Satellites reveal secrets to water-guzzling California farms
Click to enlarge the image and toggle caption Dan Charles/NPR Dan Charles/NPR
State regulators have turned to satellites as a way to prevent further destruction of California's shrinking water resources.
California farmers were able to pump as much water as they wanted from wells in the past. The underground water table has been lowered by hundreds of feet as a result of this unrestricted usage. Now, the state is trying to stabilize these aquifers.
California's agricultural land is vast and California regulators need to know how much water each farmer uses. Scientists and private companies have developed a method that makes use of images from orbiting satellites. Joel Kimmelshue is co-founder of Land IQ and says that agricultural anonymity has ended.
California's 2014 law to protect its aquifers gave water surveillance a boost. It limits the amount of water farmers can pump.
The problem was that Eric Limas, a local official, wasn't clear on how to enforce water usage limits. Limas is the general manager for the Lower Tule River Irrigation Districts and Pixley Irrigation districts, both in Tulare County. These areas have some of the state's most depleted aquifers. Limas is also responsible for the establishment of groundwater sustainability agencies in that region.
Limas states that this was one of the first conversations our groundwater committee had. "Ok, but how will we do that?" Is it possible to measure every molecule that has been pumped?
Limas does not know the exact number of wells in his county. Many of them are hidden in the middle corn fields or almond orchards.
Many farmers were reluctant to assist him. In the first few years following the passing of the law, this was especially true. Limas recalls his initial reaction. "It was like, 'You're crazy' if you think that you're going on my place and .... figure how much I'm pumping. That's my water.
Limas then learned that scientists at California Polytechnic State University had created a method to estimate how much water crops use from images taken by NASA-operated satellites miles above.
Land IQ was using the same technique, but with additional stations on ground to collect data about field-by-field water usage. Limas recalls that it sounded like Star Wars stuff. It was cheaper and easier than installing water meters at every well in his neighborhood.
There are several steps involved in this technique. First, you need to determine which crops are currently growing in each field. Satellite images are updated nearly every week and contain clues such as the shade of green, spacing of vegetation, and the year that the field turns green. Kimmelshue claims that these clues can be combined to create a crop fingerprint. We have a fingerprint to identify walnuts and one for tomatoes and alfalfa.
Kimmelshue estimates that about four percent of cases are due to mistaken identity. He says that it is possible to mistake almonds for peaches. "But almond trees and peach trees have similar water requirements," he says. The estimate of water consumption is still quite accurate.
Click to enlarge the caption Land IQ Lands IQ
Each crop absorbs a certain amount of water at a specific point in its life cycle and releases it through its leaves depending on the local weather conditions. Land IQ has installed monitoring stations at hundreds of locations to monitor wind speed, heat and humidity. Putting it all together, the company calculates the amount of "evapotranspiration," the amount of water that the plants are releasing to the air, as well as what's evaporating from the soil.
This is different than the amount farmers pump because some of the irrigation water pumped from the ground sinks back into it. Kimmelshue convinced Limas officials that it is more important to regulate water use, through evapotranspiration rather than water pumping. Some of the pumped water eventually returns into the aquifer.
Now, he's selling the data to more than 12 groundwater regulatory agencies including Eric Limas.
Limas and his associates can track how much water each farmer uses, field by field. They can also show farmers how this compares with their legal allotment under Groundwater Sustainability Management Act (SGMA). Limas states that many men are looking at their water budgets, and saying "Oh, yeah, we don’t have enough water for that summer crop."
This is how the process should work. To conserve water from the aquifer, farming practices should change. Officials worry that the process won't be as smooth when groundwater usage limits are tightened over the next 20 years. Many are anticipating court battles over the accuracy of the satellite-based method. Farmers fear that regulators may eventually shift to using data from water meters installed at every well.
The technique is becoming more popular in the meantime. A coalition of scientists, NASA and environmental groups such as the Environmental Defense Fund will launch a new version space-based water monitoring next week. OpenET is the name of this new version. OpenET is an acronym for evapotranspiration. It estimates water use in agricultural areas throughout the west United States and makes it accessible online for everyone to see.
