Natural Hazards
The Southland region is at risk from a number of natural hazards which have the potential to cause property damage, loss of life or injury.
Avalanches
Avalanches typically occur in mountainous terrain and are primarily composed of flowing snow. They only occur in a standing snow pack and are always caused by an external stress on the pack. It is difficult to predict with absolute certainty when an avalanche will be triggered. Avalanches are among the most serious hazards to life and property, with their destructive capability resulting from their potential to carry an enormous mass of snow over large distances at considerable speed.
Avalanches are classified by their morphological characteristics, and are rated by either their destructive potential, or the mass of the downward flowing snow. Avalanche size, mass, and destructive potential are rated on a logarithmic scale, in New Zealand this scale is made up of five categories; low, moderate, considerable, high and extreme.
To keep the Milford Road safe and open as much as possible during the avalanche season (June to November), the New Zealand Transport Agency contracts a specialist avalanche team to conduct a control programme using high-tech equipment to predict and manage avalanches. A crucial part of the programme is controlling the avalanche hazard by either not allowing traffic to stop inside the avalanche area or closing the road and using controlled explosives to release avalanches before they occur naturally.
Biological Hazards
There are a large range of biological hazards that if not controlled or avoided, could cause significant loss of life or severely affect New Zealand's economy, agricultural and fishery industries, health (human & animal), and infrastructure (e.g. water supply and treatment networks). Due to our economic dependence on horticultural, agricultural and forestry industries, and limited historical exposure to disease, New Zealand is very susceptible to biological hazards.
Climate Change
Climate changes have occurred naturally in the past, and some regional changes have been significant. But globally, our climate has been relatively stable for the past 10,000 years. Human activity is increasing the natural level of greenhouse gases in the atmosphere causing Earth to warm up and the climate to change. If the world does not take action to reduce greenhouse gas emissions, the global average temperature is very likely to change more rapidly during the 21st century than during any natural variations over the past 10,000 years.
Climate change is not just rising temperatures - Under climate change New Zealand can also expect to see changes in wind patterns, storm tracks, the occurrence of droughts and frosts, and the frequency of heavy rainfall events. The impacts of climate change in New Zealand will become more pronounced as time goes on.
These changes will result in both positive and negative effects. For example:
- agricultural productivity is expected to increase in some areas but there is the risk of drought and spreading pests and diseases. It is likely that there would be costs associated with changing land-use activities to suit a new climate
- people are likely to enjoy the benefits of warmer winters with fewer frosts, but hotter summers will bring increased risks of heat stress and subtropical diseases
- forests and vegetation may grow faster, but native ecosystems could be invaded by exotic species
- drier conditions in some areas are likely to be coupled with the risk of more frequent extreme events such as floods, droughts and storms
- rising sea levels will increase the risk of erosion and saltwater intrusion, increasing the need for coastal protection
- snowlines and glaciers are expected to retreat and change water flows in major South Island rivers.
Coastal Erosion
Coastal erosion is the wearing away of the coastline usually associated with the removal of sand from a beach to deeper water offshore or alongshore into inlets, tidal shoals and bays. Coastlines constantly move, building up and eroding in response to waves, winds, storms and relative sea level rise. The effect of climate change (rising sea levels, increased severity and possibly the frequency of harsh storms) may exacerbate coastal erosion. Since the height of the land and the sea are changing, we use "relative sea level rise" to describe the rise of the ocean compared to the height of land in a particular location.
Coastal erosion and flooding can cause significant problems if people build too close to the coast. Coastal erosion is generally occurring in Southland estuaries and harbours as extensively as it is on the open coast. In some areas e.g. Colac Bay and Halfmoon Bay, the issue is becoming increasingly significant.
Drought
Southland has abundant water resources in snowfields, groundwater aquifers, rivers and lakes but despite this the region is facing growing challenges in managing its water resources. Agriculture continues to increase demand for water, and water supplies are not always in the right place at the right time.
A drought can be defined as an:
- 'Agricultural drought' where there is soil moisture deficit which impacts on agricultural and horticultural industries, and / or
- 'Water supply drought' which results in a water supply shortage
Drought events are one of New Zealand's most damaging and perhaps the most costly natural hazards. Droughts are a natural part of climate variability in Southland and have a significant impact on agricultural production, particular in Northern Southland and the Te Anau Basin. Droughts can have in a major impact on property, livelihoods and society in general. Dry periods are most common from December to March.
