Ecology, Climate Change and Related News

Conservation Science for a Healthy Planet

Category Archive: Drought

  1. NASA satellites reveal major shifts in global freshwater; Groundwater depletion in Central Valley due to drought and agriculture

    Leave a Comment
    • Researchers see a distinctive pattern of the wet land areas of the world getting wetter — those are the high latitudes and the tropics — and the dry areas in between getting dryer. Embedded within the dry areas we see multiple hotspots resulting from groundwater depletion.
    • Significant groundwater depletion observed in California’s Central Valley from 2007 to 2015, is likely due to both decreased groundwater replenishment from rain and snowfall combined with increased pumping for agriculture.

    May 16, 2018  Read full NASA article here

    See related Guardian UK article here: Water shortages to be key environmental challenge of the century, Nasa warns

    In a first-of-its-kind study, scientists have combined an array of NASA satellite observations of Earth with data on human activities to map locations where freshwater is changing around the globe and why.

    The study, published today in the journal Nature, finds that Earth’s wet land areas are getting wetter and dry areas are getting drier due to a variety of factors, including human water management, climate change and natural cycles.

    ….”What we are witnessing is major hydrologic change,” said co-author Jay Famiglietti of NASA’s Jet Propulsion Laboratory in Pasadena, California, which also managed the GRACE mission for NASA’s Science Mission Directorate in Washington. “We see a distinctive pattern of the wet land areas of the world getting wetter — those are the high latitudes and the tropics — and the dry areas in between getting dryer. Embedded within the dry areas we see multiple hotspots resulting from groundwater depletion.”

    For instance, although pumping groundwater for agricultural uses is a significant contributor to freshwater depletion throughout the world, groundwater levels are also sensitive to cycles of persistent drought or rainy conditions. Famiglietti noted that such a combination was likely the cause of the significant groundwater depletion observed in California’s Central Valley from 2007 to 2015, when decreased groundwater replenishment from rain and snowfall combined with increased pumping for agriculture.

    Southwestern California lost 4 gigatons of freshwater per year during the period. A gigaton of water would fill 400,000 Olympic swimming pools. A majority of California’s freshwater comes in the form of rainfall and snow that collect in the Sierra Nevada snowpack and then is managed as it melts into surface waters through a series of reservoirs. When natural cycles led to less precipitation and caused diminished snowpack and surface waters, people relied on groundwater more heavily….

    M. Rodell et al. Emerging trends in global freshwater availability. Nature (2018) doi:10.1038/s41586-018-0123-1

  2. Billions of gallons of water saved by thinning forests

    Leave a Comment
    • Forest thinning could increase water flow from Sierra Nevada watersheds by as much as 10 percent.
    • The U.S. Forest Service says that 6 to 8 of the 21-million acres it manages in California need immediate restoration. Another 58 million acres nationally also require restoration. For California alone, restoration costs are estimated at $5 to $10 billion. But, according to the study authors, the restoration might help pay for itself.

    Posted: 24 Apr 2018 01:02 PM PDT Read full ScienceDaily article

    There are too many trees in Sierra Nevada forests, say scientists. That may come as a surprise to those who see dense, verdant forests as signs of a healthy environment. After all, green is good, right? Not necessarily. When it comes to the number of trees in California forests, bigger isn’t always better….

    That’s in part because trees use lots of water to carry out basic biological tasks. In addition, they act as forest steam stacks, raking up water stored in the ground and expelling it as vapor into the atmosphere, where it’s accessible to humans and forest ecosystems only when it falls back to Earth as rain and snow.

    That process — by which plants emit water through tiny pores in their leaves — is known as evapotranspiration. And according to researchers, excessive evapotranspiration may harm a fragile California water system, especially during prolonged, warm droughts.

    New research published this week in the journal Ecohydrology shows that water loss from evapotranspiration has decreased significantly over the past three decades. That’s due in large part to wildfire-driven forest thinning — a finding with important implications for forest and water management.

    A century of forest management had kept wildfires to a minimum. But without fire, Sierra forests grew very dense. In recent decades, new policies have allowed nature to take its course, with wildfires helping to thin out overgrown forests.

