Passive Design

The National Institute of Water and Atmospheric Research (NIWA) has warned that the biggest effects may be from more extreme and more frequent weather events such as floods, droughts and storms, rather than changes in average weather conditions.

These changes will affect home design – they may have to withstand heavier rainfall, or be designed for temperatures that are warmer than now. Climate change also has other potential effects – for example, on transport and insurance costs.

The UN’s Intergovernmental Panel on Climate Change has predicted that the effects will be very long-lasting. Even if carbon dioxide emissions are stabilised soon, global temperatures and sea levels will continue to rise for hundreds or thousands of years.

Temperatures

According to NIWA, temperatures are expected to rise by 0.3-0.9°C by 2030 and by 0.6-2.7°C by 2070. The strongest warming will be felt in winter, and slightly more warming will be felt in eastern and northern parts of the country.

An increase in the number of days above 25°C is expected, particularly at already warm northern locations.

These changes will affect thermal comfort and the demand for cooling inside homes. If associated with a rise in humidity there could also be an to increased mould growth and potentially other health problems.

Rainfall, flooding and droughts

Rainfall is expected to increase in southern and western areas (Taranaki, Manawatu-Wanganui, West Coast, Otago and Southland) and decrease in northern and eastern areas (Hawke’s Bay, Gisborne, eastern Marlborough and eastern Canterbury).

Extreme rainfall is expected to become more common, especially in the south and west. The number of extreme rainfall events could increase twofold by 2030 and fourfold by 2070, placing more pressure on stormwater and sewer systems, and on roof drainage. The risk of flooding is likely to increase, and some properties may become uninsurable.

Summer rainfall is expected to reduce, which is likely to place pressure on urban water supplies. More droughts are expected in areas that are currently drought prone.

Subsidence risk

Higher temperatures, lower summer rainfall, increased winter rainfall, increased evapo-transpiration, and changes to water-table levels will all change seasonal patterns of soil wetting/drying. This could increase the risk of subsidence, particularly for building foundations on clay soil or for homes adjacent to banks or cliffs.

Solar radiation and UV intensity

UV intensity is expected to increase until 2015 and later gradually decrease by about 6-7% by 2030, and be 10% lower than current levels by 2070. UV radiation is currently a major cause of polymer degradation (e.g. plastic, rubber, wood lignin).

The effects of climate change on solar radiation (through changes in cloudiness or sunshine hours) are uncertain.

Wind and storms

The westerly wind flow across New Zealand is expected to increase, and it’s likely there will be more strong winds. According to one projection, the frequency of winds of 30m/s or more might double.

The number of storms and tropical cyclones could increase – though projections are uncertain. One scenario is that the number of tropical cyclones reaching New Zealand might reduce, but those that do get here may have greater impact.

Sea levels

New Zealand sea levels are expected to 40-240 mm higher by 2030 and 100-600 mm higher by 2070. Western areas are expected to experience heavy swells more often. This will cause increased rates of coastal erosion, with catastrophic consequences for buildings in vulnerable locations.

Fire risk

The fire risk is expected to increase significantly (up to 50%) in some eastern locations by the middle to end of this century because of reduced summer rainfall and therefore increasingly dry vegetation.

Termites and other pests

Termites and infection-bearing pests such as mosquitoes might become established more readily as a result of warmer climates (though research suggests that current quarantine and timber treatment practices will be enough to keep termites away).

Changes to building/planning rules

Climate change is likely to affect building and urban planning requirements as the government and local councils seek greater energy efficiency from buildings and seek to ensure they meet structure, durability and weathertightness requirements in the face of more extreme weather events.

Impact of emissions charges

Any carbon charge or emissions trading system that’s introduced will add to the cost of electricity, building materials, and fuel.

For materials, the percentage increase will probably be least for timber products, more for cement, much more for steel, and more still for aluminium.

Increases in energy costs will depend on the source of the energy. Prices for coal and gas-generated electricity could increase dramatically. As prices rise, the rewards for energy efficiency will be comparatively greater, and renewable energy sources such as wind and photovoltaic cells will become more economic.

Increased insurance costs

If increased rainfall or sea level rise leads to increases in flooding or storm damage, insurance premiums are likely to rise. In the worst case, insurance cover could be denied.

Because insurance is a global industry, effects of climate change in other parts of the world could raise premiums in New Zealand.