This weekend, a friend asked me if the rise in the oceans could be drained off into the world’s below-sea-level depressions. Could rising ocean waters be diverted to fill the Dead Sea and Death Valley Depressions, for example? It seems a creative solution. Instead of flooding the Maldives, Piazza San Marco, and south Florida, the expected ocean level rise could fill some of the Earth’s less inhabited wastelands instead.
At this moment, I don’t want to debate the idea of climate change and its impact on sea level. I think the evidence is substantial that Arctic ice and mountain glaciers are disappearing and the melt water is reaching the sea. But this may ultimately be a thousand-year-long melting blip before the return of another ice age. I don’t know. What I’d rather do today is simply try to put some numbers on the innocent question: Would it be practical to relieve coastal flooding by filling land-locked places that are below sea level?
Solving this question is relatively trivial and the answer may surprise you. Using Global Mapper, I loaded a digital elevation overlay, then contoured the outlines of many of the planet’s below-sea-level depressions. There are 49 countries containing land with elevations that are below sea level so there are a number of places to hide future flood waters. Some depressions are small and deep (including Turfan, China and Akdzhakaya, Turkmenistan) while others are broad and shallow. I measured these and the areas of subsea regions such as the Dead Sea and Afar depressions, the gigantic Qattar low elevation desert, Death Valley, Salton Trough, and others. Then I estimated the volume of water these basins could hold.
The Dead Sea coastline, as you undoubtedly know, is the lowest dry land on the planet – it is about 429 metres below sea level. The “sea” is within a 5,000 square kilometre depression, much of which is shallower than 300 metres. Nevertheless, the Dead Sea Depression, flooded with sea water, could hold 1,500 cubic kilometres of water. Filling the sink, however, would eliminate some rather nice olive groves and would submerge important historical sites – including Jericho, a town of 20,000 and perhaps the oldest community on Earth.
Other desert depressions are less populated, so (other than some camel operators) who really cares if they get wet? In particular, there’s the vast north Africa Qattar Depression which covers about 25,000 square kilometres. If we include other low Saharan regions in Tunisia, Libya, and Algeria, we may find as much as 50,000 square kilometres of sand sit below sea level. One may argue that this territory is less attractive than the Dead Sea or Death Valley which we have also slated for drowning, but the enormous Sahara tracts are not deep. Much is barely a single meter below sea level. So, despite being vast in area, the volume of water potentially held is less than a fully inundated Dead Sea.
Continuing around the world, we may be able to siphon 7,500 cubic kilometres of water from the ocean, pumping the sea’s brine into the planet’s various depressions. That is a huge quantity of sea water and should take the pressure off the folks in Miami. But, unfortunately, it turns out to be a trivial drop in the proverbial bucket.
The Earth is a big place. The oceans cover 360 million square kilometres. A meter of sea level rise is a volume 50 times greater than all of the depressions that are below sea level in the world. Climate scientists tell us that the ocean’s waters are presently rising at a rate of about 3 millimetres a year, or 3 centimetres a decade. In just ten years, all of those hypothetical sinks would be full and the waters will still be rising. Because the actual rate of melting is increasing through an amplifying feedback loop, we are told to expect about a meter of sea level increase in the next hundred years or so. It will likely take several centuries for all the world’s ice to melt. By then, the oceans will be 75 metres deeper than they are today.
The bottom line? Flooding Jericho will not save Miami’s Fontainebleau. Nor, if seas rise unabated, will we save Venice, New York, nor the homes of three billion of the planet’s seaside dwellers. Rather than attempting to hide the meltwater, it appears that we need to think of another plan to do something about the impending flood.