  3. Sierra snow pack at 27% of normal

    Leave a Comment
    • Measurements from 103 stations scattered throughout the Sierra. indicate the snow water equivalent (SWE) of
      • the northern Sierra snowpack is 4.6 inches, 27 percent of the multi-decade average for today’s date central and southern Sierra readings are­­ 5.8 inches (­­30 percent of average) and
      • 3.8 inches (25 percent of average) respectively.
      • Statewide, the snowpack’s SWE is 4.9 inches, or 27 percent of the Feb. 1 average

    Feb 1 2018 Department of Water Resources  read full release at Maven’s Notebook

    Despite moderate January precipitation in the Sierra Nevada after an historically dry December, today’s Department of Water Resources (DWR) manual snow survey east of Sacramento found little snowpack there, two months into what is typically California’s wettest three months.

    Measurements at Phillips Station revealed a snow water equivalent (SWE) of 2.6 inches, 14 percent of the early-February average at Phillips as measured there since 1964. SWE is the depth of water that theoretically would result if the entire snowpack melted instantaneously.

    “California experiences the most variable weather in the nation,” said DWR Director Karla Nemeth. “It’s vital that water conservation efforts remain consistent regardless of the year’s precipitation.”

    More telling than a survey at a single location like Phillips are DWR’s electronic readings today from 103 stations scattered throughout the Sierra. Measurements indicate the SWE of the northern Sierra snowpack is 4.6 inches, 27 percent of the multi-decade average for today’s date. The central and southern Sierra readings are­­ 5.8 inches (­­30 percent of average) and 3.8 inches (25 percent of average) respectively. Statewide, the snowpack’s SWE is 4.9 inches, or 27 percent of the Feb. 1 average.

    “The snow survey today shows water content far below average for this time of year,” said Frank Gehrke, chief of the California Cooperative Snow Surveys Program who conducted today’s survey at Phillips. “Today’s measurements indicate an anemic snowpack to date, but there is still the possibility of a wet February and March.”,,,

  4. Dangerously Low on Water, Cape Town Now Faces ‘Day Zero’; A Warning for California and the American West?

    Leave a Comment

    The Theewaterskloof Dam, the city’s largest, is just 13% full. (AP Photo)

    • After a three-year drought, Cape Town is now at serious risk of becoming one of the few major cities in the world to lose piped water to homes and most businesses.
    • As far back as 2007, South Africa’s Department of Water Affairs warned that the city needed to consider increasing its supply with groundwater, desalination and other sources, citing the potential impact of climate change….
    • New water supplies have been part of the city’s plans but “it was not envisaged that it would be required so soon.”
    • Cape Town’s problems embody one of the big dangers of climate change: the growing risk of powerful, recurrent droughts

    CAPE TOWN — It sounds like a Hollywood blockbuster. “Day Zero” is coming to Cape Town this April. Everyone, be warned.

    The government cautions that the Day Zero threat will surpass anything a major city has faced since World War II or the Sept. 11 attacks. Talks are underway with South Africa’s police because “normal policing will be entirely inadequate.” Residents, their nerves increasingly frayed, speak in whispers of impending chaos.

    The reason for the alarm is simple: The city’s water supply is dangerously close to running dry.

    If water levels keep falling, Cape Town will declare Day Zero in less than three months. Taps in homes and businesses will be turned off until the rains come. The city’s four million residents will have to line up for water rations at 200 collection points. The city is bracing for the impact on public health and social order.

    “When Day Zero comes, they’ll have to call in the army,” said Phaldie Ranqueste, who was filling his white S.U.V. with big containers of water at a natural spring where people waited in a long, anxious line.

    It wasn’t supposed to turn out this way for Cape Town. This city is known for its strong environmental policies, including its careful management of water in an increasingly dry corner of the world….

    But after a three-year drought, considered the worst in over a century, South African officials say Cape Town is now at serious risk of becoming one of the few major cities in the world to lose piped water to homes and most businesses.

