BIG DATA Preparing for the future
Data collection and comparison is important for growers as irrigation regulations continue, says Aaron Fukuda, general manager of the Tulare Irrigation District, Tulare, California. As a conjunctive use irrigation district, it relies heavily on surface water not only for irrigation demand but groundwater recharge. The groundwater sustainability agency covers about 100,000 acres in total, with about 70,000 acres of irrigated agriculture.
“We’re currently seeing the impacts of the latest round of drought,” says Fukuda. “Our groundwater levels are actually at an all-time low now. Our boards were very nervous about what was going to happen this year.”
Instead of trying to put off dealing with inevitable irrigation restrictions, the group began implementing water use reduction ahead of schedule to help manage the transition, he says. “In order to do that, we needed a metric to measure how much groundwater we were using.”
Collecting evapotranspiration data provided a baseline for understanding the amount of water actually being used, including how much was being released to the atmosphere compared to how much was being returned to the water table. The most important part was comparing that data against ground truthing methods to calibrate the satellite imagery.
“It’s illuminated growers’ understanding of how much water they were using,” Fukuda says.
Tracking that data over time in a dashboard provides opportunities to see how different irrigation practices and weather events impact the overall water usage. That gives growers the ability to use those models to modify irrigation behaviors to maintain yield within limits and make better decisions to protect profits.
Think of irrigation allocation like maintaining a running bank account with a deposit made at the beginning of the season. Monthly reports can help make smart use of the remaining amount.
Compare for accuracy
From Kimmelshue’s perspective, digital collection of evapotranspiration rates via satellite imagery is one step of the process. While those numbers are determined and then compared to high-resolution imagery, his crew also physically drives through much of the irrigated ag land in the state to create a digital footprint and do ground truthing to see how accurate the ET models are. That cross-referenced monitoring data helps determine how much water is actually evapotranspiring into the atmosphere as opposed to what’s going back into the ground. A groundwater sustainability agency will use those numbers in an allocation formula to find the right amount of water for the crop.
“Many of these GSAs have what they call a glide path,” says Kimmelshue. At first, the grower will be able to pump what was pumped in the previous year. Then, the next year will be an amount that’s a little bit reduced, with an end aim over a multiyear timeframe to reach a sustainable irrigation level. “You’ve got to figure out what you’re going to do over the next 20 years through
Growers should start with sources for reference evapotranspiration crop coefficients and guidelines for irrigation scheduling.
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