Observing Earth from Above
JOSHUA B. FISHER & GREGORY R. GOLDSMITH
CHAPMAN UNIVERSITY
Supported by: NASA ECOSTRESS Science and Applications Team (ESAT) (80NSSC23K0309)
An Introduction to Water-Use Efficiency
Gregory R. Goldsmith
April 10, 2024
Chapman University
Orange California
Learning Objectives
At the end of this class, you should be able to:
-Explain the basic methods, as well as their limitations, used to measure water use efficiency.
-Practice interpreting water-use efficiency to draw appropriate conclusions about how varies over space and time.
-Identify ways in which water-use efficiency can be used to address research questions.
Water-Use Efficiency
Water-use efficiency is a measure of how much carbon plants fix through photosynthesis per unit water lost through transpiration.
Water-Use Efficiency (WUE)
How much carbon do plants fix per unit water lost?
Photosynthesis or Gross Primary Productivity (Carbon Fixed)
(Evapo)Transpiration (Water Lost)
WUE =
Photosynthesis (Carbon Fixation) Uses Sun, H2O, & CO2 to Make Sugars
Sun
H2O
CO2
H2O
O2
Product
Sugars, that can either be consumed or converted into starch, cellulose (wood), waxes, etc.
Byproducts
Transpiration (Water Loss) is the Consequence of CO2 Uptake
H2O
CO2
In this image of the surface of a leaf, you can see the pores (called stomata) where gas exchanged between the leaf and the atmosphere.
Not All Sugar Is Produced Equally!
C3 - Photosynthesis
C4 - Photosynthesis
CAM - Crassulacean Acid Metabolism
Plants Have Evolved Different Photosynthetic Pathways to Photosynthesize While Conserving Water!
Tropical Dry Forest in Yucatan Peninsula
Credit: Fernando Tomas
Dr. Jorge Maximiliano Uuh-Sonda
Instituto Tecnologico de Sonora
Plants Vary in their Rates of Photosynthesis
Photosynthesis (g m-2 30 min1)
Uuh-Sonda et al. (2021)
Plants Vary in their Rates of Transpiration
Evapotranspiration (mm 30 min1)
Uuh-Sonda et al. (2021)
Variation in Photosynthesis and Transpiration Means Changes in WUE
Uuh-Sonda et al. (2021)
Water-use Efficiency (WUE)
Water-Use Efficiency Varies in Cultivars of Cacao
Dra. Eleinis Ávila-Lovera
University of Utah
Cultivar (Different varieties of Cacao)
Water-Use Efficiency Varies Seasonally and Among Cultivars of Cacao
Rainy Season
Dry Season
Water-use efficiency
Four Methods for Estimating Water-Use Efficiency
Leaf Gas Exchange
Leaf Stable Isotopes
Flux Towers
Remote Sensing
Scale (leaf-to-planet)
Many Definitions of Water-Use Efficiency
Many Definitions of Water-Use Efficiency
≠
Many Definitions of Water-Use Efficiency
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≠
Calculating Water-Use Efficiency
With both evaporation and transpiration
With only transpiration and no evaporation
GPP/Transpiration
GPP/Evapotranspiration
ECOSTRESS Product Levels
L1 – Calibrated Radiometry
L2 – Land-Surface Temperature and Emissivity; Cloud Mask
L3 – Evapotranspiration (various versions)
L4 – Water-Use Efficiency; Evaporative Stress Index (various versions)
ECOSTRESS Estimate of Water-Use Efficiency
The technical specifications for each remote sensing “product” are laid out in Algorithm Theoretical Basis Documents (ATBDs):
-Algorithm
-Data sources
-Masks or flags for quality control
-Metadata
ECOSTRESS Estimate of Water-Use Efficiency
Gross Primary Productivity (Carbon Gained)
MODIS (Moderate Resolution Imaging Spectroradiometer) at 1 km Resolution
ECOSTRESS Estimate of Water-Use Efficiency
Evapotranspiration (Water Lost)
ECOSTRESS Daily ET L3 Product at 70 m resolution
ECOSTRESS Estimate of Water-Use Efficiency
What considerations (limitations) need to be accounted for when using ECOSTRESS WUE?
Applications of Water-Use Efficiency
Forests of Switzerland
Brandon Bernardo (Chapman ’21)
Graduate Student at University of Southern California
Forest Composes 30% of Switzerland – Heavily Managed for Extraction
How do we advise forest managers to address global change?
Warming
Drought
CO2
Land-Use Change
Pollution
Impacts of Global Change on Water Use Efficiency
For each of the factors, consider whether you think it will increase or decrease water-use efficiency and why?
Warming
Drought
CO2
Land-Use Change
Pollution
Gross Primary Productivity (Carbon Fixed)
(Evapo)Transpiration (Water Lost)
WUE =
Long-Term Mean Summer Water-Use Efficiency in Swiss Forests
WUE
(g C kg-1 H2O)
White dots are a “mask” applied to pixels not classified as forest
Temperature
R = 0.38
p < 0.001
Precipitation
R = -0.20
p = 0.01
Anthropogenic Nitrogen Deposition (Air Pollution)
R = 0.18
p = 0.03
Key Points
-Water-use efficiency measures the coupled use of water and carbon by plants.
-Interpretation of water-use efficiency is complicated: we need to know whether photosynthesis, transpiration, or both, are changing. Moreover, transpiration varies with humidity, which can make comparisons challenging.
-Water-use efficiency is particularly interesting in agricultural settings, where we wish to maximize yield (growth through photosynthesis) and minimize water use.
Supported by: NASA ECOSTRESS Science and Applications Team (ESAT) (80NSSC23K0309)
Observing Earth from Above
JOSHUA B. FISHER & GREGORY R. GOLDSMITH
CHAPMAN UNIVERSITY