    Hospitals, schools and other vital institutions will still get water, officials say, but the scale of the shut-off will be severe.

    Cape Town’s problems embody one of the big dangers of climate change: the growing risk of powerful, recurrent droughts. In Africa, a continent particularly vulnerable to the effects of climate change, those problems serve as a particularly potent warning to other governments, which typically don’t have this city’s resources and have done little to adapt.

    the-south-african-weather-service-says-climate-change-is-making-its-historical-models-useless- theeshop dam AP PhotoThe Theewaterskloof Dam, the city’s largest, is just 13% full. (AP Photo)

    For now, political leaders here talk of coming together to “defeat Day Zero.” As water levels in the dams supplying the city continue to drop, the city is scrambling to finish desalination plants and increase groundwater production. Starting in February, residents will face harsher fines if they exceed their new daily limit, which will go down to 50 liters (13.2 gallons) a day per person from 87 liters now…

    …As far back as 2007, South Africa’s Department of Water Affairs warned that the city needed to consider increasing its supply with groundwater, desalination and other sources, citing the potential impact of climate change. Mike Muller, who served as the department’s director between 1997 and 2005, said that the city’s water conservation strategy, without finding new sources, has been “a major contributor to Cape Town’s troubles.”

    “Nature isn’t particularly willing to compromise,” he added. “There will be severe droughts. And if you haven’t prepared for it, you’ll get hammered.” Ian Neilson, the deputy mayor, said that new water supplies have been part of the city’s plans but “it was not envisaged that it would be required so soon.”…

    ….So far, only 55 percent of Cape Town residents have met the target of 87 liters per day. Helen Zille, the premier of Western Cape Province, which includes Cape Town, wrote in The Daily Maverick last week that she considers a shut-off inevitable. The question now, she said, is, “When Day Zero arrives, how do we make water accessible and prevent anarchy?”

    Cutting back is a difficult message to convey in one of the world’s most unequal societies, where access to water reflects Cape Town’s deep divisions. In squatter camps, people share communal taps and carry water in buckets to their shacks. In other parts of the city, millionaires live in mansions with glistening pools….

  5. Discrepancies between satellite and global model estimates of land water storage– Models may underestimate large water storage changes

    Leave a Comment
    • Overall, the model results calculated a decline in global water storage during the study period, while GRACE data indicate it was on the rise. However, the study notes that while the climate increased water storage globally, humans caused significant declines in certain regions.
    • But ensuring water availability for human consumption and agriculture is in many cases a regional to local issue, and we should put increased emphasis on analyses at this scale by, for example, integrating local data.

    Posted: 22 Jan 2018 01:47 PM PST

    Researchers have found that calculations of water storage in many river basins from commonly used global computer models differ markedly from independent storage estimates from GRACE satellites.

    ….”People are depending more and more on global models to determine projections of the impacts of human water use and climate on water resources,” said lead author Bridget Scanlon, a senior research scientist at the university’s Bureau of Economic Geology. “We are now able to evaluate water storage changes from models with GRACE data, which suggests that the models may underestimate large water storage changes, both large declining and rising storage trends.”

    ….Overall, the model results calculated a decline in global water storage during the study period, while GRACE data indicate it was on the rise. However, the study notes that while the climate increased water storage globally, humans caused significant declines in certain regions. The study area covered about 63 percent of global land area and excluded Greenland and Antarctica because most of the water in those areas is trapped in glaciers or ice sheets….

    …The study also notes that scientists should work on improving regional assessments. “GRACE is great because it highlights the global picture of what’s happening with global water storage, and at a coarse grid-scale it’s really nice to see what’s happening,” Scanlon said. “But ensuring water availability for human consumption and agriculture is in many cases a regional to local issue, and we should put increased emphasis on analyses at this scale by, for example, integrating local data. The specific situation could be much better investigated than with global-scale studies only.”

