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Avoid Clamping Flex Moisture Balance at Zero

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#1

In the example below, it seems like it would be better if Flex didn’t clamp the moisture balance at zero if evapotranspiration is going to exceed the irrigation value:

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My understanding is that the zero point is just a semi-arbitrary threshold (driven by AD) that tells us when it’s time to water again. If ET is going to take the moisture balance below zero, then it seems like we could/should water more to make up the deficit. In other words, on Jun 14 I’d expect to water 0.30 inches in order to get back to the zero point. Otherwise, it seems like a series of hot days could continuously drive the “real” moisture level below the AD threshold.

Heat wave and Crop Evap
#2

Hey @ldslaron-

We currently do not continue to track moisture balance once it hits 0%, which is why we cap at zero. We have discussed changing that. One question was if you dipped below that line, would you expect flex to run longer the following run to bring you up to field capacity, or would you expect the duration to remain the same for flex and just not bring you all the way back up?

#3

I could see what @ldslaron is getting at as being a benefit. 2 weeks ago my system went offline and so I flat lined for 2 days.

My system watered for 2 days straight afterwards at it’s normal watering, but technically, since it was at 0 (50% AD for me) for a couple days, my water balance isn’t correct going forward in relation to where it was at before the flat line.

I say this. I don’t want my system watering longer the next day to catch up, since my settings are dialed in for my correct soil and root depth. I don’t need standing water. I would think the easiest bet is to take the negative moisture balance and just add to that and let the system catch up.

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#4

I agree with @Modawg2k. And I can see that I’m going to start experiencing this problem shortly. Last night, AerisPulse predicted quite a bit of rain. Everyone else in Charlotte got it, and heavy. I didn’t get one drop!! And it’s beginning to look like the same thing is going to happen today. So I would really appreciate if it saw it was going below my allowed depletion.

#5

@mckynzee, from my perspective it seems better to be proactive and notice that we anticipate moisture balance will go negative so we can honor AD. So in the example I posted we might water 0.25 inches on June 14 to bring the balance to zero and similarly 0.33 inches on June 15. Otherwise we could get into a situation where the “real” moisture level drops far below the AD (ET > Irrigation persistently), possibly even to the wilting point, yet Rachio will still report it as “0%”. Counterintuitively, if the user tries to mitigate via a smaller AD value (don’t let things dry out as much), things actually get worse.

Granted, runoff is a consideration here as @Modawg2k pointed out but I’m not sure how else to avoid the vicious cycle besides watering more than once per day (really what smart cycle is doing already).

#6

To boil this down, if AW * root depth * AD < Daily ET, we can “flatline” as @Modawg2k puts it.

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#7

It seems there are two problems; one when system is down and flat lines thus causing zero readings and two when flat lines because of actual difference between irrigation and evaporation which can be calculated.
One- the system would have to recognize it was down, for how long and then calculate what it should have watered. If it can recognize it was down, then I would assume it would also be able to calculate the deficiency and send an alert as well as add a % to duration for number of days down.
Two- the depletion is recognized immediately by subtraction and adds frequency to make up the difference.

#8

In my opinion, Rachio should simply track and show the absolute moisture level (zero is zero % moisture), and trigger irrigation when moisture level falls below the allowable depletion level, and irrigate to raise moisture level back to full. The allowable depletion level can be a dotted line on the moisture level graph. For example, root depth=10, AW= .1. 100% = 1 inch of moisture. If allowable depletion is 70%, then irrigation is scheduled when moisture level hits 0.3 inches or 30% moisture remaining. Irrigation brings the moisture level back to 1 inch.

A secondary improvement would be to irrigate to more than 100% if the predicted evaporation is higher than normal. Not sure how to calibrate this feature, though.

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#9

I agree that showing absolute moisture level with a dotted line for AD might be more intuitive. Good idea, @jkb.