Lost freshwater may double climate change effects on agriculture

Dec 17, 2013 by Rob Mitchum
Comparison of the total annual global calories of maize, soybean, wheat, and rice for RCP 8.5 as projected by four sets of ensemble simulations. Credit: Elliott et al, 2013.

A warmer world is expected to have severe consequences for global agriculture and food supply, reducing yields of major crops even as population and demand increases. Now, a new analysis combining climate, agricultural, and hydrological models finds that shortages of freshwater used for irrigation could double the detrimental effects of climate change on agriculture.

Given the present trajectory of greenhouse gas emissions, agricultural models estimate that will directly reduce food production from maize, soybeans, wheat and rice by as much as 43 percent by the end of the 21st century. But hydrological models looking at the effect of warming climate on freshwater supplies project further agricultural losses, due to the reversion of 20 to 60 million hectares of currently irrigated fields back to rain-fed crops.

"It's a huge effect, and an effect that's basically on the same order of magnitude as the direct effect of climate change," said Joshua Elliott, a research scientist with the Computation Institute's Center for Robust Decision Making on Climate and Energy Policy (RDCEP), Argonne National Laboratory, and lead author of the paper. "So the effect of limited irrigation availability in some regions could end up doubling the effect of climate change."

The research was led by Elliott and colleagues from the Agricultural Model Intercomparison and Improvement Project (AgMIP), as part of the Inter-Sectoral Impacts Model Intercomparison Project (ISI-MIP). The paper is among 12 featured in a special feature dedicated to ISI-MIP research in Proceedings of the National Academy of Sciences, published online December 16.

Agricultural models and hydrological models both incorporate the influence of climate, but are designed by different scientific communities for different purposes. While agricultural models simulate how temperature, precipitation and other climate factors may alter the yield for various crops, hydrological models seek to estimate water-related characteristics such as stream flow, water availability, and storm runoff.

The two types of models overlap in estimating the amount of water used for agricultural irrigation, by far the largest human use of freshwater in the world. But when Elliott and colleagues fed each type of with the same climate model forecasts, the models produced dramatically different predictions about the future demand for freshwater irrigation

The researchers discovered discrepancies in how hydrological models incorporate processes such as the carbon cycle and crop water productivity when compared to agricultural models – a finding that will help make existing models more accurate.

"This is absolutely the first study in which a multi-model ensemble of hydrological models was compared to a multi-model ensemble of crop models," Elliott said. "Several modeling groups have already changed the way that they are modeling the hydrological cycle with respect to crops because of the results of this paper."

The comparison also produced new insight about the potential agricultural consequences of climate change. Due to climate change alone, the models predicted a loss of between 400 and 2600 petacalories of , 8 to 43 percent of present day levels. But due to the decline in freshwater availability – and the associated conversion of irrigated cropland to rain-fed – the models predict an additional loss of 600 to 2900 petacalories, the researchers discovered.

However, while the models predict freshwater shortages in some areas of the world, such as the western United States, India and China, other regions may end up with a surplus of freshwater. Redistributing that excess water to restore or add irrigation to rain-fed crop areas could dampen some of the consequences of climate change upon irrigation and agriculture, Elliott said.

"We found that maximal usage of available surplus freshwater could end up ameliorating between 12 and 57 percent of the negative direct effects of climate change on food production," Elliott said. "However, there are lots of different political, economic and infrastructural reasons why you would consider that to be overly optimistic."

The results are among several major findings reported in the ISI-MIP special issue of PNAS by the AgMIP group, which conducted a "fast-track" exercise to generate new knowledge about on agriculture for the Fifth Assessment Report of the Intergovernmental Panel on Climate Change.

"Understanding the climate change implications of freshwater availability is key to the future food security goals of society," said Cynthia Rosenzweig, co-primary investigator of AgMIP and co-author of the paper. "The rigorous AgMIP multi-model approach is enabling advances in research on how climate change will affect agriculture worldwide and water is a vital component."

Explore further: Recognizing the elephant in the room: Future climate impacts across sectors

More information: "Constraints and potentials of future irrigation water availability on agricultural production under climate change." Joshua Elliott, Delphine Deryng, Christoph Müller, et al. PNAS December 16, 2013, DOI: 10.1073/pnas.1222474110

