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🔬 "Estimation of Evapotranspiration"


Photo by dan carlson / Unsplash

Table of Contents

Host: Travis Loop
Guests: Robyn Grimm | Director of Climate Resilient Water Information Systems | Environmental Defense Fund &
Forrest Melton | Research Scientist | California State University Monterey Bay
Category: 🔬 Research

Podcast’s Essential Bites:

[2:33] RG: “Evapotranspiration (ET) is the process by which water evaporates from the land surface and transpires from plants. It's the second largest component of the water cycle, and so can be thought of as the opposite of precipitation. It's water that leaves the land surface and goes back out into the atmosphere. And as such, it's a measure of the water that can no longer be used in the local system, after having been applied to the landscape. Some water that's applied may recharge the groundwater basin or runoff into a local stream. But that water can often be used again. ET is the water that's been consumed and cannot be reused. In the West, we tend to pay really close attention to precipitation, water and snow, so the largest component of the water cycle, to get a sense of how much water is available. It's equally important to pay attention to how much water is being consumed, which we can measure through evapotranspiration.”

[3:28] RG: “We like to say that managing water without an understanding of ET is kind of like trying to manage a household budget without really understanding how much money has been spent day to day. Despite its importance though only a small minority of farmers across the West have been able to use this data, in part because it's been so difficult and expensive to get in the past. And similarly, small water managers have also been unable to access this data. And water management really is truly a local undertaking. So being able to level the playing field in the way OpenET does is really critical. The fact that we're making this data widely accessible to both farmers and water managers alike, big and small, we think is a really important piece in meeting some of the water management challenges we're facing today.”

[4:36] RG: “As climate change and drought are putting more and more pressure on our water supplies, we really do need to have a solid understanding of how much water is being consumed by crops and other vegetation as they grow across the landscapes of the West. And as a starting point, this just helps us get a better understanding and ability to track a water budget and a more realistic way and closer to real time. But more specifically, in terms of different end users for this data, OpenET can help rural communities design locally driven water conservation and training programs that use this data as the baseline accounting data for those types of programs. And at larger scales that can help policymakers more accurately track supply […] and simplify regulatory compliance. And the fact that the data is available to both those policymakers and local communities at the same time, we think is really critical in terms of those entities working together and sort of co-developing solutions with a common baseline understanding of what's happening on the ground. And then last, but not least, OpenET can help farmers improve irrigation practices that help them maximize […] crop and reduce costs for fertilizer, water and energy.”

[6:17] FM: “There have been a couple of different techniques that have been available [to track and measure evapotranspiration]. Folks have used something called a crop coefficient approach, where you take […] weather information to calculate what's called reference ET […]. You can think of this as how much water would be used […] by your front lawn […] and then that's scaled by what's called a crop coefficient for individual crop types, locations. These techniques tend to assume that everything is well watered and perfectly growing all the time. And so that can be challenging. Information has also been available from satellite based approaches for measuring evapotranspiration. But it tends to be fragmented produced, using different approaches, and only available for specific regions or specific water managers or water users. One of the things that OpenET is doing is bringing those different approaches together on a single platform to make it easier to compare and understand similarities and differences, identify the strengths of different approaches, and then produce a single estimate that represents a consensus number for evapotranspiration, leveraging the strengths of these different approaches.”

[25:51] FM: “California Delta landowners will soon be able to use OpenET to track their water use, which they're now required to report to the state. And for this use case, OpenET is valuable for two reasons. One, it provides that single ensemble ET value, helping bypass the whole challenge of deciding which model to use. Second, it represents a pretty significant cost savings for these landowners relative to other methods of compliance which are going to require metering of both every point of diversion and every point of return flow in the delta, which is very complicated hydrologically. So OpenET simplifies the regulatory compliance process for them. At the same time OpenET is being used as a rebuttable estimate.”

Rating: 💧💧💧💧

🎙️ Full Episode: Apple | Spotify
🕰️ 37 min | 🗓️ 10/26/2021
✅ Time saved: 35 min