Warming raises drought’s threat to California

Warming raises drought's threat to California

US researchers say climate change, not random chance, is likely to be causing California’s long drought, one of the worst on record.

LONDON, 3 March, 2015 –  Climate change could be driving the sustained Californian drought. Arid spells have been more frequent in the last two decades than in the preceding century. And warmer global temperatures linked to man-made climate change could be at the heart of it.

Right now, California is in the sustained grip of one of its worst-ever droughts. Noah Diffenbaugh of Stanford University in California and colleagues looked at the patterns of precipitation, temperature and drought in the historical record and report in the Proceedings of the National Academy of Sciences that the latest conditions were not just a random outcome.

In a sunlit landscape with a long record of intermittent drought, researchers make such predictions only cautiously. But the Stanford team worked through 120 years of rainfall, snowfall and temperature data to identify connections.

They found that, puzzlingly, the two sets of measurements were not directly connected: for the first 60 or 70 years of the historical record, it could be wet and warm, or cool and dry. But drought was more likely in those years that by chance were both dry and warm.

Doubled risk

“Of course low precipitation is a prerequisite for drought but less rain and snowfall alone don’t ensure a drought will happen. It really matters if the lack of precipitation happens during a warm or a cool year,” said Dr Diffenbaugh.

“We’ve seen the effects of record heat on snow and soil moisture this year in California and we know from this new research that climate change is increasing the probability of those warm and dry conditions occurring together.”

On the flip-a-coin analogy, the weather could be either wet or dry, and cold or hot. So only one time in four, the weather was both hot and dry. For most of the past two decades, years in California have been either warm, or hot.

“Now the temperature coin is coming up tails most years. So even though the precipitation coin is coming up tails only half the time, it means that over the past two decades we have gotten two tails-warm and dry in half the years, compared with only a quarter of years in the preceding century.”

Most populous

Accordingly, drought frequency has doubled. Model simulations suggest that the risk of any year being both warm and dry will continue. More frequent warm years will also increase the probability of multi-year drought.

The present drought is now in its fourth year, and is one of the longest consecutive periods during which conditions are severely dry and severely warm.

And soon California – home to one in eight Americans, and the country’s most populous state – could enter a climate regime in which the risk that every year will be warmer than the 20th century norm will be almost 100%.

The findings, said Dr Diffenbaugh, provide “very strong evidence that global warming is already making it much more likely that California experiences conditions that are similar to what we have already experienced during the current severe drought.” – Climate News Network

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Climate impacts on European farmers’ yields per field

Climate impacts on European farmers’ yields per field

Scientists says changes in temperature and snow or rainfall are key factors in the stagnation of wheat and barley yields across Europe since the early 1990s.

LONDON, 19 February, 2015 – Farmers in Europe have already begun to feel the pinch of climate change as yields of wheat since 1989 have fallen by 2.5% and barley by 3.8% on average across the whole continent.

And two Californian scientists now believe that changes in temperature and snow or rainfall during the last quarter of a century are at least partly to blame.

The pinch may be gentle, but environmental scientists Frances Moore and David Lobell, of Stanford University, believe it is real.

They report in the Proceedings of the National Academy of Sciences that although changes in farming and environmental policies explain much of the stagnation of yields in Europe in the last 25 years, at least 10% of this change could be attributed to climate trends.

Sugarbeet and maize harvests have gone up slightly − and that, too, could be pinned on global warming.

Overall trends

It is no small challenge to find an overall trend to crop yields across a continent that stretches from Scotland to the Black Sea, from northern Norway to Sicily, and over a timescale that embraces floods, droughts, forest fires and heat waves that may or may not have been made worse or more frequent by global warming, but which would have occurred anyway.

The other complication is that, in the same 25 years, the patterns of agricultural subsidy and market demand have also changed.

But the Stanford scientists started with conditions on the farms in the 1980s, when Europe’s farmers were, on average, getting 0.12 more tonnes of wheat and barley per hectare than the year before. Yields per field were rising steadily.

