Developed by the National Oceanic and Atmospheric Administration (NOAA) and its partners, including the University of Maryland, The Evaporative Stress Index (ESI) provides drought warnings several weeks ahead of most other currently available drought indicators. By detecting the advance signals of plant stress, including dry soils, decreased plant transpiration and warming land temperature, ESI can raise the alarm before plants visibly dry out and lose their green appearance.
This new drought index (ESI) – part of NOAA’s GOES Evapotranspiration and Drought Product System (GET-D) – integrates satellite observations of land surface temperatures from NOAA’s Geostationary Operational Environmental Satellite (GOES) with vegetation information from the NOAA/NASA Visible Infrared Imaging Radiometer Suite (VIIRS). Researchers then use these observations to estimate water loss due to evaporation from the soil surface, as well as water that evaporates, or transpires, from the leaves of plants.
“When vegetation is already turning brown, it’s too late. ESI is able to see the onset of vegetation stress before it gets to this state,” said Christopher Hain, an assistant research scientist at UMD’s Earth System Science Interdisciplinary Center (ESSIC) who played a key role in transitioning ESI from the research phase to NOAA operations. “There are other tools that estimate the potential for drought stress by measuring rainfall, wind speed, heat or other parameters. But ESI directly measures the actual stress on plants.”
The new product represents many years of research and support by NOAA, NASA, the University of Maryland, the U.S. Department of Agriculture, the University of Wisconsin, and the National Drought Mitigation Center.
The U.S. Department of Agriculture (USDA) began developing ESI in the late 1990s under the direction of Martha Anderson, a research scientist at USDA’s Agricultural Research Service. Hain began collaborating with Anderson’s team in 2008 as part of his doctoral research at the University of Alabama in Huntsville. From the start, Hain’s main task was to help integrate ESI into NOAA’s research program, with the eventual goal of transitioning the tool from research to operations. Hain continued in this role when he joined ESSIC and the Cooperative Institute for Climate and Satellites-Maryland (CICS-MD) in 2010, with help from ESSIC/CICS-MD postdoctoral researcher Li Fang and former faculty research assistant Zhengpeng Li.
NASA contributed funds for the research phase, and after ESI showed promise as a useful tool for decision-makers, NOAA stepped in to continue building out ESI as an operational product, with UMD/ESSIC managing the development of the system and serving as a central point of collaboration for NOAA, NASA, USDA and end user partners.
“The University of Maryland was responsible for building this system out and transitioning it to operations at NOAA,” Hain said. “When scientists develop a new tool from a research project, there is no guarantee that it will always be available unless it has operational support. And during the research phase, much effort focuses on hindcasting to determine how well the product’s predictions matched real observations. Even the best tool is not useful until it is operationally available to help make useful predictions for the end user.”
Transitioning from a research project to NOAA operations provides end users with a robust support environment so that farmers, ranchers and other stakeholders have access to timely and reliable data, Hain explained.
“As a researcher, your work is only as good as someone else’s ability to use it. So for any effort like this, operational use is the ideal end goal,” Hain added. “Getting to this point with ESI is a testimony to its need in the drought community. NOAA essentially decided ESI is a useful product that was worth making available to the community.”
The GET-D system’s early warning potential shows great promise for rapid onset droughts, also called flash droughts. Flash droughts reach their peak intensity within weeks and usually occur during the growing season, whereas typical droughts can take months or even years to develop. Their quick onset makes flash droughts particularly devastating to farmers and ranchers who have less time to respond to the damaging conditions.
During the devastating 2012 Central Great Plains flash drought, ESI developers observed, for the first time, a rapid change in the ESI in real time. Although ESI was still in the research phase at this time, the observations served as strong evidence that ESI could provide valuable early warning to farmers, ranchers and water managers. The ESI outperformed other indicators by several weeks, suggesting moderate to severe drought conditions well before the U.S. Drought Monitor, for example.
“Droughts are one of the most common and devastating natural disasters, affecting communities across our nation,” said Mark Svoboda, co-founder of the U.S. Drought Monitor. “This new product will help communities spot and prepare for flash droughts, which come on quickly and take a heavy toll on businesses and the public.”
The team of scientists involved in developing the ESI emphasizes that this new product is just a first foundational step toward a global drought monitoring product. With several large global end-users requesting information, researchers hope to eventually expand the ESI to cover the entire world.
ESI development was funded in part by the NASA Applied Sciences Program, as well as the NOAA Modeling, Analysis, Predictions, and Projections and Societal Applications Research Programs.