Heat and aridity together make for increasingly brutal global-warming-type droughts
Some brutal droughts are raging around the world. The one in Texas has, naturally, been receiving most of the attention in this country (see Warming-Enhanced Texas Drought Is Once in “500 or 1,000 Years … Basically Off the Charts,” Says State Climatologist). Later in the week I’ll blog about the ones hitting Mexico and South America.
But Britain is clearly also being hit by one for the record books, as the UK Guardian reports:
Underground water supplies are being used to keep rivers flowing in the seasons when they are supposed to be replenished
… The impending crisis – which could have widespread consequences for farmers, food production, tourism, industry and domestic life – has been building for the past 18 months. Reservoirs were already low this time last year. Then came 2011, the driest year in England and Wales for 90 years.
In addition, we are now experiencing the driest winter on record, though this could change over the next few weeks, meteorologists have said. The crucial point is that boreholes and reservoirs are now at “notably low” or “exceptionally low” levels. At the RSPB reserve at Titchwell Marsh in Norfolk, springs have dried up and many of the birds, including populations of bearded tits, marsh harriers and reed warblers, are now struggling to find food. Fresh water plants and animals such as water voles are also suffering. “This is a very worrying situation to have at this time of year,” said Grahame Madge, an RSPB official. “This is an incredibly important wildlife site that we cannot afford to have damaged. We are going to have to look very carefully at how we manage water supplies there in coming years.”
A second article warns, “Half of UK households ‘could face water restrictions by April’.”
A key point is that warm weather droughts are much worse than cold weather droughts. Thanks to manmade global warming, future droughts will be fundamentally different from all previous droughts humanity has experienced because they will be very hot weather droughts, as I have written (see Must-have PPT: The “global-change-type drought” and the future of extreme weather).
The Guardian piece makes a similar point:
Whether these problems trigger a full drought in England this summer depends not just on rainfall but summer temperatures. Britain’s worst years for rainfall included 1921, 1933, and 1964, but these were not the worst years for drought. Summers then were relatively cool, and that made up for the lack of water in boreholes and reservoirs.
It was only when heatwaves began to take place, in years when water levels were only fairly low, that there were significant shortages. This occurred in 1911, 1955, and 1976.
In the case of 1976, the effects were devastating. The temperature reached 27C (80F) every day between 22 June and 16 July, and often climbed well above 32C (90F). Crucially, the previous summer and autumn had been very dry, while the winter of 1975-76 was also exceptionally dry, along with the spring of 1976.
Heath and forest fires broke out across southern England at the peak of the drought in August; 50,000 trees were destroyed at Hurn Forest in Dorset; and an estimated £500m of crops were lost across the country. Food prices rose by 12%. Many rivers ran dry.
There have been numerous studies that make clear warm weather droughts are worse. I discuss one from the University of Arizona here: “U.S. southwest could see a 60-year drought like that of 12th century — only hotter — this century.” The study’s news release explains:
Droughts that are accompanied by warm temperatures have more severe impacts on ecosystems, said Meko, an associate research professor in the UA’s Laboratory of Tree-Ring Research.
That should be obvious, though as I will point out in a forthcoming piece on the Texas drought, if you are in denial about global warming, it will be very hard to plan for what is to come.