“Agriculture is one of the economic sectors most exposed to climate change impacts”

“If they had continued growing at that rate after 1995, wheat and barley yields would be 30% and 37% higher today, respectively,” they write.

Climate trends could perhaps account for around 10% of the stagnation revealed in the statistics. The remaining change could be put down to economic and political shifts and other factors.

One of these would be that crops had been improving to a point called the biophysical limits: just how much weight of grain could one stalk hold anyway? So some change would be expected, and climate must be a component of that.

To arrive at their conclusion, the two scientists looked at the predictions made for climate change – southern Europe was always expected to become drier, but farmers in moist northern climates could benefit from temperature increases – and the available data, and then applied sophisticated mathematical probability techniques to isolate the possible impact of climate change so far.

Social costs

They have looked at the economic and social challenges of global warming before. Last year, they warned that Europe’s farmers were going to have to adapt to climate change in the 21st century, and Moore and a colleague claimed last month that economists had badly underestimated the economic and social costs of each tonne of carbon added to the levels of CO2 in the atmosphere.

The new research is, they argue, important because “agriculture is one of the economic sectors most exposed to climate change impacts, but few studies have statistically connected long-term changes in temperature and rainfall with yields.

“Doing so in Europe is particularly important because yields of wheat and barley have plateaued since the early 1990s ,and climate change has been suggested as a cause of this stagnation.” – Climate News Network

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Stalagmite links rain reduction to industrial revolution

Stalagmite links rain reduction to industrial revolution

Research shows the explosion of fossil fuel use to power the 19th-century industrial boom began the pattern of lower rainfall affecting the northern tropics. 

LONDON, 17 February, 2015 − Scientists have identified a human-induced cause of climate change. But this time it’s not carbon dioxide that’s the problem − it’s the factory and power station chimney pollutants that began to darken the skies during the industrial revolution.

Analysis of stalagmite samples taken from a cave in Belize, Central America, has revealed that aerosol emissions have led to a reduction of rainfall in the northern tropics during the 20th century.

In effect, the report in Nature Geoscience by lead author Harriet Ridley, of the Department of Earth Sciences at the University of Durham, UK, and international research colleagues invokes the first atmospheric crisis.

Acid rain

Before global warming because of greenhouse gases, and before ozone destruction caused by uncontrolled releases of chlorofluorocarbons, governments and environmentalists alike were concerned about a phenomenon known as acid rain.

So much sulphur and other industrial pollutants entered the atmosphere that raindrops became deliveries of very dilute sulphuric and nitric acid.

The damage to limestone buildings was visible everywhere, and there were concerns – much more difficult to establish – that acid rain was harming the northern European forests.

But even if the massive sulphate discharges of an industrialising world did not seriously damage vegetation, they certainly took a toll on urban human life in terms of respiratory diseases.

Clean-air legislation has reduced the hazard in Europe and North America, but it seems that sulphate aerosols have left their mark.

Researchers in a cave in Belize. Credit: Dr James Baldini/Durham University

Researchers in a cave in Belize.
Image: Dr James Baldini/Durham University

The Durham scientists reconstructed tropic rainfall patterns for the last 450 years from the analysis of stalagmite samples taken from a cave in Belize.

The pattern of precipitation revealed a substantial drying trend from 1850 onwards, and this coincided with a steady rise in sulphate aerosol pollution following the explosion of fossil fuel use that powered the Industrial Revolution.

They also identified nine short-lived drying spells in the northern tropics that followed a series of violent volcanic eruptions in the northern hemisphere. Volcanoes are a natural source of atmospheric sulphur.

Atmospheric pollution

The research confirms earlier suggestions that human atmospheric pollution sufficient to mask the sunlight and cool the upper atmosphere had begun to affect the summer monsoons of Asia, and at the same time stepped up river flow in northern Europe.

The change in radiation strength shifted the tropical rainfall belt, known as the intertropical convergence zone, towards the warmer southern hemisphere, which meant lower levels of precipitation in the northern tropics.

“The research presents strong evidence that industrial sulphate emissions have shifted this important rainfall belt, particularly over the last 100 years,” Dr Ridley says.

