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Everybody knows: climate change is making drought and flooding worse

09 Nov 2022 | Science Notes

From no less an authority than Experts we learn via Twitter that “Experts say climate change is making drought and flooding worse across the globe”. The story goes on: “Climate change is intensifying water-related disasters across the world, according to experts.” The start of COP27 in Egypt is the occasion for experts to come forth and tell us the hard truths that everybody knows. And since everybody knows climate change is making floods and droughts worse around the world, there is no need to look up what other experts said, for instance the IPCC in their most recent report. But let’s anyway.

Chapter 11 of the IPCC Sixth Assessment Report, published in August 2021, had this to say about global trends in extreme precipitation (bold added):

“Overall, there is a lack of systematic analysis of long-term trends in sub-daily extreme precipitation at the global scale. Often, sub-daily precipitation data have only sporadic spatial coverage and are of limited length. Additionally, the available data records are far shorter than needed for a robust quantification of past changes in sub-daily extreme precipitation (C. Li et al., 2019a). Despite these limitations, there are studies in regions of almost all continents that generally indicate intensification of sub-daily extreme precipitation, although there remains low confidence in an overall increase at the global scale. (Section 11.4.2)”

And this on flooding (bold added):

“On a continental scale, a decrease seems to dominate in Africa and Australia, an increase in the Amazon, and trends are spatially variable in other continents. In Europe, flow trends have large spatial differences, but there appears to be a pattern of increase in northwestern Europe and a decrease in southern and eastern Europe in annual peak flow during 1960-2000. In North America, peak flow has increased in the northeast US and decreased in the southwest US. There are important changes in the seasonality of peak flows in regions where snowmelt dominates, such as northern North America and northern Europe, corresponding to strong winter and spring warming....In summary, the seasonality of floods has changed in cold regions where snowmelt dominates the flow regime in response to warming (high confidence). Confidence about peak flow trends over past decades on the global scale is low, but there are regions experiencing increases, including parts of Asia, southern South America, the northeast USA, northwestern Europe, and the Amazon, and regions experiencing decreases, including parts of the Mediterranean, Australia, Africa, and the southwestern USA. (Section 11.5.2)”

Regarding the causes of observed changes (italics in original):

“In summary there is low confidence in the human influence on the changes in high river flows on the global scale. In general, there is low confidence in attributing changes in the probability or magnitude of flood events to human influence because of a limited number of studies, differences in the results of these studies and large modelling uncertainties. (Section 11.5.5)”

Turning to droughts:

“Global studies generally show no significant trends in [Standardized Precipitation Index] time series (Orlowsky and Seneviratne, 2013; Spinoni et al., 2014), and in derived drought frequency and severity data (Spinoni et al., 2019), with very few regional exceptions (p. 1573)

Few AR6 regions show observed increases in meteorological drought (Section 11.9), mostly in Africa and South America... a few others show a decrease (p. 1575)”

And regarding the assignment of blame (italics in original):

“There are only two AR6 regions in which there is at least medium confidence that human-induced climate change has contributed to changes in meteorological droughts (Section 11.9). In South-western South America (SSW), there is medium confidence that human-induced climate change has contributed to an increase in meteorological droughts (Boisier et al., 2016; Garreaud et al., 2020), while in Northern Europe (NEU), there is medium confidence that it has contributed to a decrease in meteorological droughts (Gudmundsson and Seneviratne, 2016) (Section 11.9). In other [global] regions, there is inconclusive evidence in the attribution of long-term trends, but a human contribution to single meteorological events or subregional trends has been identified in some instances… In North America, the human influence on precipitation deficits is complex (Wehner et al., 2017), with low confidence in the attribution of long-term changes in meteorological drought (p. 1577)”

But that’s just the IPCC. What would they know? Everybody knows climate change is making flooding and drought worse around the world. You can read it on Twitter.

One comment on “Everybody knows: climate change is making drought and flooding worse”

  1. I think the belief that there is a trend down in flooding in Australia, may be having somewhat of a reality check at the moment. But of course, thats just weather!! Or perhaps, prognosticating on climate trends perhaps should be a little more circumspect, until we have solid data on a couple of 60 cycles, if not at least one 1000 year cycle.

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