longer grow and start to die. As soil moisture decreases, plants become stressed and if the drought is prolonged, they will die. An agricultural drought ends when adequate amounts of rain restore soil moisture levels.
The effects of an agricultural drought in Auckland can include:
- agricultural productivity being reduced because of less breeding sheep and cattle
- significant economic losses for the horticultural sector
- considerable increases in the risk of fire resulting in the loss of crops.
A hydrological drought refers to a significant reduction in the amount of water available in rivers, lakes and groundwater (the hydrological system). This type of drought occurs when rainfall is well below expected levels in any large catchment area for an extended period. Hydrological droughts can result in water supply shortages.
In Auckland, the last most notable hydrological drought was in 1994. Advertisements promoting water conservation began that January. By late February, formal water restrictions were imposed to try to preserve water levels. Water supply levels continued to fall in the following months with a total ban on the use of water sprinklers enforced in mid-April. The drought continued until September when Auckland received more than double the normal rainfall for that month. Using rainfall data, subsequent investigations indicated that there is a 4 per cent chance of this type of drought occurring in any given year - a one in 25 year return period.
As a result of this drought and a dry summer in 1997-1998, Auckland’s water supply was redesigned in 2002 to cope with a hydrological drought with a 0.5 per cent chance of occurring in any given year (one in 200 year return period).
Some of the severe impacts of a drought include:
- Damage to plants and animals, wildlife habitat, and air and water quality.
- Forest and range fires leading to a reduced landscape quality.
- Loss of biodiversity and soil erosion.
- Public safety and health.
- Conflicts between water users.
- Inequities in the distribution of impacts and drought relief.
- Economic impacts occur in agriculture and related sectors.
- Losses in yields in both crop and livestock production.
- Insect infestations, plant disease, and wind erosion.
- Increase in the number of forest and range fires.
- Reduced income for farmers and retailers and others who provide goods and services to farmers.
- Increased prices for food, energy and other products as supplies are reduced.
Visit the NIWA website for information on drought in New Zealand.