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.

Climate changes will affect home design. When designing for climate change, designers will need to consider changes to all of the following climatic conditions.

Temperature

Projections for average temperature rises by the Ministry for the Environment are that New Zealand temperatures are expected to rise by 0.6–0.7°C by 2030 and by 1.6–2.0°C by 2080. The strongest warming is likely to be experienced in winter, and warming may be greater in eastern and northern parts of the country.

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

If these changes occur, they may affect thermal comfort and the demand for cooling inside homes. If there is also an associated rise in humidity, there may potentially be an increase in mould and fungi growth that could in turn result in a rise in health issues.

Rainfall

The Ministry for the Environment also gives a mid-range rainfall projection for New Zealand of -5 to +5% increase by 2030 and -10 to +15% by 2080.

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). This means that the difference between current rainfall levels between east and western areas will increase.

Extreme rainfall is expected to become more common, particularly in the south and west. This will put more pressure on stormwater and sewer systems and on roof drainage. The risk of flooding could increase, and properties in low-lying areas are likely to be at risk.

Summer rainfall is expected to reduce, which will put pressure on urban water supplies. More droughts are expected in areas that are already currently drought-prone.

Higher temperatures, lower summer rainfall, increased winter rainfall, increased evapotranspiration 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 buildings 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 (for example, plastic, rubber, wood lignin).

The effects of climate change on solar radiation through changes in cloud levels or sunshine hours are uncertain.

Wind

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

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

Rising sea levels

The Ministry for the Environment recommends planning for at least an 800 mm rise in sea level by the end of the 21st century relative to the 1980–1999 average.

Western areas are expected to experience heavy swells more frequently. It is also considered that there will be an increased intensity of severe storms and a rise in storm surge levels. Coastal defences are likely to be over-topped by waves and high tides more frequently, causing increased rates of coastal erosion and inundation, which could have catastrophic consequences for buildings in coastal locations.

Fire risk

The fire risk is expected to increase significantly by the middle of the 21st century in eastern locations because of reduced summer rainfall and increasingly dry vegetation.

Insect pests

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

Impact of emissions charges

If either a carbon charge or an emissions trading system are introduced, they are likely to result in an increased cost of electricity and other forms of energy.

Building materials costs are also likely to increase, with the greatest increases being in the materials with the highest production costs. This means that the percentage cost increase is likely to be least for timber products with relatively higher increases for cement, steel and aluminium.

Increases in energy costs will depend on the source of the energy. Prices for coal and gasgenerated electricity are likely to increase. As prices rise, however, the rewards for energy efficiency will be comparatively greater, and renewable energy sources such as wind and photovoltaic cells will become more economic.

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 require that increased structure, durability and weathertightness issues are met in the face of more extreme weather events.

The threat of rising sea levels and increased numbers of storms and storm surges mean the local governments are likely to implement restrictions on coastal developments and to refuse consent applications for alterations and additions to existing building in low-lying coastal regions.