Essay by Eric Worrall
“… But it is not clear how much of this remarkable regional increase in severe rains is due to climate change, or how widespread it is …”
Landmark new research shows how global warming is messing with our rainfall
Published: July 26, 2024 6.20am AEST
Steven Sherwood Professor of Atmospheric Sciences, Climate Change Research Centre, UNSW Sydney
Anna Ukkola ARC DECRA Fellow, UNSW SydneyThe past century of human-induced warming has increased rainfall variability over 75% of the Earth’s land area – particularly over Australia, Europe and eastern North America, new research shows.
The findings, by Chinese researchers and the UK Met Office, were published overnight in the journal Science. They provide the first systematic observational evidence that climate change is making global rainfall patterns more volatile.
Climate models had predicted this variability would worsen under climate change. But these new findings show rainfall variability has already worsened over the past 100 years – especially in Australia.
…
Analysis of daily extreme rainfall totals across Australia in present and future simulations revealed future increases were likely to exceed expectations from many past studies. Rainfall is likely to increase more sharply in the most extreme events, and appears to do this nearly everywhere on the continent.
In 2022, we looked at rainfall hour-by-hour in Sydney using radar data. We found the maximum hourly rainfall increased by 40% in Sydney over the past two decades.
Our findings have major implications for Sydney’s preparedness for flash flooding. More intense downpours are likely to overwhelm stormwater systems designed for past conditions. But it is not clear how much of this remarkable regional increase in severe rains is due to climate change, or how widespread it is.
Increasing variability also means a greater risk of drought. Climate models suggest rainfall variability in many parts of Australia will keep increasing, unless greenhouse gas emissions are rapidly reduced.
A change in only a handful of heavy rainfall days can make or break a drought in Australia. This means even small changes in variability can bring more devastating droughts in the future as dry periods become drier.
…
The rainfall variability study;
Anthropogenic amplification of precipitation variability over the past century
WENXIA ZHANG, TIANJUN ZHOU, AND PEILI WU
SCIENCE
25 Jul 2024
Vol 385, Issue 6707pp. 427-432
Editor’s summary
As climate change continues, warming of the atmosphere allows it to hold more water and thus produce more precipitation. A corollary to more rain is the amplification of precipitation variability, a behavior easier to predict than to observe. Zhang et al. used global records of daily precipitation to show that this expected increase in precipitation variability is in fact detectable in the data over the past century. This trend, which is most prominent over Europe, Australia, and eastern North America, will make adaptation more difficult for societies and ecosystems. —Jesse Smith
Abstract
As the climate warms, the consequent moistening of the atmosphere increases extreme precipitation. Precipitation variability should also increase, producing larger wet-dry swings, but that is yet to be confirmed observationally. Here we show that precipitation variability has already grown globally (over 75% of land area) over the past century, as a result of accumulated anthropogenic warming. The increased variability is seen across daily to intraseasonal timescales, with daily variability increased by 1.2% per 10 years globally, and is particularly prominent over Europe, Australia, and eastern North America. Increased precipitation variability is driven mainly by thermodynamics linked to atmospheric moistening, modulated at decadal timescales by circulation changes. Amplified precipitation variability poses new challenges for weather and climate predictions, as well as for resilience and adaptation by societies and ecosystems.
Read more: https://www.science.org/doi/10.1126/science.adp0212
Another of the referenced studies;
Robust Future Changes in Meteorological Drought in CMIP6 Projections Despite Uncertainty in Precipitation
Anna M. Ukkola, Martin G. De Kauwe, Michael L. Roderick, Gab Abramowitz, Andrew J. Pitman
First published: 10 May 2020Abstract
Quantifying how climate change drives drought is a priority to inform policy and adaptation planning. We show that the latest Coupled Model Intercomparison Project (CMIP6) simulations project coherent regional patterns in meteorological drought for two emissions scenarios to 2100. We find robust projected changes in seasonal drought duration and frequency (robust over >45% of the global land area), despite a lack of agreement across models in projected changes in mean precipitation (24% of the land area). Future drought changes are larger and more consistent in CMIP6 compared to CMIP5. We find regionalized increases and decreases in drought duration and frequency that are driven by changes in both precipitation mean and variability. Conversely, drought intensity increases over most regions but is not simulated well historically by the climate models. The more robust projections of meteorological drought compared to mean precipitation in CMIP6 provides significant new opportunities for water resource planning.
Read more: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020GL087820
The models don’t agree but they think some of their model predictions are reliable.
This seems a very short timeframe to call global warming as the culprit. Not only are there other confounding factors, such as massive land use changes, including vastly expanded irrigation and emission of dust and exhaust particulates, and some major volcanic eruptions such as Hunga Tonga, there is plenty of evidence of huge century scale shifts in rainfall which occurred well before anthropogenic warming became a potential issue.
Perhaps when climate scientists stop making so many wrong predictions we can pay more attention to what their uncomfortably divergent models predict.
Meanwhile local city administrations should be spending more money on drains anyway, even without this prediction of worsening floods. That day in 2023 while I was driving through the Sydney floods I saw a sight I’ll never forget – a council worker in flood water up to his waistline bashing at a large blocked drain under his feet with a huge pry bar, to try to save an entire street of houses from the flood. I don’t see how that kind of risky emergency action would ever be necessary if the city had done a proper job of maintaining the drains BEFORE the floods hit. I sure hope he wasn’t injured that day.
Related
Discussion about this post