When the weather conditions at a place differ significantly from long-term expected patterns, they can present a hazard to the people, property and infrastructure located there. 

These events are often referred to as extreme weather and can vary in duration from hours to days, in the case of heavy rain and thunderstorms, to weeks, months or even years in the case of droughts.  

Please see below for a description of some of the main weather hazards that can affect Otago and how they may be influenced by climate change. Please note the ORC Natural Hazards Database Portal does not currently hold mapping for drought, wildfire, snowfall, strong wind or thunderstorm weather hazards affecting the Otago region. 

Snowfall can present a major hazard for people in Otago, particularly when deep snow builds up in densely populated coastal areas which are not regularly affected by snow. Heavy snow loads can collapse roofs and gutters and bring down power and telephone lines.

Snow can also close roads and affect transport links such as airports, rail lines and bus services. Road access across the region can be affected, particularly the alpine passes such as the Lindis and Haast, and State Highway 1 north and south of Dunedin.

Snow may fall to sea level for one to three days and form into drifts.
When snow persists for several days, frosts and widespread ice can also develop, causing dangerous conditions under foot and on our roads.
 
Climate change is expected to cause more variation in the longer-term weather conditions and patterns of a place. This may influence the frequency and intensity of snowfall events in Otago, with more snow falling at once and longer periods in between with none at all. This may have a considerable impact on industries that rely on regular snow fall for their operations, while the impacts of snow fall events may be more pronounced.

Please click here for more information on climate change in Otago.

Heavy rain and thunderstorm events can present a significant hazard for people in Otago. Heavy rain can cause rivers and streams to overtop their banks, causing major flooding in the surrounding areas. Water can also pool in areas where drainage is poor and the capacity of the ground surface to absorb excess water is lost. This can cause major water damage to property and infrastructure, make roads impassable, and pose a threat to human life where flood waters are fast and deep.

During thunderstorms, localised, short bursts rainfall can reach intensities of 25 mm and hour or more, resulting in very large amounts of rainfall over a short space of time. This can trigger rockfall and landslides alongside roads, and flash flood type hazards in the areas surrounding alluvial fans at the foot of steep stream catchments.

Thunderstorms also produce lightening which can pose a significant threat to people, property and infrastructure when it strikes the ground. Cloud to ground lightening can strike buildings, trees, people and animals, as well as trigger wildfires and cause major damage to electrical infrastructure. Thunderstorms often develop very quickly and are difficult to predict.

Climate change is expected to cause more variation in the longer-term weather conditions and patterns of a place. This may influence the frequency and intensity of heavy rain, thunderstorm and large-scale weather system events in Otago, with potentially more frequent and heavier rainfall, more destructive thunderstorms and more favourable conditions for ex-tropical cyclone systems to make their way south into Otago.

Please click here to visit the Otago Civil Defence and Emergency Management website for tips on how you can get ready for major storm events in Otago.