National Aeronautics and Space Administration

National Aeronautics and Space Administration

Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadena, California

www.nasa.gov

PI Simon Hook (JPL)SCIENCE LEAD Joshua B. Fisher (JPL)SCIENCE TEAM Rick Allen (U. Idaho)

Martha Anderson (USDA)Andy French (USDA)Chris Hain (UMD)Glynn Hulley (JPL)Eric Wood (Princeton U.)

© 2014 California Institute of Technology. Government sponsorship acknowledged.

E C O S T R E S S K E Y S C I E N C E Q U E S T I O N S

1. HOW IS THE TERRESTRIAL BIOSPHERE RESPONDING TOCHANGES IN WATER AVAILABILITY?

2. HOW DO CHANGES IN DIURNAL VEGETATION WATERSTRESS IMPACT THE GLOBAL CARBON CYCLE?

3. CAN AGRICULTURAL VULNERABILITY BE REDUCED THROUGHADVANCED MONITORING OF AGRICULTURAL CONSUMPTIVEUSE AND IMPROVED DROUGHT DETECTION?

E C O S T R E S S S C I E N C E O B J E C T I V E S

1. IDENTIFY CRITICAL THRESHOLDS OF WATER USE AND WATERSTRESS IN KEY CLIMATE SENSITIVE BIOMES (E.G.,TROPICAL/DRY TRANSITION FORESTS, BOREAL FORESTS);

2. DETECT THE TIMING, LOCATION, AND PREDICTIVE FACTORSLEADING TO PLANT WATER UPTAKE DECLINE AND/ORCESSATION OVER THE DIURNAL CYCLE;

3. MEASURE AGRICULTURAL WATER CONSUMPTIVE USE

GLOBALLY AT SPATIOTEMPORAL SCALES APPLICABLE TOIMPROVING DROUGHT ESTIMATION ACCURACY.

E C O S T R E S S C O R E S C I E N C E H Y P O T H E S E S

H1: THE WUE OF A CLIMATE SENSITIVE HOTSPOT IS SIGNIFICANTLYLOWER THAN NON-HOTSPOTS OF THE SAME BIOME TYPE;

H2: DAILY ET IS OVERESTIMATED WHEN EXTRAPOLATING FROMMORNING-ONLY OBSERVATIONS;

H3: REMOTELY SENSED ET MEASURED AT THE FIELD SCALE WILLIMPROVE DROUGHT PREDICTION OVER MANAGED ECOSYSTEMS.

A P P R O A C H

What we need: accurate, high spatial, high temporal, diurnal cycle, global, ET.

100

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Landsat 7 – 60 m

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MODIS – 1 km

MODIS – 1 km Landsat 7 – 60 m

JUN JUL AUG SEP OCT

Month

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Evap

otra

nspi

ratio

n (W

m-2

)Measured (FLUXNET)LandsatECOSTRESS

Eva

po

tran

spir

atio

n

6 AM 12 PMDiurnal Cycle

6 PM

Stomata close to conserve water

Water Stress Drives Plant Behavior

The International Space Station (ISS)

Gray shading represents mean diurnal variation in ET over 14-days. The afternoon decline in ET is related to water stress (clear day).

I Xylem refilling after initial water release. II ET at maximum/potential rate in the morning. III Stomata shut down water flux in the afternoon.

IV ET resumes at maximum/potential in early evening when demand is reduced.

COMMENTARY10.1002/2016WR020175

The future of evapotranspiration: Global requirementsfor ecosystem functioning, carbon and climate feedbacks,agricultural management, and water resourcesJoshua B. Fisher1 , Forrest Melton2, Elizabeth Middleton3, Christopher Hain4,5, Martha Anderson6,Richard Allen7, Matthew F. McCabe8 , Simon Hook1, Dennis Baldocchi9 , Philip A. Townsend10,Ayse Kilic11, Kevin Tu12 , Diego D. Miralles13 , Johan Perret14, Jean-Pierre Lagouarde15,Duane Waliser1 , Adam J. Purdy1 , Andrew French16 , David Schimel1, James S. Famiglietti1,Graeme Stephens1 , and Eric F. Wood17

1Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA, 2NASA Ames Research CenterCooperative for Research in Earth Science in Technology, Moffett Field, California, USA, 3NASA Goddard Space FlightCenter, Greenbelt, Maryland, USA, 4NASA Marshall Space Flight Center, Huntsville, Alabama, USA, 5NOAA NationalEnvironmental Satellite, Data, and Information Service, College Park, Maryland, USA, 6U.S. Department of Agriculture,Beltsville, Maryland, USA, 7University of Idaho, Kimberly, Idaho, USA, 8King Abdullah University of Science andTechnology, Thuwal, Saudi Arabia, 9University of California, Berkeley, California, USA, 10University of Wisconsin, Madison,Wisconsin, USA, 11University of Nebraska-Lincoln, Lincoln, Nebraska, USA, 12DuPont Pioneer, Johnston, Iowa, USA, 13GhentUniversity, Ghent, Belgium, 14EARTH University, San, Jos!e, Costa Rica, 15INRA, ISPA UMR 1391, Villenage D’Ornon, France,16U.S. Department of Agriculture, Maricopa, Arizona, USA, 17Princeton University, Princeton, New Jersey, USA

Abstract The fate of the terrestrial biosphere is highly uncertain given recent and projected changes inclimate. This is especially acute for impacts associated with changes in drought frequency and intensity onthe distribution and timing of water availability. The development of effective adaptation strategies forthese emerging threats to food and water security are compromised by limitations in our understanding ofhow natural and managed ecosystems are responding to changing hydrological and climatological regimes.This information gap is exacerbated by insufficient monitoring capabilities from local to global scales. Here,we describe how evapotranspiration (ET) represents the key variable in linking ecosystem functioning, car-bon and climate feedbacks, agricultural management, and water resources, and highlight both the out-standing science and applications questions and the actions, especially from a space-based perspective,necessary to advance them.

1. Introduction

The response of the terrestrial biosphere to changes in climate remains one of the largest sources ofuncertainty in climate projections [Friedlingstein et al., 2014]. Tightly coupled to the water cycle, ecosys-tems can act as either carbon sinks (photosynthesis, primary production) or carbon sources (respiration,decomposition, mortality, combustion), and provide climate feedbacks through latent heat fluxes, albe-do, and water cycling. However, the water cycle is rapidly changing, resulting in greater variance andmore extremes [Ziegler et al., 2003; Syed et al., 2010]. For example, the worst drought in its recorded his-tory struck the Amazon basin in 2005, reversing this long-term carbon sink into a carbon source [Phillipset al., 2009]. In 2010, an even stronger drought hit the Amazon basin, which had not fully recovered fromthe impacts of the earlier event, and 2015 saw yet another recurrence [Lewis et al., 2011; Saatchi et al.,2013; Jim!enez-Mu~noz et al., 2016]. The United States Midwest also experienced its worst drought in deca-des in 2011, followed by an even stronger one in 2012, which impacted 80% of US agriculture; in parallel,a multiyear drought from 2012 to 2015 along the West coast significantly impacted food production forthe entire country [Long et al., 2013; Mallya et al., 2013; AghaKouchak et al., 2014; Wolf et al., 2016]. Over-all these patterns of extreme drought have been mirrored throughout nearly all major terrestrial vegetat-ed biomes of the world, as well as in the key food production regions of every inhabited continent [Ciaiset al., 2005; Soja et al., 2007; Cook et al., 2010; Schwalm et al., 2012; Fisher et al., 2013b; van Dijk et al.,2013; Famiglietti, 2014].

Key Points:! ET science and applications have

significantly advanced across a widearray of fields over the past severaldecades! Critical outstanding ET-based

research and applied sciencequestions from local to global scalesremain due to deficiencies in ourobservational capabilities! National and international research

priorities should include ET-focusedsatellite observational investmentsand programs

Correspondence to:J. B. Fisher,jbfisher@jpl.nasa.gov

Citation:Fisher, J. B., et al. (2017), The future ofevapotranspiration: Globalrequirements for ecosystemfunctioning, carbon and climatefeedbacks, agricultural management,and water resources, Water Resour.Res., 53, doi:10.1002/2016WR020175.

Received 23 NOV 2016Accepted 11 FEB 2017Accepted article online 11 MAR 2017

VC 2017. The Authors.

This is an open access article under theterms of the Creative CommonsAttribution-NonCommercial-NoDerivsLicense, which permits use anddistribution in any medium, providedthe original work is properly cited, theuse is non-commercial and nomodifications or adaptations aremade.

FISHER ET AL. THE FUTURE OF EVAPOTRANSPIRATION 1

Water Resources Research

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