The Science of Doom

In the last article we looked at trends in extreme rainfall. Now we’ll take a look at what the 6th Assessment Report (AR6), chapter 11, says on floods.

Here’s the plain English version:

The Special Report on Extremes in 2012 and the 5th Assessment Report in 2013 didn’t know whether floods were getting worse globally. There have been lots of studies since but they are still regional and sub-regional so it’s still not possible to measure whether floods are getting worse on a global level.

This isn’t bad news or good news, it’s uncertainty. But if you learnt about climate from the media this may be surprising.

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In #1 – #6 we looked at trends in tropical cyclones from chapter 11 on extreme weather of the IPCC 6th Assessment Report (AR6), with a summary article.

Now we’ll take a look at Extreme Rainfall. It’s needed to understand changes in floods.

There are a number of ways to characterize extreme rainfall – so it’s more complicated than something like annual rainfall which only has one number.

The idea is that even without annual rainfall changing there can be a shift towards more rainfall falling in a given day or a short period – more dry days, more intense rainfall on fewer rainfall days. If you have more extreme rainfall you have more chance of floods.

Warm air holds more moisture, so in a warmer climate we expect more rainfall. The actual physics is more complicated as another factor pushes the other way. A topic for another day. This article is about trends – what do we observe?

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In parts #1 through #6 of this series we’ve followed the six metrics on tropical cyclones (TCs) that are discussed in chapter 11 on Extreme Weather of the IPCC 6th Assessment Report.

The conclusion of this section of chapter 11 on TC trends says:

In summary, there is mounting evidence that a variety of TC characteristics have changed over various time periods.

It is likely that the global proportion of Category 3–5 tropical cyclone instances and the frequency of rapid intensification events have increased globally over the past 40 years. It is very likely that the average location where TCs reach their peak wind intensity has migrated poleward in the western North Pacific Ocean since the 1940s. It is likely that TC translation speed has slowed over the USA since 1900.

Here’s my summary. It’s a little different..

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In #1 we looked at the trends in intensity and frequency of landfalling tropical cyclones (TCs) over 120+ years. In #2 we looked at the same metrics out over the ocean using satellite data, which is available for about the last 40 years. In #3 we looked at “translation speed” or changes in the speed at which the overall TCs are moving. In #4 we looked at trends in rainfall in TCs – missing in action from the IPCC report. And in #5 something called “intensification rates” of TCs.

This is the last trend in TCs that we’ll look at from the 6th Assessment Report.

Here’s the plain English version of the report:

Tropical Cyclones are moving away from the equator towards the poles, at the rate of about 50-60 km (30-40 miles) per decade.

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In #1 we looked at the trends in intensity and frequency of landfalling tropical cycles (TCs) over 120+ years. In #2 we looked at the same metrics out over the ocean using satellite data, which is available for about the last 40 years. And in #3 we looked at “translation speed” or changes in the speed at which the overall TCs are moving.

We’re looking primarily at what the IPCC 6th Assessment Report (AR6) has to say, from section 11.7.1.2 “Observed Trends”.

I was expecting to review what this section said about trends in TC rainfall. The simple climate science idea is that warmer air holds more moisture. As the planet warms we expect more rainfall. This idea will be explained in more detail in future articles on floods.

Here’s the plain English version of trends in TC rainfall from the report:

.

.

It’s not mentioned in the section on Observed Trends. I was surprised.

– I’m moving to Substack. It’s a great publishing platform. See the rest this article (for free) at Science of Doom on Substack.

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