“Although warming due to man-made carbon dioxide emissions has been of global importance, the shifting of rain belts due to aerosol emissions is locally critical, as many regions of the world depend on this seasonal rainfall for agriculture.” – Climate News Network

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California is left high and dry by cannabis growers

California is left high and dry by cannabis growers

As California endures its worst drought since records began, illegal marijuana plantations are being blamed for further depleting precious water resources.

MENDOCINO, 4 February, 2015 − Take a flight over the densely forested area in California’s northern coastal region and it’s not hard to spot the marijuana plantations, their bright green plants standing out in clearings in the surrounding vegetation.

But now the big-money cannabis industry is being blamed for adding to water shortage problems caused by a three-year drought that has seriously affected California’s huge agricultural sector.

Although cultivating and using marijuana is illegal under US Federal law, California state law allows marijuana growing – as long as it is for medicinal purposes.

Rules flouted

However, the rules governing who can and cannot grow pot are complex – and openly flouted by thousands of growers, both big and small-time operators.

A report by the California Department of Fish and Wildlife (CDFW) estimates that, in this northern region of the state,  marijuana growing doubled between 2009 and 2012.

Marijuana plants are extremely thirsty, consuming between five and 10 gallons of water per day, depending on the phase of their growing cycle. Officials at the CDFW say that marijuana growers are sucking up precious water resources, exacerbating water shortages and threatening fish in the area’s lakes and streams.

Marijuana growing is particularly prevalent in an area of northern California known as The Emerald Triangle, encompassing Mendocino, Humbolt and Trinity counties. Some estimates say the crop accounts for up to 40% of the region’s economy.

Officials of the CDFW say that the small, well-established marijuana plantations – run by what are described as old time hippies − are not to blame for pumping up excess water.

Illegal marijuana plantations in forest clearings. Image: US Drug Enforcement Agency

Illegal marijuana plantations in forest clearings.
Image: US Drug Enforcement Administration

It is the incomers from outside the area − part of a “green rush” into highly-profitable marijuana growing – that are mainly to blame. These growers are out to make quick profits, and care little about the environment.

Growers of various crops in California are bound by rules stipulating that no more than 10% of the flow of water courses should be diverted for crops, and that such diversions should stop altogether in late summer, when water levels are at their lowest.

The CDFW says the incomers take vast amounts of water in order to harvest their crops as fast as possible. They also use excessive quantities of fertilizer, which leach into water courses, endangering fish stocks and polluting land.

Armed gangs

Fines of up to $8,000 per day are now being imposed for water theft, although monitoring illegal activities is difficult − and, at times, dangerous. Heavily-armed gangs are often involved in the marijuana growing business, and the CDFW has warned that, as the drought continues, conflicts over water resources are likely to increase.

The Emerald Growers Association, a group that represents some of northern California’s marijuana growers, says more regulation is needed to separate the legitimate pot growers from illegal ones.

The drought in California has been going on since 2011 and is described as the worst in the state since records began in the 1850s.

Arguments continue as to whether man-made climate change or natural phenomena are causing the drought.

Although significant amounts of rain last December helped alleviate dry conditions in some parts of the state, experts say more rain is urgently needed to feed watercourses and restock severely depleted aquifers. – Climate News Network

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Chimps’ survival hopes jeopardised by climate change

Chimps’ survival hopes jeopardised by climate change

One of our closest animal relatives is at risk of being wiped out as changing rainfall patterns threaten to destroy its Central African habitat.

LONDON, 30 January, 2015 − Climate change is a challenge for chimpanzees, too. New research warns that a primate subspecies – one of humanity’s closest animal relatives – could become endangered within five years

The threatened subspecies of the common chimpanzee is Pan troglodytes ellioti, and there are only 6,000 remaining individuals, surviving in two populations in Cameroon.

Field biologist Paul Sesink Clee, of Drexel University, US, and colleagues report in BMC Evolutionary Biology that they combined climate, environmental and population data to model how the chimpanzees’ preferred habitats would change with climate under a “business as usual” scenario in which the world went on burning fossil fuels.

