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作者:百科 来源:知識 浏览: 【大中小】 发布时间:2024-11-21 21:25:59 评论数:
It's 2018. Donald Trump is president of the U.S., Elon Musk will soon send a sports car into space aboard a massive rocket, and Cape Town, South Africa, will run out of water in 79 days.
Triggered by an intense drought, officials in Cape Town are poised to turn off the taps to about 3.2 million people on or around April 12. Given seasonal rainfall patterns, it's doubtful to impossible to avoid this once-unthinkable situation, since the region is in the midst of its typical dry season and unlikely to get much rain before then.
SEE ALSO:These visualizations make disturbing 2017 temperature milestone look like modern artThe drought in Cape Town began in 2015 and has refused to yield. It's brought the community closer and closer to "Day Zero," which is the point when the water in the reservoirs no longer can provide safe drinking water. That date has been pegged as April 12, recently revised from April 21, according to the Western Cape Water Supply District.
The predicament the city finds itself in is ironic, since the municipal government has been at the forefront of the movement for global cities to take a leading role in the fight against climate change. The city has sought to cut its emissions of global warming pollutants, such as carbon dioxide. But now the region finds itself in the grips of a withering drought that may be exacerbated by climate change, forcing city and regional agencies to take draconian actions to curb water use.
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Once water in the reservoirs falls below a certain level, residents won't have running tap water or water to flush their toilets, businesses and schools may be forced to close, and other significant disruptions will take place.
According to meteorologist Bob Henson at Weather Underground, last ditch efforts to avoid Day Zero could include accessing groundwater supplies, which would involve drilling deep wells, and constructing portable desalination plants that convert salt water to fresh water.
The six dams supplying Cape Town with water stood at just 27 percent of capacity as of Jan. 24., according to the Western Cape Water Supply District. A media statement issued by the district said Cape Town residents are still using too much water when compared to the restrictions in place.
Cape Town is located in an area that has a Mediterranean climate, with a wet season lasting from about June through September, when a series of cold fronts and low pressure systems strafe the region with rain and wind. From October to April, during the region's summer months, the weather systems tend to spin up to the south of South Africa, leaving an area of high pressure in control that keeps much of the country dry.
Climate projections show that droughts like this ongoing one are likely to become more common as the Earth warms in response to higher amounts of greenhouse gases in the air. In the case of South Africa, climate models project that areas of tranquil high pressure will become more common, sapping the atmosphere of moisture and lift needed to produce rainfall.
Bare sand and dried tree trunks standing out at Theewaterskloof Dam, near Villiersdorp, South Africa.Credit: Roger bosch/AFP/Getty ImagesClimate models project continued year-to-year variability in rainfall in Cape Town, with a net decrease in precipitation over time.
"Not a permanent drought. Dry years and wet years. And “moderate” years in between. But the chance of dry years increases as we go towards the end of the century," wrote Piotr Wolski, a hydroclimatologist at the University of Cape Town.
"And the chance of wet years decreases as we go towards the end of the century. That’s our New Normal, at least on the rainfall side."
Wolski analyzed rainfall data for the areas near Cape Town's dams and found that the ongoing drought, which began in 2015, has a return period of about 311 years.
This figure shows a trend in rainfall in the WCWSS region over the last 84 years. That trend is towards lower rainfall.Credit: Piotr wolskiHe found that there has been a trend toward declining rainfall in Cape Town during the past 84 years, which is increasing the odds of severe droughts. This is in keeping with other climate data from elsewhere in the world that shows that climate change intensifies hydrological extremes, such as droughts, by raising temperatures and evaporation rates.
"Simply, if that trend was not there, a drought of [the] magnitude experienced in 2017 would be much less likely. Or, to put it in another way, if that trend was not there, then the 2017 drought would likely be much less severe," Wolski wrote on his blog.
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