If another drought arrives before trees and other plants have recovered from the last one, the ecosystem can reach a ‘tipping point’ where the plants’ ability to function normally is permanently affected.
A chronic state of incomplete drought recovery may be the new normal for the remainder of the 21st century and the risk of reaching “tipping points” that result in widespread tree deaths may be greater going forward,
The amount of time it takes for an ecosystem to recover from a drought is an important measure of a drought’s severity. During the 20th century, the total area of land affected by drought increased, and longer recovery times became more common, according to new research published by Nature…
…”If another drought arrives before trees and other plants have recovered from the last one, the ecosystem can reach a ‘tipping point’ where the plants’ ability to function normally is permanently affected,” Fang said.
…The team found that drought impacts increased over the 20th century. Given anticipated 21st century changes in temperature and projected increases in drought frequency and severity due to climate change, their findings suggest that recovery times will be slower in the future…
Christopher R. Schwalm et al. Global patterns of drought recovery. Nature, 2017; 548 (7666): 202 DOI: 10.1038/nature23021
Drought-caused tree deaths are produced by a combination of hydraulic failure [cannot transport water from the roots to the leaves] and carbon starvation [closing pores in response to drought], shows new research. The finding, based on a meta-analysis by 62 scientists from across the world, will improve predictive models of how trees die in response to heat, drought, and other climate stresses...
…As the number of hot droughts increases globally, scientists are looking to make more consistent predictions of what will happen to plants and vegetation in the future.
This matters for models used to predict climate change because plants take up a big portion of the carbon dioxide humans pump in the atmosphere. Therefore, the effect of tree death and die-off, as observed globally in recent decades, could affect the rate at which climate changes.
…Trees respond to the stress of drought by closing those pores that let in carbon dioxide. At that point, they need to rely on their stored sugars and starches to stay alive, and could die from carbon starvation if they run out before the drought is over.
On the other hand, if the tree loses too much water too quickly, an air bubble (embolism) will form and the tree has hydraulic failure, it cannot transport water from the roots to the leaves, which becomes lethal as the whole tree dries out…
Adams et al. A multi-species synthesis of physiological mechanisms in drought-induced tree mortality. Nature Ecology & Evolution, 2017; DOI: 10.1038/s41559-017-0248-x
Study finds human-driven changes in climate and land-use in Amazon’s 3rd “1-in-100 year” drought since 2005
man-made warming is accelerating the movement of water through the ecosystem, which can cause drought even if precipitation does not decrease. Warming also causes changes in the large-scale patterns of air motion (atmospheric circulation) that reduces rainfall in this region
…the Amazon region does encounter periodic droughts. There was one in 2005, another in 2010, both of which were 100-year events, and the most recent one in 2015-2016.
[The authors] quantified the precipitation deficits and water storage on the ground. They also used two different vegetation measures of drought. The results showed that the most recent drought was unprecedented in severity. ……
…the authors found that the relationship between water temperatures and drought worked well for prior droughts (the 2005 and 2010 droughts as well as 1983 and 1998 droughts, also El Niño years) but fell apart in 2015-2016.
…the predicted 2015-2016 drought should not have been nearly as severe or as large as it was. The paper also reports that the 2015-2016 drought clearly exceeded that of the 100-year events in 2005 and 2010. So, in approximately one decade, this zone has had three 100-year events. Quite astonishing…
why was SST unable to explain the 2015-2016 drought, like it had for past events? Part of it has to do with land-use changes. That is, human changes to the land surface such as deforestation. Another part is related to warming from greenhouse gases…land-use changes can affect drought. As farmers deforest, for instance, they convert woodlands and forests into agricultural land. This changes not only the darkness (reflectivity) of the land, but it also impacts the transfer of water to and from the atmosphere (evapotranspiration).
how [does] warming affects droughts… As air temperatures increase, air is able to evaporate water more rapidly and dry out surfaces. At the same time, air can contain more water vapor so that when rain does occur, it is more often in heavy downpours. These two changes underlie what is referred to as an accelerated hydrological cycle. Simply put, man-made warming is accelerating the movement of water through the ecosystem, which can cause drought even if precipitation does not decrease. Warming also causes changes in the large-scale patterns of air motion (atmospheric circulation) that reduces rainfall in this region.
Dr. Wang, who told me:
Since oceanic forcing could not fully explain the severity of the latest drought, one will have to account for the roles of greenhouse gas warming, land use land cover changes, and/or dynamic ecosystem feedback in order to advance the understanding, attribution and prediction of extreme droughts in this region. The frequent recurrence of severe droughts in the recent decade may be a precursor of what the future might have in store for this regional climate and ecosystem.
