Once Every 1,000 Years
Annotated version:
A time-lapse of satellite images showing Cape Town’s largest fresh water reservoir (Theewaterskloof Dam) depleting to historical lows after 3 successive dry years.
Images are generated as a false color combination of Near Infrared, Green, and Coastal/Aerosol (Landsat-8 bands 5, 3, 1) to highlight vegetation (red, orange) and coastal/inland waters (shades of blue).
As of Feb 2, 2018, the reservoir is at 12.2% capacity. The city of Cape Town currently forecasts Day Zero — “the day the taps will be turned off” — to arrive Apr 16 2018 . If and when that day comes, the city plans to provide 200 water distribution stations to allocate 25 liters per person per day. The average American uses over 300 liters of water per day.
Learn more below:
“Cape Town’s Reservoirs Are Getting Terrifyingly Low”
“As things stand, the challenge exceeds anything a major city has had to face anywhere in the world since the Second World War or 9/11,” Helen Zille, the Premier of the Western Cape, wrote in an op-ed late last month. “I personally doubt whether it is possible for a city the size of Cape Town to distribute sufficient water to its residents, using its own resources, once the underground waterpipe network has been shut down.”
The city got to this point because rains have failed the past three years. Last year was Cape Town’s driest year on record, taking the record from 2016. Oh, and 2015 was the fourth-driest year ever recorded at the city’s main weather station at the airport.
“How severe is this drought, really?”
[Piotr Wolski at Climate System Analysis Group]
Some time ago, I’ve heard a story told by an old Kenyan herdsman. The Madala said that every now and then, his village experienced a cattle-killing drought. Every decade, or so, they experienced a goat-killing drought (goats being more sturdy than cows, would die only if conditions were more extreme). And once in a man’s (woman’s of course too) lifetime, they would experience a man-killing drought.
So is Cape’s drought cattle-, goat- or man-killing one? This question can, of course, be rephrased in scientific terms — what is the return interval of the drought we are experiencing? Which basically means: how often, on average, can we expect a drought of a magnitude of the one that we have now, or more severe, to occur?
“Cape Town’s Water is Running Out“
[NASA Earth Observatory Image of the Day]
Piotr Wolski, a hydrologist at the Climate Systems Analysis Group at the University of Cape Town, has analyzed rainfall records dating back to 1923 to get a sense of the severity of the current drought compared to historical norms. His conclusion is that back-to-back years of such weak rainfall (like 2016–17) typically happens about once just every 1,000 years.
Population growth and a lack of new infrastructure has exacerbated the current water shortage. Between 1995 and 2018, the Cape Town’s population swelled by roughly 80 percent. During the same period, dam storage increased by just 15 percent.
The city did recently accelerate development of a plan to increase capacity at Voëlvlei Dam by diverting winter rainfall from the Berg River. The project had been scheduled for completion in 2024, but planners are now targeting 2019. The city is also working to build a series of desalination plants and to drill new groundwater wells that could produce additional water.
License, Sources, and Technical Notes:
- First two animated GIFs licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License
- Landsat-8 bands combination: 5 (near infrared), 3 (green), 1 (coastal/aerosol)
- Source GeoTiff files from Google Cloud Public Datasets:
‘LC08_L1TP_175084_20131218_20170427_01_T1’,
‘LC08_L1TP_175084_20141018_20170418_01_T1’,
‘LC08_L1TP_175084_20150223_20170412_01_T1’,
‘LC08_L1TP_175084_20160109_20170405_01_T1’,
‘LC08_L1TP_175084_20161226_20170315_01_T1’,
‘LC08_L1TP_175084_20171010_20171024_01_T1’,
‘LC08_L1TP_175084_20171127_20171206_01_T1’,
‘LC08_L1TP_175084_20180114_20180120_01_T1’ - Made in Python with Jupyter notebooks, geojson.io, rasterio, ezgif.com
