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Harsh Droughts Can Actually Start Over Oceans

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Droughts conjure images of vast expanses of hard, cracked soil and parched plants, but new research suggests that disastrous dry spells can develop over the wettest place of all: the ocean. Low-moisture air masses sometimes form and migrate thousands of kilometers over the sea, similar to the way hurricanes behave. These dry-air regions are less coherent, changing shape as they develop, however, and they move much slower. Some take more than half a year before they hit land, where they can destroy crops and threaten water security. Yet the long travel time means forecasters might be able to predict when this newly recognized type of drought will impact key regions, such as the western U.S.

“Thinking about droughts as a dynamic hazard is a new idea,” says environmental engineer Julio Herrera Estrada, who helped discover the phenomenon. He and his Stanford University postdoctoral advisor Noah Diffenbaugh describe what they have dubbed “landfalling droughts” in a study published this fall in Water Resources Research.

Herrera Estrada and Diffenbaugh made their discovery by retroactively following areas of relatively low atmospheric moisture worldwide, over both land and sea, from meteorological records between 1981 and 2018. “We watched them change shape from month to month and tracked how they moved in space and time,” says Herrera Estrada, who now focuses on sustainability as an applied scientist at Descartes Labs in Santa Fe, N.M. The researchers found that most areas of drought began and ended entirely over either the ocean or land. But one in six of the droughts afflicting continents turned out to have started over the ocean. “It’s not an obvious thing to wrap your head around. It’s a little counterintuitive to think about droughts over the ocean, because it’s wet,” Herrera Estrada says. “But there can still be lower rainfall over the ocean.”

Drought has affected more of the world’s population than tsunamis, earthquakes or any other natural hazard in the past 40 years, killing and displacing people by the millions, according to the United Nations Food and Agriculture Organization. And landfalling droughts are particularly extreme, compared with conventional ones: on average worldwide, they can be one third drier and can grow nearly four times as fast and more than five times larger. The researchers did not investigate why they are more severe, but “one idea is that the atmospheric patterns responsible for landfalling droughts may themselves be different,” Herrera Estrada says. For example, the patterns that create and propel landfalling droughts may be larger than the patterns that drive those that form, and remain, over land.

The hotspots for landfalling droughts seem to include western North America, eastern South America, southwestern Africa and eastern Asia. The researchers are not yet sure why and say the factors that form and influence landfalling droughts may vary in different parts of the world. In western North America, for example, they found that these droughts are linked to areas of high pressure that block rainstorms and thus might initiate dry spells. Herrera Estrada speculates

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Droughts and Human Interference Wiped Out Madagascar’s Gigantic Wildlife 1,500 Years Ago | Smart News

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Thousands of years ago, humans lived alongside behemoths such as giant lemurs, dwarf hippos, giant tortoises and the world’s largest bird, the elephant bird, on the island of Madagascar. These species have long been extinct, leaving scientists to figure out if climate change or human interference are to blame for their disappearance. A new study reports that although droughts created harsher environments for the animals to survive in, “humans were the straw that broke the elephant bird’s back,” reports Elizabeth Pennisi for Science.

Fossils reveal that the giant creatures went extinct around 1,500 years ago, but, until now, the reason why has been unclear. A team led by Hanying Li, a post-doctoral scholar at Xi’an Jiaotong University in China, traveled to Rodrigues—a small, remote island east of Madagascar—to piece together the region’s climatic history, reports David Bressan for Forbes.

The team ventured into the island’s caves to analyze the concentration of oxygen, carbon and other trace elements in the mineral deposits, like the stalactites and stalagmites formed when minerals deposited by water droplets build up. The deposits grow in layers, similarly to tree rings, and reflect fluctuations in temperature and precipitation. Layer by layer, the team reconstructed a climatic timeline for the southwestern Indian Ocean—specifically Madagascar, Rodrigues and another island called Mauritius—dating back 8,000 years. Their findings were published last week in the journal Science Advances.

Analyses of the cave deposits revealed that the region experienced a series of megadroughts that lasted for decades at a time. The most recent dry spell was around 1,500 years ago—around the time when all the megafauna species went extinct. But Madagascar’s wildlife had survived even more severe droughts before, so scientists say that it’s unlikely that the dry climate wiped them out. However, archaeological records showed that human presence increased around that time, and with increased presence comes habitat destruction, overhunting, disease, fire and agriculture. Those stressors, coupled with megadroughts, brought about the end of Madagascar’s megafauna.

“While we cannot say with 100 percent certainty whether human activity, such as overhunting or habitat destruction, was the proverbial straw that broke the camel’s back, our paleoclimate records make a strong case that the megafauna had survived through all the previous episodes of even greater aridity,” Ashish Sinha, a geochemist at California State University, Dominguez Hills and study co-author, says in a press release. “This resilience to past climate swings suggests that an additional stressor contributed to the elimination of the region’s megafauna.”

Kristina Douglass, an anthropologist at Penn State, says that Madagascar is a huge island with a wide range of ecosystems and local climates, plus varying levels of human interference. It’s likely that “the path to extinction is going to look different in different places,” she tells Science.

Within just a couple of centuries of human colonization, native wildlife populations on both Rodrigues and Mauritius were decimated. Rodrigues lost its saddle-backed Rodrigues giant tortoise, for example, and the famous Dodo bird disappeared from Mauritius.

“The story our data tells

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