    Bridget R. Scanlon, Zizhan Zhang, Himanshu Save, Alexander Y. Sun, Hannes Müller Schmied, Ludovicus P. H. van Beek, David N. Wiese, Yoshihide Wada, Di Long, Robert C. Reedy, Laurent Longuevergne, Petra Döll, Marc F. P. Bierkens. Global models underestimate large decadal declining and rising water storage trends relative to GRACE satellite data. Proceedings of the National Academy of Sciences, 2018; 201704665 DOI: 10.1073/pnas.1704665115

  6. Strikingly dry conditions persist; Thomas Fire now largest California wildfire

    Leave a Comment

    by Daniel Swain December 24, 2017 read full CA Weather Blog post here

    Bone dry in Southern California, and below average precip throughout CA

    All of California is now experiencing well-below-average precipitation for the season to date. Southern California has seen almost no precipitation at all…

    Why has California been so dry? (Regular blog visitors already know where I’m going with this.) Well, a remarkably persistent zone of atmospheric pressure has been present more often than not across the region for the past few months. ….More recently, the bigger & stronger West Coast ridge has pushed the Pacific storm track even further north. Remarkably, this powerful ridge has forced several very moist atmospheric river storms over the mid-Pacific to make a hard “left turn” over the open ocean–veering directly northward and bringing almost inconceivably heavy snowfall to the coastal mountains of southern Alaska.

    Thomas Fire becomes largest wildfire in modern California history–in December

    The Thomas Fire has become the largest wildfire in modern California history–in December. (Via NASA)

    ….While December wildfires are not unheard of in this part of the world, the extent and severity of the December 2017 fires in SoCal really is unprecedented in California history. The Thomas Fire–which has now burned nearly 275,000 acres and over a thousand structures in Ventura and Santa Barbara counties–yesterday became the single largest wildfire in modern California history. That this dubious milestone was reached in December, which is typically the midst of the California rainy season, is truly extraordinary. Indeed, recent months have brought not only near-record low precipitation, but also record-high temperatures across a wide swath of SoCal….

    …..While long-term humidity records are hard to come by in most spots, all signs suggest that these were at or near record-low humidity values for many of these recording stations (and certainly for the time of year).

    Is this (another) return of the Ridiculously Resilient Ridge?

    Persistent high pressure ridging over the American West has kept conditions unusually warm and dry so far this autumn and early winter, especially across Southern California and Arizona. (NOAA via ESRL)……we’re not in Triple R [ridiculously resilient ridge] territory quite yet, but we’re getting close. We have certainly witnessed the return of resilient ridging near California, but I don’t think we’ve yet reached the “ridiculous” level of multi-month persistence that occurred during the height of the recent California drought. Should present conditions persist through January, and if seasonal precipitation has not started to recover from its early deficit by that time, I may have to revise that answer.

     

    …The not-so-good news: parts of Southern California that depend exclusively on local water supplies (such as much of Santa Barbara and Ventura counties) never really recovered from the last drought, and these regions remain quite susceptible to the impacts of drought re-intensification. And even further north, forested regions remain quite stressed as a result from the previous multi-year drought, and tree mortality in the Sierra Nevada remains far above historically observed levels.

    Unfortunately, 2+ weeks of unusually dry conditions still probable….The “Warm West/Cool East” pattern discussed in the previous post is still quite prominent over North America. The present West Coast dryness is largely consistent with seasonal model predictions for this winter, and those same models presently suggest that the present pattern is likely to persist for much of the California rainy season.All of this is to say: it’s still too early to say whether we’re headed into a new drought, though there are some compelling signs that we may be (especially in Southern California). And even in a dry year, California can still experience big storms and very wet months. But at this point, it probably makes sense to start thinking about the possibility of yet another big swing in California–from drought, to flood, and then (perhaps) back again.

  7. California has only slim chance of normal rainfall this winter

    Leave a Comment
    • Dettinger of USGS said most of Northern California has either a 33 percent or 34 percent chance of having a normal water year. The chances drop to as low as 14 percent in much of the southern half of the state, where rainfall has been even scarcer so far this season. The water year runs from Oct. 1 to Sept. 30.

