ARS Celebrates World Water Day: GRAPEX Evapotranspiration Project - Keeping an Eye on Water Use

Bill Kustas, ARS Hydrologist, Hydrology and Remote Sensing Laboratory (Beltsville, MD)

Dr. Bill Kustas is a hydrologist at the ARS Hydrology and Remote Sensing Laboratory in Beltsville, Maryland. He is currently working on the GRAPEX evapotranspiration project which uses high resolution satellite imagery of fields in order to gain information on water usage in California vineyards. Besides being used as a drought index over North America, this technology has been used in Brazil, the Czech Republic, Beirut, Spain, South Korean, and Canada. Using this system to monitor water use for agriculture services over a variety of different landscapes has allowed for their tools to be refined and developed, while also having the benefit of collaborating with foreign scientists who offer diverse knowledge and opinions on water conservation.

What is the objective of your project?

“The proposed project will refine and apply a multi-scale remote sensing toolkit for mapping crop water use and crop stress for improved irrigation scheduling and water management in vineyards in the Central Valley of California, a region of endemic periodic drought. While this work will focus primarily on vineyards, the improved tools will also have applications to fruit and nut orchards and other crops with highly-structured canopies. In California, grapes represent nearly 1 million acres of production valued at approximately $6 billion, while fruit and nut orchards represent an additional 2.6 million acres with crops valued in excess of $10 billion. To sustainably continue irrigated agriculture production in this region, better tools for managing water use are needed.”

Can you tell us about your research project and the international collaboration involved?

“Development of ET tools has been the focus of the ongoing GRAPEX (Grape Remote sensing Atmospheric Profile and Evapotranspiration eXperiment) project, led by USDA-ARS and university investigators and supported logistically by Ernest & Julio Gallo Wineries. During the 2013 to the 2017 growing seasons, micrometeorogical, biophysical and remote sensing data have been collected in adjacent pinot noir vineyards at different levels of maturity near Lodi, CA, with expansion in 2017 to vineyards near Modesto and Cloverdale CA. This significantly expanded the north-south climate gradient as well included different vine varieties and trellis designs for evaluating the ET modeling system. The aim of GRAPEX is to combine in-situ and remotely-sensed data to investigate the effects of canopy structure and row orientation on energy and moisture exchange processes within and above the vine canopy. These findings have been used to enhance our multi-scale modeling system to accurately determine ET from such highly structured canopies, while separating vine water use from evaporation from the inter-row cover crop. A critical component of GRAPEX has been to work closely and collaboratively with scientists at Gallo to ensure that both the experimental data being collected and the models and tools being developed can address critical operational needs. There is international collaboration on this project which includes researchers from Spain and Israel interested in applying the models and tools being developed in this project to vineyards in their countries.”

How has your work with international partners benefitted your project? What skills/expertise/other contributions have they brought to this research?

“Our international partners have contributed significantly to the analysis and interpretation of the experimental data as well as being involved in refining ET model formulations for the unique canopy architecture of vineyards and in the future, orchards. Their skill/expertise in micrometeorological field measurements and analysis and in developing computer code and software for implementing the models/tools in Python have been essential in refining the modeling system for these land cover types making the models accessible to many other researchers not directly associated in the project for evaluation.”

What are some of the critical research areas that still need to be addressed?

“A critical research area is how best to implement the output from the ET toolkit into irrigation scheduling/water management decision support systems. It is important to continue validation of the ET toolkit over different vine varieties and trellis designs as well as expanding to orchards and other high-value crops. The modeling system needs to be tested in other countries and regions for evaluating its robustness.”

Since we’re commemorating World Water Day, our audience will be thinking about the importance of water conservation and the theme of “nature for water” – using natural solutions to overcome water challenges in the 21st century. What is one thing you would like everyone to remember about this topic?

“Fresh water is a limited resource and essential not only for growing crops but life itself. With a growing world population, there will be an ever-increasing demand for food and fiber, which puts a greater demand on water resources for agricultural production while also having to provide adequate water for municipalities, industry, and the environment.”