Habitat change

Underlying such research is the larger question of how variation in habitat drives evolutionary change: why are there four subspecies of chimpanzee, and how much does geography and habitat have to do with it?

So the scientists made a chimpanzee population map, and imposed it on a map of habitats.

They found two distinct populations of the chimpanzee − one in the mountainous rainforests of western Cameroon, and one in a distinctive region of grassland, forest and woodland in central Cameroon.

Then they simulated how these habitats would change under global warming scenarios by 2020, 2050 and 2080.

“Preliminary projections suggest that rainfall patterns will change dramatically in this region of Africa”

Their findings were that the mountain rainforest habitat would survive, but the lowland dwellers would decline quickly under all scenarios by 2020, and could disappear almost entirely under the worst case scenario by 2080.

Since half of the entire population of Nigeria-Cameroon chimpanzees survive in this habitat, the suggestion is that the chimpanzees are particularly vulnerable to climate change.

Severely affected

The researchers did not take into account the opportunities for the chimpanzees to migrate, or to adapt to new circumstances. They point out that Central Africa in particular, and the continent in general, is likely to be severely affected by climate change.

“Preliminary projections suggest that rainfall patterns will change dramatically in this region of Africa, which will result in significant alterations of forest and savanna habitats,” the report says.

“Models of global climate change also have been used to show that 30% of plant and animal species are at risk of extinction if the rise in mean global temperature exceeds 1.5°C − an increase that is nearly certain to occur under future climate scenarios.” – Climate News Network

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Climate renews famine risk to Africa’s Sahel

Climate renews famine risk to Africa’s Sahel

With population increasing and food demand far outstripping supply, the Sahel is vulnerable to a new humanitarian crisis − and researchers warn that rising temperatures will only make matters worse.

LONDON, 20 October, 2014 − The Sahel, the arid belt of land that stretches from the Atlantic to the Red Sea and separates the Sahara desert from the African savanna, is no stranger to drought and famine.

Now scientists in Sweden say the Sahel faces another humanitarian crisis even than in the recent past − with the changing climate partly responsible.

Writing in the journal Environmental Research Letters, the researchers from Lund University say people in the Sahel need more food, animal feed and fuel every year. But demand, which has more than doubled over a recent 10-year period, is growing much faster than supply.

Fewer resources

Data from 22 countries shows the result: fewer resources per capita and a continued risk of famine in areas with low primary production – that is, the availability of carbon in the form of plant material for consumption as food, fuel and feed.

Human numbers are part of the reason. Between 2000 and 2010, the population of the Sahel grew from 367 million to 471 million people − an annual rise of 2.2% over the decade.

But crop production remained essentially unchanged, so the margin between supply and demand for primary production is shrinking every year, while the Sahel’s population is forecast to total nearly a billion people by 2050.

Children's graves at a refugee camp in Kenya during the famine in 2011 Image: Andy Hll/Oxfam via Wikimedia Commons
Children’s graves at a Kenyan refugee camp during the 2011 famine
Image: Andy Hall/Oxfam via Wikimedia Commons

Some studies suggest that modern plant strains can withstand the effects of drought better than traditional cultivars, although this was not a focus of the Lund team.

They were mainly concerned with the staple crops grown regionally − such as sorghum and millet, which are used as food for people, with the residues used as fodder for livestock − and with the dry woodlands that provide fuel.

They used remote analysis and satellite images to calculate annual crop production in the 22 countries they studied, and compared the figures with data on population growth and consumption of food, animal feed and fuel. This relationship helps to measure a region’s vulnerability.

The study shows that 19% of the Sahel’s total primary production in 2000 was consumed. Ten years later, consumption had increased to 41%.

Reduced harvest

It says several forecasts suggest that harvests will be reduced as a result of the higher air temperatures the region is now experiencing, even though climate change is predicted to result in the Sahel receiving more rain in future.

So, the researchers say, climate change can only increase the vulnerability of the Sahel.

Asked by the Climate News Network whether higher air temperatures alone were likely to cancel the gains from increased rainfall, one of the study’s authors, Hakim Abdi, a doctoral student in physical geography and ecosystem science at Lund, said: “The short answer is yes. Studies indicate that higher temperatures offset both increased rainfall and CO2 fertilisation.