…droughts in this part of the world create an increased risk for desertification and fire occurrence and hurt the region’s ecosystem, harm trees, and accelerate the release of carbon dioxide…
New study shows that the large-scale difference between a warm Atlantic and relatively cold Pacific ocean temperatures plays a fundamental role in causing droughts, and enhancing wildfire risks in California and the southwest.
the Atlantic/Pacific temperature difference shows pronounced variations on timescales of more than 5 years. Like swings of a very slow pendulum, this implies that there is predictability in the large-scale atmosphere/ocean system, which we expect will have a substantial societal benefit.
A new study shows that difference in water temperature between the Pacific and the Atlantic oceans together with global warming impact the risk of drought and wildfire in southwestern North America.
…”we were able to show that without anthropogenic effects, the droughts in the southwestern United States would have been less severe.”
..The new findings show that a warm Atlantic and a relatively cold Pacific enhance the risk for drought and wildfire in the southwestern US. “According to our study, the Atlantic/Pacific temperature difference shows pronounced variations on timescales of more than 5 years. Like swings of a very slow pendulum, this implies that there is predictability in the large-scale atmosphere/ocean system, which we expect will have a substantial societal benefit,”…
…”we can use our climate computer model to determine whether on average the next year will have drier or wetter soils or more or less wildfires. Our yearly forecasts are far better than chance.”…
Yoshimitsu Chikamoto, Axel Timmermann, Matthew J. Widlansky, Magdalena A. Balmaseda, Lowell Stott. Multi-year predictability of climate, drought, and wildfire in southwestern North America. Scientific Reports, 2017; 7 (1) DOI: 10.1038/s41598-017-06869-7
Fluctuations in sea surface temperature are a factor in causing persistent droughts in North America and around the Mediterranean, new research suggests. A team from the universities of Exeter, Montpellier and Wageningen analysed data from 1957-2002 and found sea surface temperatures in the North Pacific and North Atlantic became increasingly variable, and extremes lasted for longer.
Ocean temperatures are a major driver of conditions on land, and the researchers showed that the changes they observed correlated with increases in land temperature variability, and persistence of extreme temperatures. This in turn was associated with persistent droughts in North America and on land around the Mediterranean….
“Our evidence shows that larger and more persistent variations in sea surface temperature have occurred in the North Atlantic and North Pacific and these contributed to more extreme and persistent temperature anomalies on parts of the world’s land surface,” said Professor Tim Lenton, of the University of Exete
…”For instance, a long heatwave can have greater impacts on human mortality than the sum of individual hot days, and multi-year droughts can have greater agricultural economic impacts than the sum of individual dry years,” Professor Lenton said…
Timothy M. Lenton, Vasilis Dakos, Sebastian Bathiany, Marten Scheffer. Observed trends in the magnitude and persistence of monthly temperature variability. Scientific Reports, 2017; 7 (1) DOI: 10.1038/s41598-017-06382-x
Certain hotspots in the country will experience severe reductions in crop yields by 2050, due to climate change’s impact on irrigation, a new study by climate scientists, economists, and agriculture experts finds. The most adversely affected region, according to the researchers, will be the Southwest. Already a water-stressed part of the country, this region is projected to experience reduced precipitation by midcentury. Less rainfall to the area will mean reduced runoff into water basins that feed irrigated fields.
Production of cotton, the primary irrigated crop in the Southwest and in southern Arizona in particular, will drop to less than 10 percent of the crop yield under optimal irrigation conditions, the study projects. Similarly, maize grown in Utah, now only yielding 40 percent of the optimal expected yield, will decrease to 10 percent with further climate-driven water deficits.
…In the Northwest, water shortages to the Great Basin region will lead to large reductions in irrigated forage, such as hay, grasses, and other crops grown to feed livestock. In contrast, the researchers predict a decrease in water stress for irrigation in the southern Plains, which will lead to greater yields of irrigated sorghum and soybean.
Elodie Blanc, Justin Caron, Charles Fant, Erwan Monier. Is Current Irrigation Sustainable in the United States? An Integrated Assessment of Climate Change Impact on Water Resources and Irrigated Crop Yields. Earth’s Future, 2017; DOI: 10.1002/2016EF000473
Water recycling for agricultural use is about to get a major boost through a massive reuse project in California that marks some first-evers.
“Starting as early as December, [Modesto] will sell its highly treated wastewater to struggling nearby farmers. When it’s up and running, Modesto’s experiment should be California’s largest wastewater-to-agriculture reuse project, and it will mark the first time recycled water flows through a federal canal,” Grist recently reported.
“The project will take tertiary-treated sewage from the cities of Modesto, Turlock and Ceres and route it through new pipelines into the Delta Mendota Canal, owned by the U.S. Bureau of Reclamation. From there, it will be purchased by Del Puerto Water District to irrigate crops on some 200 family farms along the west side of the San Joaquin Valley,” News Deeply explained.
