In #10-#13 we looked at recent trends in droughts.
After covering Tropical Cyclones in #1-#6 it was worth doing a summary in part because AR6’s summary missed some good news from the report itself.
In #7-#9 we looked at extreme rainfall and floods and the summary was important because AR6’s summary missed some good news.
I’ve included the full text from p. 1575 below in the notes.
If you check the table in the notes section of #11 we can see that there were 8 regions identified with a rainfall deficit and 6 regions identified with a rainfall increase. These are also listed in the report section before the summary. However, the summary section only says:
There is medium confidence in increases in precipitation deficits in a few regions of Africa and South America.
Of course, people can read the section before and find out that there were places with a rainfall increase (a decrease in droughts). But anyone limiting themselves to only the “summary” would miss out on this good news.
On soil moisture droughts - agricultural and ecological droughts - they say:
..there is medium confidence that agricultural and ecological droughts have increased in several regions on all continents (WAF, CAF, WSAF, ESAF, WCA, ECA, EAS, SAU, MED, WCE, NES: medium confidence), while there is only medium confidence in decreases in one AR6 region.
So this is a good summary.
They also note that hydrological droughts are found in a few places which is also a good summary.
Overall, because the section contains mostly bad news - more droughts in many places - it’s a decent summary.
I did feel that there was an important aspect of the droughts section missing, as discussed in #13, but that’s not a criticism of the AR6 summary.
Notes
The AR6 summary on trends in droughts from p. 1575:
In summary, there is high confidence that AED [Atmospheric Evaporative Demand] has increased on average on continents, contributing to increased ET [actual evapotranspiration] and resulting water stress during periods with precipitation deficits, in particular during dry seasons.
There is medium confidence in increases in precipitation deficits in a few regions of Africa and South America.
Based on multiple evidence, there is medium confidence that agricultural and ecological droughts have increased in several regions on all continents (WAF, CAF, WSAF, ESAF, WCA, ECA, EAS, SAU, MED, WCE, NES: medium confidence), while there is only medium confidence in decreases in one AR6 region (NAU). More severe hydrological droughts are found in fewer regions (MED: high confidence; WAF, EAS, SAU: medium confidence).
References
Seneviratne et al, 2021: Weather and Climate Extreme Events in a Changing Climate. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change
In much of the Western US (where I grew up), drought is by far the most important threat from climate change. Wars over water rights have been raging since the Los Angeles Aqueduct was built in the 1920s to bring water from the eastern slope of the Sierra Nevada to Los Angeles, drying up Owens Lake and producing toxic dust storms. In addition to precipitation droughts and soil moisture droughts and hydraulic droughts, we likely have "WATER-USE DROUGHTS". Water-use may be the biggest cause of drought, especially if increasing transpiration with temperature is being poorly modeled. Your information (in #13) about the current "greening" of the planet and the "greener" Pliocene Warm Period raised serious doubts in my mind that warmer must be drier. I'd like to know more about the models used to quantify soil moisture droughts and the data that shows increasing water vapor deficits.
Anecdotal stories say that rivers that formerly flowed year-round in Northern China apparently no longer reach the ocean much of the year due to water usage. Lakes Mead and Powell (reservoirs) on the Colorado are at record lows - fundamentally because water has been released from them feed the Colorado River Aquaducts (LA, San Diego and the Imperial Valley) and the Central Arizona Project. Yes, these reservoirs are also falling because inflow from the Upper Colorado Basin has not matches these outflows, but water from the Upper Basin is also used to supply areas outside the Upper Basin (Denver, Colorado Springs , Albuquerque, Salt Lake City, and Cheyenne). Phoenix is the fastest growing city in the US (now fifth largest) and the population in the Colorado Basin has more than doubled since 1985. Does the IPCC distinguish between drought associated with climate change and water-use?