“Additionally, a recent study found that increase in future rainfall in the Sahel, a region where the soil generally receives little nutrient input and is over-exploited, causes nutrient leaching, and hence induces nitrogen stress.

“When we were in our study site in North Kordofan in Sudan, the most common complaint we received from the villages we visited was the lack of water.

“I think that if a drought occurs with an impact that matches or exceeds the ones in 1972/73 or 1982/83, we will see serious consequences − worse impacts than past ones.” − Climate News Network

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Australia gets early blast of more extreme heat

Australia gets early blast of more extreme heat

Summer has come early across much of Australia – and as temperatures soar to record seasonal levels in many areas, the bushfire season has started well ahead of schedule.

LONDON, 14 October, 2014 − It’s the time of year when many Australians start to think about eating outdoors or heading for the beach after work. Early spring, and the temperatures are rising – particularly this year.

The Australian Government’s Bureau of Meteorology (BOM) says maximum temperatures in September across much of the country were higher than average, with central and south-western areas experiencing their warmest September on record.

Australia is considered to be particularly vulnerable to the effects of a climate change, and 2013 was the country’s hottest year since records began, with average temperatures 1.2˚C above the long-term average.

In one seven-day period in early January last year, record national average temperatures exceeded 39˚C.

Unprecedented levels

September started off cool in Sydney, Australia’s most populated city, but then heated up to unprecedented levels for this time of year. For the first time, temperatures climbed to more than 32˚C for two consecutive days in the month.

Meanwhile, overall September rainfall was 27% below the monthly average − and the dry conditions mean the bushfire season has come early. The south of the island of Tasmania has fared particularly badly, with fires fuelled by dry conditions and high winds.

Areas round Sydney and throughout New South Wales – the country’s most populous state − have also been hit by bushfires, with fire warnings going out to more than a million homeowners.

Despite growing evidence that human-induced climate change is a major reason for Australia heating up, the Liberal-National coalition government led by Prime Minister Tony Abbott has taken little action on the issue.

It has abolished a carbon tax introduced by the previous Labour government, abolished a Climate Commission that gave advice on the impact of warming, and is seeking to downgrade modest renewable energy targets.

Polluting fuel

Australia is one of the world’s leading producers of coal – the most polluting fuel, which is responsible for a significant portion of climate changing greenhouse gas emissions (GHGs). The country’s per capita GHG emissions are among the highest in the world.

A recent report on Australia’s climate, produced by BOM and the Commonwealth Scientific and Industrial Research Organisation (CSIRO), the national science agency, predicts temperatures rising across the country by between 0.6˚C and 1.5C by 2030, compared with the rise of 0.6˚C between 1910 and 1990.

The report says: “Data and analysis from BOM and CSIRO show further warming of the atmosphere and oceans in the Australian region. . . this warming has seen Australia experiencing warm weather and extreme heat, and fewer cool extremes.

“There has been an increase in extreme fire weather, and a longer fire season, across large parts of Australia.” – Climate News Network

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Solar dimming reflects complexity of climate change

Solar dimming reflects complexity of climate change

Reduced monsoon rainfall and increased river flow are two extremes that new research has linked to man-made impacts on climate caused by air pollution.

LONDON, 13 October, 2014 − Two separate studies have confirmed the extent of human influence on climate change – and, for once, carbon dioxide is not the usual suspect.

One team has just found that air pollution dimmed the skies of northern Europe, reflected sunlight back into space, reduced evaporation, and increased river flow.

The second group reports that similar aerosol pollution had a quite different effect on the Asian monsoons: in the second half of the 20th century, the darkening skies reduced temperatures and cut the summer monsoon rainfall by 10%.

The two seemingly contradictory findings underscore two clear conclusions. One is that climate science is complex. The other is that human activity clearly influences the climate in different ways.

