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Altered weather patterns

Braided River Status

All braided river estuaries and coastal lagoons/hapua throughout New Zealand will be affected in varying ways, depending on their location and catchments.

Description

“Since 1950, there has been 0.4 to 0.7°C warming, with more heatwaves, fewer frosts, more rain in south-west New Zealand, and less rain in north-eastern New Zealand. New Zealand is already experiencing impacts from recent climate change… These are now evident in increasing stresses on water supply and agriculture, changed natural ecosystems, reduced seasonal snow cover, and glacier shrinkage.”

IPCC 4th Assessment on climate change impacts for New Zealand and the South Pacific (2007).

Rising concentration of greenhouse gasses (GHG) in the atmosphere is changing global weather patterns, which in turn is leading to altered weather patterns in New Zealand. One of the drivers of weather is the difference in temperatures between the poles and the tropics. The poles are warming rapidly, with temperatures being recorded in Antarctica as much as 17°C above average in March 2015. These changes in temperatures alter the way global weather behaves.

Additionally, the heat in the atmosphere turbo-charges weather events, leading to ‘weather bombs’. Storms become more intense, resulting in more frequent and more intense flooding. Droughts are longer and harsher with increased evapotranspiration. Winter snow pack is declining, leading to a change in river flows.

Projected precipitation 2030-2049 (2008 modelling based on an average scenario, not a ‘high emission’ scenario.

Projected precipitation 2030-2049 (2008 modelling  on ‘average’ not  ‘high emission’ scenario) Source: NIWA

Why is it a problem for braided rivers?

  1. Higher temperatures and concurrent higher evapotranspiration
    • higher in-water temperatures particularly downstream
      • altered in-stream ecology including increase algae/periphyton blooms resulting in less food supply for braided river birds
    • loss of temperature constrained native riparian vegetation leading to
      • less suitable breeding habitat
      • more cover for predators
    • increase in temperature tolerant invasive plants leading to
      • less suitable breeding habitat
      • more cover for predatory mammals
    • possible phenological changes?
  2. Reduced average rainfall on eastern side of the Main Divide
    • increased demand to secure reliable water supply for irrigation, power generation, and consumption leading to
      • increasing demand for dams/water storage
    • for foothill-fed rivers, opportunistic invasive weeds alter braided river characteristics, leading to
      • less suitable breeding habitat
      • more cover for predatory mammals
  3. Reduced winter snowpack in the mountains
    • increased demand to secure reliable water supply for irrigation, power generation, and consumption leading to
      • increasing demand for dams/water storage
    • decreased frequency and intensity of ‘freshes’ from snowmelt leading to
      • altered in-stream ecology including increase algae/periphyton blooms resulting in less food supply for braided river birds
  4. Increased average rainfall and intensity on the western side of the Main Divide
    • Increased frequency of floods in mountain-fed rivers
      • damage to breeding sites
      • engineering works to prevent flooding, degrading braided river characteristics suitable for breeding birds
  5. Increased frequency and scale nor’west winds
    • increased fire risk
    • higher evapotranspiration
    • higher average temperatures (see 1)
Projected temperature changes 2030-2049 2008 Modelling based on an average scenario, not ‘high emission’ scenario.

Projected temperature changes 2030-2049 (2008 modelling based on ‘average’ scenario, not ‘high emission’ scenario) Source:NIWA

Conservation Activities

  • Reduction of greenhouse gasses (GHG) is required to reduce the speed at which weather is changing. Due to an escalating  feedback loop of ice melt in the Poles, the weather will not ‘return to normal’ within our lifetimes.

More information

Research papers

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