June 02, 2015

Megadroughts vs. the Water Revolution

Cayman Somerville, Innovation Fellow

Unique regional climates create the niche conditions for certain species’ habitats. For example, the greater roadrunner is exclusive to the southwestern United States, where it lays its eggs among bushes or cacti and preys upon desert insects, spiders and serpents. Its habitat is just one example of climates under threat from the increasing prevalence of “megadroughts."

The regional impacts of global warming are expected to be disproportionate, varying from one geographic location to another, depending on their particular temperatures and precipitation levels. Megadroughts -- droughts that last for more than three decades -- will occur only in certain regions.

This past February, NASA published a study depicting the disturbing future for the Southwest and Central Plains regions of the U.S. Using climate models that incorporate soil moisture data to estimate 21st century drought risk, NASA scientists determined that these regions should expect drier and longer droughts than any conditions seen in the last 1,000 years.

The new analysis builds on several recent studies that forecast these regions will experience “extensive droughts in the second half of this century.” However, NASA’s report found that drought conditions in both regions would not only last for at least 35 years, but would also be more severe than all previous predictions -- worse than the megadroughts of the 12th and 13th centuries, which are considered to be the “hottest, most arid extended droughts.”

The researchers found that the advancing of “human-produced” greenhouse gas emissions accelerates the risk of severe droughts in these two regions. The study, published in Science Advances, is based on tree rings, which shed light on past droughts and climate models and can predict future droughts. Soil moisture data taken 30 centimeters below the top layer of soil was standardized to the Palmer Drought Severity Index and deviated from the 20th century average. Using this index, climate scientists analyzed the soil moisture data sets from 17 climate models.

These were used to create two emissions scenarios through the year 2100: a diminished emissions scenario or a high emission scenario. Currently, the likelihood of a megadrought persisting in the Southwest and Central Plains is 12 percent.  If greenhouse gas emissions are mitigated by 2050, the researchers claim a megadrought has a 60-percent likelihood of occurring. Alternatively, if emissions continue along their current trajectory of increase, the likelihood of a decades-long megadrought in these regions reaches 80 percent.

While California and southwestern states cope with an extreme drought, Israel has recently seen a water revolution, becoming the global leader in “recycling and reusing wastewater for agriculture.” This is thanks to a national effort to recycle water and desalinate Mediterranean seawater, resulting in an end to the chronic shortages and over-exploitation of their water resources.  Israel treats more 86 percent of domestic wastewater to be recycled, according to the government's Water Authority, while the U.S. treats only one percent.

The United Nations Intergovernmental Panel on Climate Change (IPCC) released a Fifth Assessment Report, which reported low expectation that soil moisture, one of the main indexes of drought, would improve. Nations should address these environmental challenges early on by investing in new technology and sharing best practices among each other. As scientific understanding of rise in Earth’s average temperature is advanced, an increased urgency to mitigate water challenges and greenhouses gases becomes palpable.