Worldwide concern

Both studies are concerned with an era when there was, worldwide, more concern about choking smog, sulphuric aerosol discharges and acid rain than about man-made global warming. They also both match complex computer simulation with observed changes in climate during the second half of the 20th century

Nicola Gedney, a senior scientist at the UK’s Meteorological Office, and colleagues report in Nature Geoscience that she and colleagues looked at the growth in aerosol pollution, especially in the Oder river catchment area of central-eastern Europe, that followed the increased burning of sulphurous coal in Europe right up till the late 1970s.

The consequence of that burning was a reduction in sunlight over the hemisphere. But this began to reverse with clean air legislation and a widespread switch to cleaner fuels. River flows, which had been on the increase, were reduced.

“We estimate that, in the most polluted central Europe river basin, this effect led to an increase in river flow of up to 25% when the aerosol levels were at their peak, around 1980,” Dr Gedney said. “With water shortages likely to be one of the biggest impacts of climate change in the future, these findings are important in making projections.”

Aerosol pollution

Meanwhile, a group led by Debbie Polson, a researcher in the University of Edinburgh’s School of Geosciences, Scotland, focused on aerosol pollution and the Asian summer monsoons, which provide four-fifths of the annual rainfall of the Indian subcontinent.

They report in Geophysical Research Letters that they calculated annual summer rainfall between 1951 and 2005, used computer simulations to quantify the impact of increasing aerosol emissions and greenhouse gases during that time, and factored in natural variations, such as volcanic discharges.

They found that, overall, levels of rain during the monsoon fell by 10%, and this change could only be explained by the influence of aerosols from car and factory exhausts.

“This study has shown for the first time that the drying of the monsoon over the past 50 years cannot be explained by natural climate variability, and that human activity has played a significant role in altering the seasonal monsoon rainfall on which billions of people depend,” Dr Polson said. – Climate News Network

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Oxford is rewriting ancient weather record books

Oxford is rewriting ancient weather record books

New data added to the unique archive documenting Oxford’s weather since 1767 shows that the university city has just had its second driest September on record – following close on its wettest January.

LONDON, 8 October, 2014 – Several parts of the world like to claim that their unpredictable weather allows you to experience spring, summer, autumn and winter in the space of a single day. The city of Oxford, in the English Midlands, cannot make that boast, but it has broken a surprising number of weather records in a fairly short time.

In its latest bout of meteorological exuberance, Oxford has just had its second driest September since records began almost 250 years ago. It recorded 4.1mm of rainfall over last month, with 1929 the only previous year to have had a month with a lower total − just 2.5mm.

This follows hard on the heels (climatically speaking, at least) of the first month of 2014, which was, by contrast, the wettest January the city has recorded, with total rainfall of 146.9 mm − almost three times the normal and 35 times September’s paltry figure.

Rainiest stretch

Go back a little further, though, for wet weather that really meant business: the nine months from 1 April to 31 December 2012 proved the rainiest nine-month stretch in Oxford’s recorded experience.

Yet the people of Oxford might at that point have been lulled into expectations of balmier weather, because 2011 had turned out to be the city’s joint second-warmest year on record. Six of the top 10 warmest years recorded have occurred since 2000, the warmest being 2006.

Oxford, home of the oldest university in the English-speaking world, knows the details of its weather peaks and troughs so well because it possesses a unique archive.

The Radcliffe Meteorological Station, based at Oxford University’s Green Templeton College and maintained by the university’s School of Geography and the Environment, holds the longest series of temperature and rainfall records for one site in Britain, with records dating back to 1767.

Of nearly 3,000 monthly records since Oxford’s measurements began, only 30 have been drier than last month. This puts September 2014 in the top 1% of the city’s driest ever months.

Dr Ian Ashpole, who collects the daily measurements for Radcliffe, said of the latest record to fall: “Based on analysis of variability around the mean September rainfall over the last 248 years, we can say that no Septembers since 2000 have been unusually wet, but three have been unusually dry.”

Emerging trend

Only one of the other 30 driest months has occurred in the autumn (September to November); 14 have been in spring (March to May), eight in summer (June to August), and the remaining seven during the winter. Four of the driest months have occurred this century.

