On the horn of Africa, ten million people are now at risk as the region suffers the worst drought in half a century. In China, the Yangtze—the world’s third largest river – is drying up, parching farmers and threatening 40 percent of the nation’s hydropower capacity. In the U.S. drought now spreads across fourteen states creating conditions that could rival the dust bowl; in Texas, the cows are so thirsty now that when they finally get water, they drink themselves to death.
And yet this apocalyptic dryness comes even as torrential springtime flooding across much of the United States flows into summer; even as half a million people are evacuated as water rises in the same drought-ridden parts of China.
It seems that this year the world is experiencing a crisis of both too little water and too much. And while these crises often occur simultaneously in different regions, they also happen in the same places as short, fierce bursts of rain punctuate long dry spells.
The Climate Connection
Most climate scientists agree that one of the likely effects of climate will be an acceleration of the global water cycle, resulting in faster evaporation and more precipitation overall. Last year, the Proceedings from the National Academy of Sciences published a study which suggested that such changes may already be underway: according to the paper, annual fresh water flowing from rivers into oceans had increased by 18 percent from 1994 to 2006. It’s not hard to see how increases in precipitation could lead to greater flood risk.
At the same time, many studies make the case that much of the world will be dramatically drier in a climate-altered future, including the Mediterranean basin, much of Southwest and Southeast Asia, Latin America, the western two-thirds of the United States among other places.
Both the increase in drought and flood take place in the context of a widespread inter-annual increase in precipitation variability; in this context it’s not surprising that the world would experience both more floods and droughts simultaneously.
Droughts, Floods and Sprawl
Global warming is not the only way that human beings have impacted the global water cycle. Deforestation contributes to both flood and drought; urbanization has an impact as well. As far back as 1968, a study of suburban Northern Virginia found that urban and suburban development “significantly affects flood flows,” and blames a combination of reduced drainage lag-time and increased runoff from impervious surfaces for increasing flood peaks from two to eight times.
Atlanta, Georgia, provides a more recent case study of the paradoxical relationship of urbanization to flood and drought. In recent years, along with much of the Southeastern United States, Atlanta was plagued by severe drought, with 2007 as the driest year in 75 years. But in September of 2009 the city was hit with unprecedented 500-year flooding.
According to the USGS, Atlanta is the number one “most land-consuming metropolitan area” in the United States. The survey blames Atlanta’s development in part for contributing to the severity of the drought, pointing to a study suggesting that compared to 1982, in 1997 the amount of potential groundwater recharge lost to runoff in the region was between 57 and 133 billion gallons—enough to meet the daily household water needs of 1.5 to 3.6 million people per year. “Since the area has continued to see a steady increase in development since the study conducted in 1997, one can only assume that the amount of water not infiltrated today is even more,” the report concludes.
From 1980 to 2000 the population of Atlanta increased by 46 percent, while developed land increased by 81 percent over about the same time period, which also amounted to an increase in the percent of impervious or paved-over landscape of 15 to 35 percent.
Growing Populations at Risk
Amidst all of this, it’s worth keeping in mind that human beings are more likely to notice droughts and floods when they impact us directly. Growing populations, urban sprawl and building on floodplains put more people and assets at risk.
The same is true for drought. The US southwest, for instance — a drought-prone part of the world that many climate scientists believe will only get drier in the future — is the fastest growing part of the country. Since the 1950s, the number of people living in the desert cities of Las Vegas and Phoenix has exploded, rising from a few thousand to metro areas encompassing two and four million respectively. Phoenix was recently hit with a 4,000-foot-high dust storm reminiscent of the 1930s dust bowl, even as wildfires ravaged parts of five southwest states: New Mexico, Arizona, Colorado, California and Texas.
US cities are not alone. The Australian environmentalist Tim Flannery once predicted that water shortages would at some point force people to abandon of Perth, Australia, making it the world’s first “ghost metropolis.” Last February, wildfires destroyed dozens of homes in suburban Perth.
Will we learn anything from this year of deluge and desiccation?
In the end, climate-related water risks of drought and flood are not limited to those who are unfortunate enough to live in the most at-risk regions, because, whether through supply chain disruptions or global political unrest, in a globalized world, what happens to water on the other side of the country or the planet affects us at home.
Read about the Columbia University Global Flood Initiative.