Impacts of drought include: crop failure and lack of stock feed, lower production, economic loss locally and regionally (generally a lag effect), poor stock condition and lower reproductive performance, psychological and social on farming communities, water shortages leading to restrictions and irrigation limitations, increased numbers and severity of rural fires.
The 2003-04 drought event, although of relatively limited duration, was calculated to have taken $63 to $72 million out of the regional economy.
Earthquakes
Southland lies adjacent to the boundary of the Pacific and Australian tectonic plates. The movement of the sub ducting Australian plate and the overlying Pacific plate together with movement along the fault line are the source of frequent earthquakes in Fiordland. The Alpine Fault, one of the world’s major active faults, has a predicted ~35 per cent likelihood of strong movement within the next 50 years. This would cause catastrophic earthquake damage along the fault and the severity of the shaking and damage would be felt to varying degrees across Southland.
Southland's most significant recent earthquake activity occurred 100 km north-west of Tuatapere on the 15 July 2009 and had a magnitude of 7.8 It must be noted this earthquake did not originate from the Alpine Fault. Fortunately because of the remote location and minimal built and social environments in this area the impact on the community was minimal.
Read more information on Earthquakes
Fire
Urban Fire
Every year Southland has on average 2,100 incidents per year that require response from the New Zealand Fire Service, these include a wide range of events e.g. Fires Relating to Structures, Mobile Property Fires, Vegetation Fires, Chemical, Flammable Liquid or Gas Fires, Miscellaneous Fires, Hazardous Emergencies, Overpressure, Rupture, Explosives, Over Heating, Rescue, Emergency Medical Calls , Medical/Assist Ambulance, Special Service Calls, Natural Disasters, Good Intent Calls, False Alarms.
Injuries to the Southland public from fire are on average 16 per year. Fatalities from fire over the last five years are on average of one per year, with no multiple fatalities from fire in the last five years.
Wildfires
Even though Southland typically has high rainfall levels wild fire is still a real risk. On average Southland experiences one large wild fire every summer and these fires cost between $500,000 - $100,000,000.
Things that increase the risk of wild fire are:
Human Error
- Leaving a burn-off or campfire unattended or not properly extinguishing them.
- Not recognising the level of risk involved with fire (e.g. too close to other vegetation, don't predict the weather changing).
- Underestimating the speed that a fire can spread.
- Poor machinery maintenance that can lead to emission of sparks or heat build-up causing combustion.
Environment
- Periods of dry weather.
- Wind, particularly warm north-westerlies.
- Large areas of continuous fuels such as native or exotic forests, peat soils.
- Burning large deep burning materials such as logs and peat.
You can obtain more material on the http://www.southernruralfire.org.nz website or by calling 0800 773 363 on fire bans and how to obtain fire permits.
Flooding
River/stream flooding as a result of sustained or short duration-high intensity rainfall can have a significant effect both directly and indirectly on a large part of the region. With four major river systems running through the region, many of them close to or passing through highly populated areas, flooding has long been recognised as a significant hazard. A substantial amount of work has been undertaken over the last century to both mitigate and monitor this hazard. Timely and effective flood warning is an integral component of emergency management arrangements for Southland communities at risk from flooding.
Some flooding events of note over the previous fifty years in Southland include but are not limited to; April 1968, Sept 1972, Oct 1978, Jan 1980, Jan 1984, Nov 1999, April 2010.
Frost
Frost is the formation of ice crystals relatively close to the ground on solid surfaces and occurs when air temperatures fall below freezing and the water vapour in the air solidifies as ice crystals. The size of the ice crystals depends on the time, temperature, and the amount of water vapour available.
Southland experiences the majority of its frosts between May and September, when seasonal temperatures fluctuate most.
Frost damage can be detrimental to a variety of different crops because water inside the cells of a plant can freeze, breaking the cell wall and destroying the integrity the plant.
The heaving of soil produced by frosts can cause structural damage, in the form of cracks, on roadways, buildings and foundations. Road, rail and air transport can also be hindered by freezing conditions.
Frosts are frequent inland during winter - Gore averages 114 each year. In coastal regions they are less common and less severe (Invercargill averages 94).
