Why do some trees die in a drought and others don’t?
Scientists from the University of California, Davis, and colleagues examined those questions in a study published in the journal Ecology Letters.
Using climate data and aerial tree mortality surveys conducted by the U.S. Forest Service during four years (2012-2015) of extreme drought in California, they found that when a drought hits the region, trees growing in areas that are already dry are most susceptible.
The research also showed that the effects of drought on forests can take years to surface, suggesting that such effects may linger even after the drought has ended.
Southern Sierra Nevada trees are most vulnerable The study said that trees in the driest and densest forests are the most at risk of dying in an extreme drought.
‘How much drought a tree can take’ "Our analysis found out how much drought a tree can take," said UC Davis Ph.D. student Derek Young, who co-led the study with Jens Stevens, a UC Davis postdoctoral researcher during the study who is currently at UC Berkeley, and Mason Earles, a postdoctoral researcher at Yale University.
The U.S. Forest Service aerial tree mortality surveys in 2015 estimated 29 million trees in California had died after four years of extreme drought.
Long-term climate and competition explain forest mortality patterns under extreme drought.
ScienceDaily, 19 January 2017.
Retrieved June 16, 2017 from www.sciencedaily.com/releases/2017/01/170119143406.htm University of California – Davis.

Summer rainfall in vulnerable African region can be predicted.
Summer rainfall in one of the world’s most drought-prone regions can now be predicted months or years in advance, climate scientists at the Met Office and the University of Exeter say.
The Sahel region of Africa — a strip across the southern edge of the Sahara from the Atlantic Ocean to the Red Sea — is a semi-arid landscape between the desert to the north and the savannah to the south.
The new research used the Met Office Hadley Centre’s Decadal Prediction System and found that the model was good at predicting summer Sahel rainfall over the forthcoming five years.
Forecasting years ahead relies on sea surface temperature in the North Atlantic, whereas the El Niño Southern Oscillation is important for a shorter-term forecast before each summer.
"Our study suggests that skilful predictions of summer rainfall in the Sahel are now possible months or even years ahead," said Dr Katy Sheen, formerly of the Met Office but now of the University of Exeter’s Penryn Campus in Cornwall.
"With a population reliant on agriculture, the Sahel is particularly vulnerable to major droughts, such as those of the 1970s and 1980s.
"Improved understanding and predictions of summer rainfall in the Sahel has the potential to help decision makers better anticipate future cycles of summer droughts and floods, helping local communities become increasingly resilient to the region’s notoriously variable and changing climate."
"Our study improves our understanding of the driving mechanisms of summer rainfall variability and shows they are predictable," Dr Sheen added.
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Danish Funding Supports Vulnerable People In Horn Of Africa Drought And South Sudan.
NAIROBI – The United Nations World Food Programme (WFP) welcomes a US$10.7 million (75 million Danish Krone) contribution from the Government of Denmark to help roll back famine in South Sudan and to assist hungry people in Horn of Africa countries hit by drought.
“If the international community does not act now, the drought in East Africa and the Horn could very easily end up being one of those silent disasters that cost thousands of lives,” said Danish Minister for Development Cooperation Ulla Tørnæs.
The contribution will assist people in South Sudan and support the drought response in Somalia, Ethiopia and Kenya.
In Ethiopia, the contribution will support supplementary feeding for children under the age of five and pregnant and nursing women to combat malnutrition.
In northwestern Kenya, Danish funding will help WFP respond to high malnutrition rates among the most vulnerable women and children under the age of five because of drought.
In 2016, Denmark was the 13th largest government donor to WFP and WFP’s fourth largest donor of flexible funds that allow WFP to respond fast and effectively to disasters, providing life-saving food assistance to millions of people, and to reach those who are left furthest behind.
Follow us on Twitter @wfp_africa @wfp_media For more information please contact (email address: firstname.lastname@wfp.org): Anne Poulsen, WFP/Copenhagen, Tel.
+45 4533 5351, Mob.
+45 4050 3993 Challiss McDonough, WFP/Nairobi, Tel.

Most New Mexicans know climate change is happening and understand it is human-caused. According to recently-released data, New Mexicans are also more likely than people in about half the country to talk not just about the weather, but climate. This week, The New York Times published six maps showing how adult Americans think about climate change and regulations on carbon emissions. The maps were based on data from researchers at Yale University. According to their nationwide survey, 70 percent of Americans think global warming is happening. More than half understand it is human-caused and 71 percent say they trust climate scientists. In their 2016 survey, the Yale researchers drilled down to the local level, allowing a glimpse into how both urban and rural New Mexicans think about climate change and carbon regulations. While more than half of New Mexicans say global warming is happening, and more than 44 percent know that it’s human-caused, opinions vary widely between counties. In San Juan County, only 58 percent say global warming is happening, whereas in Taos County, that number hits 79 percent. Again, in San Juan County, only 44 percent say it’s human-caused, while 63 percent say the same in Rio Arriba and San Miguel counties. When it comes to lightly-populated counties, it’s important to keep in mind the small sample sizes, said John Fleck, director of the University of New Mexico Water Resources Program. But, he said, it’s striking to see how many people across the country understand global warming is a problem. “It runs counter to this narrative that there’s a red-blue divide on this,” he said. “There is a little bit, I guess, but people in general think global warming is a problem and we ought to do something about it.” Fleck also noted that New Mexicans and other southwesterners are more concerned about climate change than people in many other parts of the country. “You’ve got to think that it has something to do with the tenuousness of our water supply in the rural parts of the arid West,” he said. He was also surprised that even in many conservative, coal-rich areas of the country, including Wyoming and West Virginia, people support restrictions on coal and carbon dioxide. Nationally, 75 percent of adults support regulating carbon dioxide as a pollutant. That number is slightly lower here in New Mexico, at 74 percent statewide — ranging from 64 percent in San Juan County to 80 percent in Santa Fe County. Among polled Americans, 69 percent favor strict carbon emissions on existing coal-fired power plants. In San Juan County, where power plants provide jobs, only 45 percent support those limits….

It’s a major natural disaster that slowly grows in one place and then moves across a region, gaining intensity and size.
As it spreads, it destroys land, ruins agriculture and tears apart communities, and it can kill people.
Researchers are just beginning to view droughts as this type of dynamic force, and some hope that soon they will be monitored similarly to hurricanes — with scientists able to predict their development, helping to protect those living in their path.
Ten percent of droughts travel between 1,400 to 3,100 kilometers from where they begin, according to a recent study.
The study, which analyzed 1,420 droughts between 1979 and 2009, identified "hot spots" around the world and common directions in which droughts move.
Some droughts in the southwest United States, for example, tend to move from south to north.
In Central Africa, droughts tend to go southeastern toward the coast.
"It can start somewhere, move throughout the continent, and obviously cause harm throughout its way," Julio Herrera-Estrada, a doctoral candidate at Princeton University and leader of the study, said Thursday.
They can cause a loss of agriculture, wildlife, wetlands and human life, according to the National Drought Mitigation Center in Lincoln, Nebraska.
Very costly They are also one of the most expensive natural disasters that people face today, according to Herrera-Estrada, who collaborated on the study with the International Institute for Applied Systems Analysis in Vienna.