Future terrestrial biosphere changes are critically dependent on water availability and temperature. The response to water and heat stress can be quantified by measuring the surface evapotranspiration (ET), the key climate variable linking the water, carbon, and energy cycles. ET describes the net exchange of water vapor between the land surface and the atmosphere, and is comprised of water evaporated directly from the soil or other surfaces and water transpired (i.e., used) by plants. Plants regulate water loss (transpiration) by closing the pores on their leaves; however, this response is at the expense of shutting off carbon dioxide uptake for photosynthesis and risking carbon starvation. The process of transpiration also acts to regulate temperature, performing the same cooling function as sweat; if plants cannot adequately cool themselves, they risk overheating and mortality due to heat stress.
How plants respond to changes in water availability can be expressed in terms of Water Use Efficiency (WUE), defined as the amount of carbon fixed per unit water used. Some plants have high WUE and can fix a large amount of carbon using a small amount of water; other plants are less efficient. Low WUE plants risk replacement with increasing droughts, but models disagree on WUE with changes in climate. Agricultural systems are also vulnerable to changes in water availability, with recent mega-droughts devastating US crops in the Midwest for the past two years, highlighting the need to optimize water use and understand how plants use water, especially over the diurnal cycle.
The ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS) will address critical questions on plant–water dynamics and future ecosystem changes with climate through an optimal combination of thermal infrared (TIR) measurements over the diurnal cycle for a wide range of biomes with high spatiotemporal resolution from the International Space Station. ECOSTRESS will fill a key gap in our observing capability, advance core NASA and societal objectives, and allow us to address the following science objectives:
- Identify critical thresholds of water use and water stress in key climate sensitive biomes;
- Detect the timing, location, and predictive factors leading to plant water uptake decline and/or cessation over the diurnal cycle; and,
- Measure agricultural water consumptive use over the contiguous United States (CONUS) at spatiotemporal scales applicable to improve drought estimation accuracy.
The ECOSTRESS mission will acquire data for 1 year, measuring TIR, ET, WUE and the Evaporative Stress Index drought indicator for selected regions of the globe and the entire CONUS.
Principal Investigator: Simon Hook (JPL)
Project Manager: Thomas Glavich (JPL)
Mission Manager: Diane Hope (LaRC)