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  • Rights: Crown Copyright 2020
    Published 15 October 2020 Referencing Hub media

    Climate change expert Professor James Renwick points out some of the changes we are starting to see regarding weather events.

    Questions for discussion:

    • What is the relationship between warmth and moisture?
    • How does this relationship affect weather and climate?
    • James says that we are not seeing more storms. Why might people think more storms are happening?



    How extremes are changing is really important because extreme events are what really affect us. It’s what we notice. It’s not these gradual changes in temperature and so on. And we’re seeing more high temperature extremes, more dry extremes. Rainfall is becoming more extreme at both ends of the scale.

    So what’s going on there is – the number one thing – the amount of moisture in the air is related to temperature. That’s it – warmer air has more moisture in it, and evaporation works better when it’s warmer. So moisture is evaporated from the oceans and the land surface faster when it’s warmer, so you get more water vapour in the air. So when you have a way of getting that water back out again – such as a storm – then there’s more moisture to fall out of the sky. So the chances are you’ll get a heavier rainfall event than you would have in the past.

    But we’re not seeing more storms. That’s one thing about climate change that you hear quite often – more storms happening. Well, when you get a storm, there’s more heat, there’s more energy, so the storm itself is probably more powerful. But there’s no indication that there’s more storms in total. But when they happen, they’re likely to be more damaging, and that’s the worry.

    And then at the other end of the scale when it’s sunny, it’s warmer, soils dry out faster, evaporation works faster, so you can get into a dry state more quickly. So the chances of getting a drought when it’s fine, they go up as well.

    So just dealing with those differences in rainfall is going to become harder over time in most parts of New Zealand and in most parts of the world actually.

    Professor James Renwick, Victoria University of Wellington
    Earth slice background diagram for evaporation animation, Vasily Merkushev, 123RF Ltd
    Waiho Bridge washout in 2019, Wayne Costello, Storyful
    Photos of Lauder Atmospheric Research Station; cracked earth in dam; tī kōuka tree in Wairarapa drought, photographed by Dave Allen, courtesy of NIWA
    Auckland water dam in drought, NIWA


    This resource has been produced with the support of the Ministry for the Environment and Stats NZ. (c) Crown Copyright.

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