This year’s September record may be part of an emerging trend in the month since 2000. The 248-year long-term average for September is 60mm, but since the turn of the century 12 have been below this average, including six under 50% of expected rainfall. Only two years have been above the 60mm average − 2008 (72.9mm) and 2006 (90.8mm).

September 2014’s temperature was not quite as extreme as the low rainfall, but still came in at equal seventh (with 1998) at 15.9°C, compared with the long-term average of 13.7°C. Five of the warmest eight Septembers since 1767 have been recorded since 1998.

However, the data from Radcliffe applies only to the city of Oxford and a short distance around it, and can tell us nothing about weather elsewhere in the UK or further afield. – Climate News Network

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Warming will leave drought-hit California reeling

Warming will leave drought-hit California reeling

Researchers in the US warn that climate change could worsen California droughts by drastically reducing water flow from the Sierra Nevada mountains − and also threatens the extinction of a rare species of fish.

LONDON, 16 September, 2014 − Things could soon get worse for drought-hit California. New research predicts that, by the close of the century, global warming could have reduced the flow of water from the Sierra Nevada mountains by at least a quarter.

Michael Goulden, associate professor of earth system science at the University of California Irvine, and Roger Bales, director of the Sierra Nevada Research Institute at the University of California Merced, publish their alarming findings in the Proceedings of the National Academy of Sciences.

Plant growth

Their research looked not at the long-term projections for precipitation in the US south-west, but simply at the effect of higher average temperatures on plant growth.

Mountains in many ways mimic hemispheres: just as trees become more stunted at higher latitudes, so they get smaller and less frequent at higher altitudes. Temperature ultimately controls plant growth.

But a projected warming of 4.1°C by 2100 would make a big difference to plant growth in the Arctic tundra and around the present alpine treeline everywhere in the world.

The scientists contemplated snow and rain conditions in the King’s River Basin in the Sierra Nevada range. They looked at how much flows downstream to local communities, and how much goes back into the atmosphere as water vapour. Then they did their sums.

They calculated that the 4.1°C temperature rise in the region would increase the density of vegetation at high elevations, with a 28% increase in evapotranspiration − the process that draws water up through the roots to the leaves, and then releases it as vapour through the pores. And what was true for one river basin, they thought, should be true for the whole area. River run-off could drop by 26%.

“Scientists have recognised for a while that something like this was possible, but no one has been able to quantify whether it could be a big effect,” said Professor Goulden. “It’s clear that this could be a big effect of climate warming and that managers need to recognise and plan for the possibility of increased water losses from forest evaporation.”

Endangered fish

MEANWHILE, climate change threatens to wipe out an endangered species of fish in a remote area of Nevada.

The Devils Hole pupfish (Cyprinodon diabolis) is not just rare, it is very rare: the population has fallen as low as 35 individuals. It lives in the geothermally-warmed waters of a limestone cavern in the Devils Hole in the Mojave desert, and its existence was probably always precarious. The fish are little more than 2cms long, iridescent blue, and they have made their home in the upper 25 metres of the cavern’s waters for at least 10,000 years.

Devils Hole pupfish are only 2cms long Image: Nevada Fish & Wildlife Office

Devils Hole pupfish are only 2cms long
Image: Nevada Fish & Wildlife Office via Wikimedia Commons

But Mark Hausner, a hydrogeologist at the Desert Research Institute in Las Vegas, Nevada, and colleagues report in the journal Water Resources Research that there is only a 10-week window in which the water temperatures are optimal, and there is enough food available, for new larvae to hatch.

Climate change is bringing the already-warm water to dangerous temperature levels, and this has already shortened by at least one week the brief opportunity to restore the population. When counts began in 1972, there were more than 500 of the fish. A decade ago there were 171, and at the last count there were only 92.

“This is a fish that does live in a fishbowl, an incredibly hostile fishbowl, and you can’t move the fishbowl,” said one of the report’s authors, Scott Tyler, professor in the Department of Geological Sciences and Engineering at the University of Nevada, Reno. “This is a species that can’t adapt or change or leave to go to a better environment.” − Climate News Network

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