Snow in July 1996 was followed by ten consecutive frosts and was labelled the 'big freeze' and caused many frozen/burst pipes and tree deaths. The -14.2oC frost on the 3 July 1996 was the coldest on record since 1910.
High Winds
Southland's latitude of between 46 and 47 degrees south and an absence of shelter from the unsettled weather that moves over the sea from the west, south-west and south, place it within the zone for strong air movement or winds. Wind is the movement of the air or atmosphere that surrounds the earth when it warms up or cools down. Winds move moisture and heat around the world and also generate much of the weather. Winds are often referred to according to strength and direction. Wind speed is measured by anemometers and reported using the Beaufort wind force scale. There are general terms that differentiate winds of different average speeds such as a breeze, a gale, a storm, tornado, or a hurricane. Within the Beaufort scale, gale-force winds are between 28 knots (52 kilometres per hour) and 55 knots (102 kph), a storm has winds of 56 knots (104 kph) to 63 knots (117 kph).
With an average of 98 windy days per year, Invercargill is New Zealand’s second windiest city after Wellington. Examples of wind events include; 143 kph wind gusts on 9 June 1993 and 16 May 1994, August 2000 a week of strong easterlies at Oban, September 2006 record winds at Athol, 184 kph wind gust at Stewart Island on 4 November 2009. High winds can cause damage to buildings, trees/vegetation and electricity lines as well as accelerate erosion. It can also have a consequential effect for services and infrastructure supporting telecommunications, transport, water and sewage collection and treatment.
Landslides
Erosion and slope failure is not uncommon in Southland. Land instability is often made worse by human activities. For more information see the section on Coastal Erosion.
Snow
Winter snowfalls are common above 1000 metres in the Southern Alps. Southland's distance from the equator makes its weather conditions cooler than other parts of New Zealand. Snowflakes are formed when water vapour changes directly to ice without becoming a liquid. Snowflakes are made of ice crystals which form around tiny bits of dirt carried into the atmosphere by the wind, as the ice crystals grow they become heavier resulting in snow.
Snowfall often arises from slow moving deep depressions embedded in cold south-westerly, or south-easterly airstreams, the higher coastal land in western and eastern Southland is more vulnerable than elsewhere with snow occasionally occurring at sea level. Snow generated by southerly airstreams is relatively light, dry, snow whereas snow generated from warm, moist airstreams from the north and pushed up over colder, denser airstreams from the south is wetter, heavier and thicker.
The effects of snow depend on depth, weight and persistence but can impact on electricity and telecommunication delivery, road, rail and air transport, farm animal welfare and feed, forestry plantations and building structures.
Although historical snow records are incomplete and accurate measurements are lacking, it would appear from local newspapers that in July and August 1939 widespread and very deep snow fell around Southland that took six weeks to clear – northern, at least 0.5 metres with drifts up to two metres; coastal (including Invercargill) and eastern, up to 150mm. In September 2010, Southland witnessed a severe six-day severe storm that swept across a coastal belt from Colac Bay through Invercargill, the Catlins, Owaka and Clinton dumping heavy, wet, snow that caused structural damage to some buildings and massive stock losses. Road, rail and air transport can be hindered by lying snow.
Storm Surge / Tidal Effects
Storm surge is the name given to the elevation of the sea above predicted levels by wind, low barometric pressures or both. When surges coincide with high spring tides, the sea may spread out over land or stop banks adjoining the coast or tidal rivers. Some stop banks on rivers e.g. the Waihopai River next to Prestonville, Gladstone, Avenal and Collingwood, more frequently protect areas from marine inundation than riverine inundation. While in any one storm surge event sea levels are generally elevated, there are significant differences from place to place, most probably because of wind direction. The most obvious areas at risk of marine inundation are those low-lying areas of former estuary and estuary fringe that have been reclaimed through the construction of barriers. Generally, these areas have not been filled and they remain at their natural level. Less obvious are areas of low lying land, both filled and natural, that border harbour, estuarine or tidal waters.
Tsunami
Tsunami may be tens of metres in height in shallow water, however most tsunami are less than 1m in height at the shore. Historical information suggests that the most likely hazardous tsunami events to Southland are likely to be caused by earthquakes off the west coast of Peru or in the Puysegur Subduction Zone, off the south-west coast of Fiordland.
