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Table 4.2: Sensitivity of natural resources to present climate and climate change

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Natural resource Key climate influence Impacts of climate change Present sensitivity to climate

Rivers

Rainfall

River flows likely to, on average, increase in the west and decrease in the east of New Zealand

More intense precipitation events would increase flooding (by 2070 this could be from no change, up to a fourfold increase in the frequency of heavy rainfall events)

Less water for irrigation in northern and eastern areas

Increased problems with water quality

Strong seasonal, interannual and interdecadal fluctuations (see the example in Box 4.1 at the end of section 4.4, on peak flows in Bay of Plenty)

Lakes

Temperature and rainfall

Lake levels likely to increase, on average, in western and central parts of New Zealand, and possibly to decrease in some eastern areas

Higher temperatures and changes in rainfall, particularly in areas such as the Rotorua Lakes, could result in a range of effects, including:

  • an increased degree of eutrophication and greater frequency of algal blooms

  • altering of lake margin habitats, including wetlands, with either increased or decreased rainfall

  • negative impacts on aquatic macrophytes, particularly native species, if lake levels fall

  • a decrease in the range of trout with increased water temperatures

  • increased ranges of pest species (eg, carp), placing even more pressure on aquatic ecosystems

Seasonal and interannual fluctuations

Wetlands

Temperature, rainfall, sea-level rise

Coastal and inland wetlands would be adversely affected by temperature increases, rainfall increases or decreases and sea-level rise

Many already under threat

Groundwater

Rainfall

Little change to groundwater recharge is expected in eastern New Zealand, but increased demand for water is likely

Some localised aquifers in northern and eastern regions could experience reduced recharge. For example, small coastal aquifers in Northland would be under threat from reduced rainfall

Seasonal fluctuations; but at present, generally stable over the longer term

Water quality

Temperature and rainfall

Reduced rainfall and increased temperatures could have significant impacts on the quality of surface water resources in northern and eastern New Zealand

Lower stream flows or lake levels would increase nutrient loading and lead to increased eutrophication

Most sensitive during summer months and in drier years

Drainage

Rainfall

Increased frequency of intense rainfall events could occur throughout New Zealand, which would lead to increased surface flooding and stormwater flows, and increased frequency of groundwater level changes

Natural year-to-year variation in the location and size of heavy rainfall events

Water availability

Rainfall

Decreases in rainfall, which are most likely in the north and east of New Zealand, coupled with increased demand, would lead to decreased security of water supply

Dry summers, or extended droughts

Erosion

Rainfall and wind

Increased rainfall in the west, and more intense rainfall events throughout New Zealand, could lead to increased soil erosion, including landslides

Intense rainfall events can arise with subtropical lows, and localised low pressure cells

Biodiversity

Temperature, rainfall, wind

Increased temperature, reduced rainfall and more frequent drying westerly winds (possible in the east) would lead to changes in distribution and composition of native forest ecosystems throughout New Zealand

Most vulnerable will be fragmented native forests in the north and east of New Zealand

An increased biosecurity risk, with invasive temperate and subtropical species, would also have negative impacts on native flora and fauna

Drought can have a severe impact, eg, some native vegetation was adversely affected in Hawke’s Bay with the 1997/98 El Niño drought

Biosecurity

Temperature and rainfall

Even small increases in temperature will significantly increase the incidence of pest outbreaks in New Zealand, particularly in the North Island and the north of the South Island

Both existing and potential new plant and animal pests could become established more widely, even with a slight increase in temperature

Pest outbreaks can be triggered by specific weather events, or from steadily changing conditions, eg, spread of Tasmanian grass grub in Hawke’s Bay was triggered by the warmer, drier conditions in the late 1980s and early 1990s

Coastal areas

Sea-level rise, storm frequency and intensity, wave climate, sediment supply

Effects of sea-level rise and other changes will vary regionally and locally

Coastal erosion is likely to be accelerated where it is already occurring and erosion may become a problem over time in coastal areas that are presently either stable or are advancing

Short- and medium-term fluctuations in sea levels (ie, up to about 30 years) are dominated by ENSO and IPO variations

Air

Temperature, rainfall, wind

Increased temperatures in Auckland might increase photochemical smog

Fewer cold nights may reduce particulate smog problems in winter in affected towns and cities

 

Natural hazards

Temperature, rainfall, wind

The general indications are that New Zealand could experience more climatic extremes in the future. These could include:

  • more intense rainfall events, and associated flooding, in most parts of the country

  • more frequent and/or intense droughts in the east

  • more damaging windstorms

  • more heat waves

  • increased fire risk in drier eastern areas

There have been more frequent and intense El Niño events in recent decades, possibly associated with the IPO. The worldwide cost of extreme weather damage has increased owing to a mixture of climatic, economic and social factors