Sine qua non

The view of Lake Mead from the Hoover Dam. The water level is 36 metres below its level at the time of my last visit in 1986.

The view of Lake Mead from the Hoover Dam. The water level is 36 metres below its level at the time of my last visit in 1986. The two towers are structures around the intakes for water extraction and electricity generation.

During my recent holiday in California I received NASA’s Natural Hazards ‘weekly update’. It arrived on my phone while I was in Los Angeles, relaxing by a gurgling water feature.

The following sections have been updated in the past 7 days.

— CROPS AND DROUGHT (1 updated events, 1 new images) —

A serious drought settled over California in early 2014.
 *** Image from Jul 07, 2014 (Posted on Jul 23, 2014 4:32 PM)

Natural Hazards is a service of NASA’s Earth Observatory.

I was shocked to find that I was apparently on holiday in a ‘natural hazard’.

The e-mail highlighted recent research that tried to assess the net long-term reduction in water resources in the Western US, including not only above-ground reservoirs but also underground water. The basin of the Colorado river is apparently down by 65 cubic kilometres in the last 14 years. It may seem unnecessary to say – but a cubic kilometre is a truly phenomenally large amount of water!

These measurements – based on detection of minute changes in the gravitational effect of ground water on satellites (!) – are very difficult. And so it is hard to know exactly how much one should trust their detailed conclusions. But their general conclusion seems pretty sound: California is drawing on its water resources at a faster rate than those resources are being replenished.

This is news to nobody. While in California we saw many adverts and heard radio anouncements urging water conservation. Even amongst the extravagance of Hearst Castle, there were no fountains, the swimming pools were empty, and the toilets were replaced by chemical toilets

Sign on the door of the Hearst Castle Visitor Centre, near San Luis Obsipo, California

Sign on the door of the Hearst Castle Visitor Centre, near San Luis Obsipo, California

But nothing conveys the magnitude of the problem more powerfully than the declining level of the largest reservoir in the US: Lake Mead, trapped behind the Hoover Dam.

Since my previous visit in 1986, the level of water in the 600 square kilometres of Lake Mead has fallen by approximately 36 metres, representing the loss of 21 cubic kilometres of water storage. The lake is now less than 40% full.

Graphing the elevation above sea level (in feet) of the surface of Lake Mead. The 'error bars' shows the annual variation. WHen the level reach 1075 feet, water withdrawals will be automatically scaled back.

The elevation above sea level (in feet) of the surface of Lake Mead versus year. The ‘error bars’ shows the annual variation. When the level reach 1075 feet, water withdrawals will be automatically scaled back. The fall in 1965 resulted from reduced inflows due to the filling of an upstream reservoir – Lake Powell. Click for a larger version.

This level represents the balance between the water drawn from Lake Mead, and the inflows from snow-melt in the Colorado mountains.

Inflows to Lake Mead are typically 10 cubic kilometres annually but annual outflows have been around 11 cubic kilometres.

The low level of Lake Mead in some ways represents a triumph – this is why the Hoover Dam was built: to allow water users to be able to rely on water being available through a drought.

But the prolonged decline results from poorly-drawn water ‘rights’ that allow states to withdraw water at a rate exceeding the long-term average.

When the level reaches 1075 feet – the red line on the graph – then water restrictions will be automatically implemented and presumably the level will stabilise and hopefully recover.

What struck me powerfully on my visit to Las Vegas and the vast metropolis of Los Angeles was that water is the sine qua non of civilisation. And these cities have been built in a natural desert.

Of course all that is required is a reduction in water usage, which will probably equate to an increase in the price of water.

It is hard to see how this situation will evolve – but the first rule of futurology is that the future is likely to be similar to the present day, but different.

And perhaps all that it will take is for the growing of crops less suited to the desert (such as rice!) to move to other parts of the world.

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2 Responses to “Sine qua non”

  1. Bernard Naylor Says:

    Michael: an interesting and challenging post as usual! We have visited two places where the availability of water as an essential for habitation has been acknowledged for centuries and provision has been made. Bermuda was settled by the British in the early 17th century. The island has no rivers or springs and is dependent entirely on rainfall. For hundreds of years, every building is required to be constructed over a cistern (to hold its water supply) and roofed so as to maximise water collection. People are encouraged to shower ‘in the Danish style’. That is, you wet yourself all over, SWITCH OFF THE SHOWER, then soap/wash yourself, and finally run the shower again to wash off the soap. I understand this is also the shower method much used in Denmark where water supply is also a bit problematic.

    In Madeira on the other hand, the Portuguese settlers realised from the early 1500s that water supply was crucial. There, rainwater falls on a high central plateau and oozes out naturally through the sides of the plateau. The Portuguese have built – and, indeed are still building – a system of channels called levadas which brings the rainwater gently down, at a walking pace flow rate, into reservoirs, especially a major one above Funchal, the main settlement. There is also a primitive, but effective system of dams/diverters to route the water most effectively. The levadas were originally built by convict labour; convicts’ lives were cheap! Nowadays, the maintenance and development of the levadas is an ongoing task of the island government.

  2. Care for a Danish-Style Shower? | Protons for Breakfast Blog Says:

    […] couple of weeks ago when I wrote about the continuing Californian drought, my friend Bernard Naylor commented that in many cultures people had adapted to a climate in which […]

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