The project, known as the North Valley Regional Recycled Water Program, is the “single largest recycled water conveyance project in the country and the first water project for the U.S. Bureau of Reclamation, the owner and operator of the Delta-Mendota Canal,” the Turlock Journalreported. The effort will bring waste-to-farm techniques to some of the nation’s most productive farmland….
After years of intense, record-setting drought across the U.S., particularly in the Great Plains and California, the country is now experiencing its lowest level of drought in the 17 years since the U.S. Drought Monitor began its weekly updates. Less than 5 percent of the U.S. was in some stage of drought as of May 4, the most recent update, compared to the 65 percent mired in drought in September 2012….
…The epicenters of drought were in the central and southern Plains states from 2011 to 2013 and California from 2012 to this winter. At the peak of its drought, more than half of California was experiencing “exceptional” drought conditions, the highest category. At the end of September 2011, more than 85 percent of Texas was in this category.
Both droughts were fueled by a combination of dry weather and repeated, sizzling heat waves. The exceptional heat that blanketed much of the central and eastern portions of the country in 2012 boosted it to the hottest year on record for the U.S., while California experienced back-to-back record-hot years during its drought.
That heat is probably the clearest link between climate change and droughts, as rising global temperatures fueled by increasing concentrations of greenhouse gases in the atmosphere tilt the odds in favor of record heat and away from record cold….
…Perhaps the clearest regional signals of climate change increasing drought are in the already arid Southwest, where droughts are expected to happen more often, last longer and be more intense than in the past. There is also some suggestion of more consecutive dry days for the Southern Plains, which could make it easier for that region to tip into drought…
Region could lose 30 percent of the snowpack it relies on for irrigation and drinking water—and potentially as much as 60 percent—over the next 30 years
Losses ahead could put farms, energy and drinking water at risk, a new study suggests
By Bob Berwyn, InsideClimate News Apr 27, 2017
The American West has already lost between 10 and 20 percent of its mountain snowpack since the early 1980s, and climate change is partly to blame, new research shows. If greenhouse gas emissions are not curtailed, the region could lose 30 percent of the snowpack it relies on for irrigation and drinking water—and potentially as much as 60 percent—over the next 30 years, the authors write.
The loss can’t be explained by natural climate variations alone, however it is consistent with model simulations that include both natural and human-caused changes, the study says. “These results add to the evidence of a human influence on climate that will have severe impacts on our water supply,” said Benjamin Santer, a Lawrence Livermore National Laboratory climate scientist and a co-author of the paper, published last week in Nature Communications….
The crippling wintertime droughts that struck California from 2013 to 2015, as well as this year’s unusually wet California winter, appear to be associated with the same phenomenon: a distinctive wave pattern that emerges in the upper atmosphere and circles the globe. …Scientists at the National Center for Atmospheric Research (NCAR) found in a recent study that the persistent high-pressure ridge off the west coast of North America that blocked storms from coming onshore during the winters of 2013-14 and 2014-15 was associated with the wave pattern, which they call wavenumber-5. Follow-up work showed that wavenumber-5 emerged again this winter but with its high- and low-pressure features in a different position, allowing drenching storms from the Pacific to make landfall.
…The slow-moving Rossby waves at times become almost stationary. When they do, the result can be persistent weather patterns that often lead to droughts, floods, and heat waves. Wavenumber-5 often has this stationary quality when it emerges during the northern winter, and, as a result, is associated with a greater likelihood of persistent extreme events.
…The new research indicates that the wave pattern may provide an additional source of predictability that sometimes may be more important than the impacts of sea surface temperature changes. First, however, scientists need to better understand why and when the wave pattern emerges.
In the paper published in Journal of the Atmospheric Sciences, Branstator and Teng explored the physics of the wave pattern. Using a simplified computer model of the climate system to identify the essential physical processes, the pair found that wavenumber-5 forms when strong jet streams act as wave guides, tightening the otherwise meandering Rossby wave into the signature configuration of five highs and five lows.
“The jets act to focus the energy,” Branstator said. “When the jets are present, the energy is trapped and cannot escape.” But even when the jets are present, the wavenumber-5 pattern does not always form, indicating that other forces requiring study are also at play.
The scientists also searched specifically for what might have caused the wave pattern linked to the severe California drought to form. In the paper published in the Journal of Climate, the pair found that extremely heavy rainfall from December to February in certain regions of the tropical Pacific could double the probability that the extreme ridge associated with wavenumber-5 will form. The reason may have to do with the tropical rain heating parts of the upper atmosphere in such a way that favors the formation of the wavenumber-5 pattern.