In #9 we looked at trends in peak streamflow. As there isn’t a global database of floods this is the best proxy for flood risk from rivers and waterways. The result was a surprising decrease globally – the trend was down in some stations and up in others, but the down outweighed the up. This is good news.
And it’s the opposite of the trend in extreme rainfall, which was bad news.
On the subject of extreme rainfall, AR6 summarises it like this, p. 1560:
In summary, the frequency and intensity of heavy precipitation have likely increased at the global scale over a majority of land regions with good observational coverage
On the subject of peak streamflow, here is the AR6 summary, p. 1568:
In summary, the seasonality of floods has changed in cold regions where snowmelt dominates the flow regime in response to warming (high confidence).
There is low confidence about peak flow trends over past decades on the global scale, but there are regions experiencing increases, including parts of Asia, Southern South America, north-east USA, north-western Europe, and the Amazon, and regions experiencing decreases, including parts of the Mediterranean, Australia, Africa, and south-western USA.
[Emphasis added].
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I think you need to explore further, and be clearer why you think a reduced peak stream flow is “good”. Not all rivers flood regularly and reduced peak flow can simply mean the river is drying. Which is more likely bad news. This is especially true in southwest Australia.
It’s also not necessarily good news for ecosystems, which may have follow on bad affects for Humans. I think framing this as ‘good’ and ‘bad’ – a dichotomy, is not as simple as you think, and I’m not sure it’s useful.
Nathan,
I agree with you. I’ve oversimplified.
A few comments:
1. Brevity is not my strong point, and in this series I’m going for brevity. Over-simplification is the inevitable result.
2. This is from the section of the IPCC report on floods. The section is trying to assess recent trends in flood risk.
A reduction in flood risk can also be an increase in drought risk. Pluses and minuses in many aspects of climate.
I was struck reading one of the references on changes in snow melt, I think it was “Trends in snowmelt-related streamflow timing in the conterminous United States”, R.W. Dudley et al 2017. There was less flooding from snow melt in the northwestern US, which led to greater fire risk.
Reduced flooding in some regions can be a negative – greater risk of droughts, greater forest fire risk due to drier ground.
But that idea isn’t popular when you’ve just had floods in your region, especially if it was your house or your community.
3. Most people, even “very interested in climate” people, aren’t going to read the 95 pages of the report on Extreme Weather (when you strip out the exec summary, the references and the tables at the end). It’s hard to digest.
If there was a good summary of what was actually in the report, instead of just the negatives, it would be wonderful. My work would already be done. But we don’t live in that world.
Anyway, I welcome your comment. I will endeavour to balance brevity and nuance.
It seems that the aim of this series is to question why the IPCC doesn’t emphasize ‘good’ news, and my response to that is: “what is good and bad, ‘depends'” so I don’t see your aim as having any objective basis. You’d really need to look in detail at the specifics
I would suggest that peak flow decreases in almost all of these regions: ‘…parts of the Mediterranean, Australia, Africa, and south-western USA.’
is not good, that it’s a sign that areas that already have low rainfall, and possibly decreasing rainfall, are experiencing less run-off, probably because of soil dryness.
“But that idea isn’t popular when you’ve just had floods in your region, especially if it was your house or your community.”
Well, of course, but reduced peak stream flow in areas like Ethiopia or Somalia won’t be popular either.
If you wanted to really explore this you’d need to look at the specific regions.
The aim of this series is to explain in simple terms what the report says on extreme weather.
I can’t help but notice that the summaries fail to summarize important parts of the report, and so I am going to point it out in some articles – two out of 13 articles in total so far.
If you’re uncomfortable with that, just skip the “Summary” articles.
Here’s a few extracts from the main paper (Do et al 2017) cited by the report:
This is a key paper for this section of the report. It likewise doesn’t mention the nuance that peak stream flow reducing might be bad in some regions. It’s about flood risk.