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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. The quote below was from a 2007 synthesis report. It’s dated, but current events underscore the rapid changes now taking place.

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 (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. In Siberia in February 2018, temperatures reached 35°C above average. These changes in temperatures alter the way global weather behaves, sometimes leading to unexpected ourtcomes, for example the ‘wobble’ in the polar vortex leading to massive temperature swings in Nortth America January 2019.

Heat in the atmosphere turbo-charges atmospheric weather events, leading to ‘weather bombs’. Storms become more intense, resulting in more frequent and more intense flooding. Droughts are outcomes and harsher with increased evapotranspiration. Winter snow pack and glacial mass in New Zealand is decreasing rapidly, leading to a change in river flows.

The impacts of higher temperatures also affect the oceanic food web, and with it, the availability of food for river birds, especially during winter. What has now become known as a ‘marine heatwave’, was responsible for killing millions of fish, marine mammals, and seabirds in 2017. Marine heatwaves are predicted to become the new normal.

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?

Higher temperatures and concurrent higher evapotranspiration

  • Altered in-stream ecology including increase algae/periphyton blooms resulting in less food supply for braided river birds
  • Higher in-water temperatures particularly downstream
  • 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 predators
  • Phenological changes (already being seen in the ocean)
    • Reduced availability of food

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:
    • More cover for predators
    • Less suitable breeding habitat

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

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

Increased frequency and scale nor’west winds

  • Increased fire risk
  • Higher evapotranspiration
  • Higher average temperatures (see maps below)
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

Projected impacts for New Zealand (NIWA)

Research papers

As with rising sea levels, this area of research is moving at such a rapid pace, we have opted not to include specific links here. If you are looking for the latest peer-reviewed research on the topic, you might like to start with the journal Nature Climate Change.

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