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mememine69
2.5 / 5 (8) Dec 17, 2013
Billions of children subjected to 30 years of needless CO2 panic have been condemned to the greenhouse gas ovens of an exaggerated crisis. Get ahead of the curve;
*Occupywallstreet now does not even mention CO2 in its list of demands because of the bank-funded and corporate run carbon trading stock markets ruled by politicians.
It's time you lazy copy and paste news editors stopped riding the climate blame exaggeration and renounced it now before history denounces you for this needless panic.
#Not one single IPCC warning agrees beyond; "could be" a crisis and have NEVER said or agreed it WILL be a crisis and not once did you news repeaters ever mention this fact that could have ended this costly debate 30 years ago.# Nice work girls, you clowns have done to journalism and science itself what naughty naughty priests and suicide bombers did for world religions.
The only crisis you remaining blamers and doomers have to worry about is how your grand kids will explain to their kids how you so easily and with such sickening childish glee (at the mere grunt of a consensus headline) sentenced them all to a CO2 climate crisis.
Maggnus
3.3 / 5 (7) Dec 17, 2013
Wow this one is off on a tangent! "Condemned to the greenhouse gas ovens" are they? "Needless panic" is it? Have they recently reduced your meds? You should ask them to either return you to your original dose, or request they up the anti-psychotic.

I sure hope you don't have kids Skippy, the gene pool is already shallow enough.
ScooterG
2.1 / 5 (7) Dec 17, 2013
"Several modeling groups have already changed the way that they are modeling the hydrological cycle with respect to crops because of the results of this paper."

This statement pretty-well sums up AGW modeling - take models based on junk science, modify them to suit the desired outcome, then everyone on the AGW payroll edifies the Hell out of each other.
Maggnus
3.3 / 5 (7) Dec 17, 2013
ANd now scooter's back! Hey dumdum, how you been? I see you haven't tried to learn anything new. Same old mis-representations, same old "they are colluding against us" conspiracy crap.

Hey Scooter, is it still the case that you don't claim to belive there is a conspiracy because you don't use the word "conspiracy" when your describing the conspiracy you think all scientists are a part of?
ReduceGHGs
2.3 / 5 (6) Dec 17, 2013
There's no reasonable doubt among those that actively study climates; we are warming the planet and the consequences are not good. But ask yourself... "What am I doing about it?" Apathy advocates business-as-usual. Please join the efforts to reduce global emission.
www.ExhaustingHabitability.com
Shootist
2.6 / 5 (5) Dec 17, 2013
Wow this one is off on a tangent! "Condemned to the greenhouse gas ovens" are they? "Needless panic" is it? Have they recently reduced your meds? You should ask them to either return you to your original dose, or request they up the anti-psychotic.

I sure hope you don't have kids Skippy, the gene pool is already shallow enough.


Of course it's needless. The climate changes. That's what climates do.

Otherwise, "the polar bears will be fine"- Freeman Dyson
ScooterG
2.3 / 5 (6) Dec 17, 2013
ANd now scooter's back! Hey dumdum, how you been? I see you haven't tried to learn anything new. Same old mis-representations, same old "they are colluding against us" conspiracy crap.

Hey Scooter, is it still the case that you don't claim to belive there is a conspiracy because you don't use the word "conspiracy" when your describing the conspiracy you think all scientists are a part of?


Give your hallowed AGW researchers a little credit - they don't need to collude nor conspire to know how best to maximize their earnings.

Your childish habit of name-calling dovetails nicely with the idiocy that has come to define so much of AGW - keep up the good work.
alfie_null
3 / 5 (4) Dec 18, 2013
Give your hallowed AGW researchers a little credit - they don't need to collude nor conspire to know how best to maximize their earnings.

When you say things like this, it's as if you were opening up a little window into your soul. Letting us all see what's squirming around down there: "If researchers are claiming something I don't like to hear, they must be telling lies. And if they are telling lies, it must be for some reason. I'll imagine it's a reason I can easily concur with."

That you disagree with them doesn't mean they lie. And, hard as this might be for you to understand, it doesn't mean they are chasing after money. As has been mentioned before, for someone with that caliber of intellect, there are far easier ways to become wealthy.
ScooterG
2.3 / 5 (6) Dec 18, 2013
Give your hallowed AGW researchers a little credit - they don't need to collude nor conspire to know how best to maximize their earnings.

When you say things like this, it's as if you were opening up a little window into your soul. Letting us all see what's squirming around down there: "If researchers are claiming something I don't like to hear, they must be telling lies. And if they are telling lies, it must be for some reason. I'll imagine it's a reason I can easily concur with."

That you disagree with them doesn't mean they lie. And, hard as this might be for you to understand, it doesn't mean they are chasing after money. As has been mentioned before, for someone with that caliber of intellect, there are far easier ways to become wealthy.


Nice try, but 100% wrong - every word of it.
Maggnus
2.8 / 5 (4) Dec 19, 2013
Nice try, but 100% wrong - every word of it
Hahahaha, geepers you tell him Scooter!

Cause dey all be CONSPIRATORING an all dat! All dems SCIENTISTS all LYING and CONSPIRATORING an stuff! An getting PAID and getting GRANTS an all dat!

You're a moron ScooterG.
Jimee
1 / 5 (1) Dec 23, 2013
Fear and loathing in oil and coal land. How with the deniers distort reality next?