MEASURING WATER SOURCES
Ideally, snow falls and accumulates in mountain ranges over the winter and spring seasons. Snow serves as a water bank, storing and gradually releasing water into rivers and streams in warmer weather. Realistically, warmer temperatures and drier conditions are becoming common trends in winter.
Come springtime, below-average precipitation levels and exceptionally little snowpack quickly evaporate or snowmelt is quickly absorbed by parched soil. Little if any water remains to fill reservoirs or other water storage infrastructure. Changing winter precipitation patterns are another threat to water supply.
NASA research is closely observing central California water sources, their changes over time and causes, in an effort to report information and identify more effective resource management. Satellites, airborne and field missions are recording data on snowfall, rainfall, soil moisture, groundwater depletion, crop health and evapotranspiration.
The Global Precipitation Measurement (GPM) mission tracks rain and snowfall. Analyzing the quantity of water entering and leaving the system will help determine the amount of water that is accessible as well as consumed by agricultural use.
GRACE-FO global observations of month-to-month surface mass changes, 16 June 2021 release from NASA JPL.
Groundwater is especially important in places that don't get little rain and frequently face drought. It is the largest unfrozen freshwater source in the world. Especially in the absence of surface water, groundwater is assumed to be available.
Matt Rodell, Associate Deputy Director of Earth Sciences for Hydrosphere, Biosphere, and Geophysics at NASA's Goddard Space Flight Center studies worldwide groundwater datasets, using data from the agency’s Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission. Unlike snowpack and lakes, the researcher said that groundwater is "stored up over many years, decades, centuries or millennia... You always want to have that water set aside, so it's there for hard times."
California is a global hotspot, one of many areas where groundwater depletion is occurring faster than groundwater recharge. Like savings accounts, groundwater aquifers have been overdrafted. In some areas, even the land has been literally declining or caving in for decades.
MEASURING SOIL MOISTURE & EVAPOTRANSPIRATION
NASA missions like Soil Moisture Active Passive (SMAP) and Moderate Resolution Imaging Spectroradiometer (MODIS) also measure soil moisture and evapotranspiration, respectively. The Landsat program, a joint effort of NASA and the U.S. Geological Survey (USGS), has been measuring crop health and growth for about 50 years.
In partnership with Forrest Melton of NASA's Applied Sciences program, Lee Johnson, Alberto Guzman and Will Carrara of NASA's Ames Research Center support the Satellite Irrigation Management Support (SIMS) system. The online data platform uses publicly available Earth satellite data and open-source models to map evapotranspiration at the quarter-acre scale.
"Evapotranspiration is a really big part of the hydrologic cycle and yet, in the past, a lot of information on it has been difficult or expensive to get," Johnson said. "Everyone knows about precipitation; it's on the home screen of your phone. But evapotranspiration … information has been scarce… for growers who want to use it to guide crop production. And if you can't reliably measure it, it's harder to manage it."
SMAP standard deviation of the difference between global near real-time monitoring of soil moisture and ECMWF model values for ASCAT soil moisture, released from NASA JPL.
Melton explained, "For most crops, evapotranspiration represents the minimum amount of water that has to be replaced through irrigation or precipitation to maintain a healthy crop and maximize crop yields.”
Another water management tool, Grape Remote-sensing Atmospheric Profile and Evapotranspiration eXperiment GRAPEX) uses Landsat data to help vineyard owners and managers. Thermal and visual Landsat images provide information about evapotranspiration and plant health to avoid wet or dry extremes.
“The goal of our work is to find ways to … take petabytes of (NASA) satellite data and turn it into information that can be used for day-to-day decision making,” said Guzman, a senior software engineer at NASA Ames.