    By Dale Kasler Dec 15 2017 Read full SacBee article here

    ….Even if the season had been rainy so far, Dettinger said California would struggle to reach normal precipitation for the season. That’s because most California winters are on the dry side. The wet winters, while relatively rare, are so rainy that they generate the lion’s share of the state’s water supply.

    Dettinger’s findings, reported on a blog run by UC San Diego’s Center for Western Weather and Water Extremes, come amid fresh signs of a difficult water year.

    ….State officials and most forecasters have said it’s still too soon to predict how this winter will turn out, although they’ve acknowledged they’re increasingly concerned about the recent dry spell….

  8. Odds of megadroughts- warming world can produce 30+ year periods of severe drought in western US

    Leave a Comment

    December 14, 2017 Cornell University  read full ScienceDaily article here

    To help untangle fact from speculation, scientists have developed a ‘robust null hypothesis’ to assess the odds of a megadrought — one that lasts more than 30 years — occurring in the western and southwestern United States…

    ….Using tree ring and other physical evidence, researchers determined that the American Southwest saw five megadroughts from 800 to 1300 A.D., a period almost as warm as it is today, though Ault explained that the causes were different, such as solar activity. Today, Ault and his colleagues want to know if an actively warming world can stimulate a megadrought.

    ….”It’s surprising that even with this simple statistical model, we can get megadroughts that are as prolonged, as severe and as widespread as the worst droughts of the last 1,200 years in the west.”…

    Toby R. Ault, Scott St. George, Jason E. Smerdon, Sloan Coats, Justin S. Mankin, Carlos M. Carrillo, Benjamin I. Cook, Samantha Stevenson. A Robust Null Hypothesis for the Potential Causes of Megadrought in Western North America. Journal of Climate, 2018; 31 (1): 3 DOI: 10.1175/JCLI-D-17-0154.1

  9. Climate change and habitat conversion combine to homogenize nature- report on Costa Rican bird studies

    Leave a Comment
    • Land use change and drought favor the same species and threaten the same species so we may be losing biodiversity faster than we previously thought when we were studying these separately
    • Key strategies include protecting areas of wetter forests that expected to stay wet in the future; targetting conservation on wet-forest species that are particularly sensitive to habitat conversion and climate change; and incentivizing  landowners in wet regions to create or maintain patches of forests near or within their farms to better balance food production and biodiversity.

    August 18, 2017 University of California – Davis  Read full ScienceDaily article here

    Climate change and habitat conversion to agriculture are working together to homogenize nature, indicates a study in the journal Global Change Biology led by the University of California, Davis.

    In other words, the more things change, the more they are the same.

    While the individual impacts of climate change and habitat conversion on wildlife are well-recognized, little is known about how species respond to both stressors at once.

    In northwest Costa Rica, the study’s authors surveyed birds and plants at 120 sites that included rainforests, dry forests and farmland to determine how habitat conversion and climate-change-induced droughts affect tropical wildlife. They found that different bird species thrive in drier versus wetter areas of forests. In farmlands however, birds associated with dry sites were found everywhere, even in the wettest sites.


    Green-headed tanager (Tangara seledon). Credit: © Wilfred / Fotolia
    Across Central and South America, we are seeing large areas being converted from native forest to agriculture, and droughts are becoming more frequent,” said lead author Daniel Karp, an assistant professor in the UC Davis Department of Wildlife, Fish and Conservation Biology. “Both of these global pressures are favoring the same species and threatening the same species This means we may be losing biodiversity faster than we previously thought when we were studying climate change and habitat conversion individually.”
    most vulnerable birds at the study sites were those in the wet forests, which include tropical birds like tanagers, manakins, and woodcreepers. He noted that birds in the agricultural sites — such as blackbirds, doves, and sparrows — were more similar to those found in the dry forest, where there is less of a tree canopy and more grass cover….
    Daniel S. Karp, Luke O. Frishkoff, Alejandra Echeverri, Jim Zook, Pedro Juárez, Kai M. A. Chan. Agriculture erases climate-driven β-diversity in Neotropical bird communities. Global Change Biology, 2017; DOI: 10.1111/gcb.13821