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New Zealand summers are getting hotter – and humans aren’t the only ones feeling the effects

New Zealand summers are getting hotter – and humans aren’t the only ones feeling the effects

bull kelp clinging to rocks at beach

It’s not a mirage, our summers are getting hotter on average and we are experiencing more extremely hot days. News from NIWA that 2021 was New Zealand’s The hottest year everThis fits with the long-term trend.

Analysis70 years of data have shown that extreme heat days are rising faster than the average temperature increase across Aotearoa. Nevertheless, rainfall is decreasing in many places.

Recent heat waves are associated with a current La Niña event. Warming ocean watersThe northeasterly winds and Aotearoa are responsible for warmer air temperatures.

Another contributing factor is Atmospheric blockingAllowing air to heat further by slowing down air movement These processes, together with global warming, will cause More frequent heat wavesIn the coming years.

What is a heatwave and how can it affect you?

While the answer may seem obvious (it’s a hot day), defining a heatwave scientifically is a little more complicated because “hot” is a relative term.

In hotter parts of the world, where temperatures are often above 30℃, a heat wave may be well above 40℃. A heat wave in cooler climates is more likely to cause physiological stress at lower temperatures.

Here in Aotearoa, our climate is milder and the current definition of a hot day is above 25℃. This threshold is where beef and dairy cows can breed. Heat stress.

It is sensibler to define extreme temperatures. Comparative to the mean temperature. This statistical method allows for the identification of heatwave patterns in different areas and months. February and March both had heatwaves. More heatwavesWaikato has been one of the most vulnerable regions in recent decades.

bull kelp clinging to rocks at beach
Marine impacts: The 2017-18 summer heatwave led to local extinctions in bull kelp.
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How do heatwaves impact biodiversity?

Atmospheric and marine heatwaves often coincide in maritime climates such as New Zealand’s. The 2017-18 summer’s marine heatwaves were the most severe in 38 years. Local extinctions in bull kelp (Durvillaea) in Lyttelton Harbour.

This event will have long-term effects on marine ecosystems. Because bull kelps create complex forests that can support a wide range of organisms, it is likely that this event will have a significant impact on the future.

Experiments Testing the thermal tolerance of sea-urchins (Evechinus chloroticusThey were able to tolerate heat stress, but they had limited adaptability as the oceans continue to heat up.

We know less about the effects of atmospheric heat waves upon terrestrial and freshwater organisms. Our Recent reviewSome studies of the average warming in alpine areas were included in literature describing the impacts of climate change on our native biodiversity.




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Warmer winters could allow invasive mammal and bird species to expand their ranges. This may reduce the availability of cool, safe hiding spots for forest birds. Thermal squeeze.

Warmer water may also be beneficial. Change the competitionThere are two types of native fish: invasive and non-native. Warmer temperatures may also be beneficial. Change the flowering timein native plant species, causing overlap invasive plant flowering, potentially decreasing pollination chances and reducing the size the next generation of plants.

More local research is required

Although we didn’t find any literature specifically focusing on heatwaves, we can still look at other countries to see the potential impacts.

For treesExtreme heat can reduce photosynthesis and stress in leaves. It can even cause the death of leaves. tree death.

Different species have different vulnerabilities. Some trees have adaptations that allow them to survive extreme weather. We have very limited data about our native tree species.




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Animals, including birds, reptiles, and insects, are mobile, so they may be able avoid the worst effects from a heatwave. However, we don’t know enough to confirm this.

Long-term, heatwaves can have lasting effects on plants that are affected.

Native forest: Plants that are stressed may be more vulnerable to diseases such as myrtle or kauri death.
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Why are heatwaves so dangerous?

Extreme heat can cause severe physiological stress. Heat isn’t the only problem. Sometimes heatwaves occur at the same moment as droughts. Multiple stressors can be extremely damaging, especially to plants.

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To conserve water, plants use stomata (leaf pores), to close them. However, avoiding high temperatures by reducing water loss through stomata can be difficult because transpiration from the leaf acts as an evaporative cooler to reduce leaf temperature.

Plants that have sufficient soil water are more able to withstand heat death than those that are in drought. Experimental studiesDrought-affected plants may exhibit a tendency to open (rather that close) their stomata as a response to heat. This could increase water stress and increase the likelihood of plant death.




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Stressed plants are more susceptible to pathogens and diseases such as kauri dieback Myrtle Rust. Fire is another risk, as dead and dried plant material can catch fire. more flammableThis increases the severity and incidence of fires.

Extreme weather events are Highly influential in ecology. Extreme climate events can be especially dangerous for small numbers of rare plants and animals. More research is needed to determine their potential effects on a changing climate in Aotearoa.

close up of leaf
Plants can save water when soils are dry by closing their ‘pores’, but this can also reduce their ability to shed heat.
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What about our gardens, though?

To ensure that your garden plants survive the heat, make sure they are well-watered. It is best to water in the evening or late afternoon so that the soil has time to absorb the water. To ensure you are not wasting water, check the water restrictions in your area.

Our researchMany native trees are well-adapted in dry conditions. They may have developed water-saving strategies as a result of low-nutrient soils. These characteristics make them ideal for gardens that are low maintenance and suitable for local conditions.

When planning or changing a garden for the future, it is important to choose plants that are less susceptible to drought.

The current summer conditions are here to stay so be prepared for heatwaves in the long-term.

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