As the West continues to deal with ongoing drought, many water users are trying to figure out how to use less water. Water managers are also working to better gauge how much water is actually being used.
New research — and satellites — may be able to help, especially as it relates to groundwater. Scientists from the Desert Research Institute used a platform called OpenET to monitor water use at agricultural fields in Nevada and Oregon.
Thomas Ott, a research hydrologist at the Desert Research Institute, joined The Show to talk about what they found and what researchers were trying to figure out.
Conversation highlights
THOMAS OTT: Yeah. So the goal of the study was to really assess OpenET ability to estimate field scale water use. So like how much water is a farmer using in a field to grow a certain crop?
And this would be important especially for those farms that are using groundwater, right?
OTT: Yes, especially so — and any kind of water as well. There are many farms that use surface water, ground water or a combination of the two. So understanding how much water is being used, especially if there's not really any meter or any recording of on the farmer side of what's being used, it's really important to be able to assess that.
So how exactly does OpenET work?
OTT: Yeah. So OpenET ... ET stands evapotranspiration, right? That is the water use. That is a combination from two sources. So one source is evaporation. So think of a lake or wet soil that evaporates water into the atmosphere, you know, from the Earth's surface. The other component is transpiration. So that's water used through a plant. So soaked up through the roots and out through the leaves. So we combine this into evapotranspiration. The open part is the availability of the data. So the idea is to have this estimates of evapotranspiration open to the public and easily accessible by not only water managers but also like individual farmers as well.
So how exactly then are you able to use this data to determine how much water a particular farm or particular field is using?
OTT: Yeah, that's a good question. So it's not exactly a 1-to-1. So the amount of evapotranspiration that comes off the the surface ... that we're estimating from the satellite is kind of a proxy for how much water was applied by irrigation. It's not always 1-to-1, and that was kind of the intention of the study to see how that difference occurred. So this kind of comes into the play of efficiency, right? So how much water applied is actually used by the crop?
In this case, the way OpenET does this is it runs six models. ... It uses a couple different sources of data. The main source is land surface temperature from the satellite. So think of an irrigated or watered grass, right? If you're walking on the grass when it's wet, it feels a lot cooler than it does if you were walking either on dirt or asphalt. That's because of a lot of that energy is going to evaporating that water, and it cools the surface. And we can see that from the satellites that these cooler surfaces are using more water.
Is the calculation that if there is more evapotranspiration, that might mean that there was more groundwater, more other kinds of water used in that field to begin with?
OTT: Yes, exactly. It's pretty much directly correlated. So more evapotranspiration indicates more irrigated water.
Are you able to use this kind of data to measure groundwater in general or does it have to be only groundwater that is pumped to the surface and used for something?
OTT: Yeah. So you can really only see the water that's being used by the plant, right? In terms of OpenET. So the water that goes back into the soil and percolates back down to the groundwater ... We don't see that or water that's run off into a stream or something. We don't see that.
Are there implications for being able to measure groundwater use or at least approximate the amount of groundwater used in a particular area?
OTT: Yeah, very much so. So, it kind of depends on what's going on at the surface, right? Because we can't really distinguish if it's surface water or groundwater looking at open OpenET. We can only say something about how much water was evaporated ... off the surface — or I should say evapotranspired.
So there's additional information that's needed in order to understand if that water was sourced from groundwater or if it was sourced from surface water. In the case of Diamond Valley in Nevada, which is where the study was done, we had pretty high confidence. Well, actually, we knew most of those fields were groundwater only. There were only a few surface water fields that we knew of and we knew where those were. So we were able to account for that.
