IndyMike

Hello Mike, The table below is based on readings from the KBAB weather site at Beale AFB. It shows what the ISY should be calculating for the PM and HS ETo. The HS method is extremely simple. It relies on Min/Max temperature alone. The only way that I can see that you could be getting an ETo of zero would be if WeatherBug was misreporting the Min or Max temperature. if Max - Min goes to zero, your ETo also goes to zero. I simulated a "mis-reported" low temperature in the second table. This produces an varying error in the PM calculation. The HS calculation goes to zero. Could you check the ISY irrigation display and see if high and low temps are being displayed properly? IM

Hello Tim, I believe I understand what you are trying to accomplish. I don't see anything "wrong" with the implementation - it's rather resourceful. Unfortunately, I'm not sure how useful your added programing will be. Based on the KBAB data so far this year, you would have triggered your program a maximum of 2 times so far. The last time you had rainfall > than .38" was on April 4th (0.47 inches). You are now headed into your dry season. Based on 2012 data, you're unlikely to trigger this program until October. Seems like a lot of work... Hopefully Michel's announcement regarding the Weatherbug servers will improve reliability to the point where your workaround won't be required.

Hello dpark, The calculation times have not changed in recent versions. Irrigation Required is still calculated at midnight. If you are currently seeing Irrigation Required as 0.38, it should have been the same value at 5:00 AM. Would you mind posting your program? It's possible that another condition prevented it from running. IM

jmed, You should be using the "interior plains" setting for your area. This yields ETo values nearly identical to those predicted for your regional airport. I downloaded data and CRONOS predictions for your Airport. The following is a comparison for the past month. The data is actually for 90 days, even though I'm only showing a month. 1) ETo comparison: The ISY and the NCSU CRONOS system agree within 0.0315" over 90 days. The equates to 0.00035" difference per day. 2) ETc comparison: The ISY is using a Kc of 0.6 for warm season grass. The NCSU CRONOS system is using a Kc of 0.8 for the same grass. I don't know why. All of the literature that I can find indicates that a Kc of 0.6 is correct for warm season grass.

Jmed, I downloaded data from one of your local WeatherUnderground sites for the past month (below). I ran the P-M calculation on this data and produced the values in the table below. I used the following resource to look up predicted ETo for states in your area: http://www.nc-climate.ncsu.edu/ETdynamic2.php?date=2013-05-27&unit=inches. One of the locations listed is your regional airport. ETo values from that station appear to track the ISY calculation within 0.01". Not sure what to tell you about last years values. Your current values are tracking the NCSU predictions for your location.

Jmed999, A little criticism - all that I can tell from your post is YOU DON"T LIVE NEXT DOOR TO ME! My ET is running 0.07 for the past few days (overcast). I'm more than willing to help, but you have to toss me a bone. 1) location 2) Crop coefficient (Kc setting) 3) Calculation method (P-M or S-H) Feel free to PM me if you don't wish to post on the forum.

Hello dpark, Executing the "Irrigation Complete" command will prompt the ISY to deduct the amount of water you are applying from "Irrigation Requirement". Since you are using "Irrigation Requirement" to trigger your program, the condition is likely turning false, causing the program to exit. Try eliminating any delay statements between the "Irrigation Complete" command and the Email command (may work) or Move the notification prior to the "Irrigation Complete" command.

Hello Pete, I pulled down your weather statistics from 5/11. Based on this data, the ISY calculations are shown below. With a Kc of 0.6 (warm season grass), I'm calculating a ETc of 0.1637 in/day. This is very close to your value of 0.1575 (-0.0062 inches). I also looked at your local Arizona METEOROLOGICAL site "Mohave 2" which appears to be near you. They predicted a ETo of 0.28 inches/day which compares very well with the ISY calculated 0.2729 inches/day (0.0071 inches). The differences here could easily be attributed to differences in local temperatures and windspeed. The Arizona Mohave #2 site is located here : http://ag.arizona.edu/azmet/28.htm. Use the "monthly data" tab to see predicted ETo. From what I can see, your current values should be correct for "warm season grass" using a Kc of 0.6. You mentioned that you also have Palms that you are irrigating. I know absolutely "beans" about Palms and can't advise you on how to adjust Kc to account for them. The current ISY implementation does not account for multiple species of plants or multiple zones. If you determine that the requirements of your Palms are significantly different than your grass, I would encourage you to use a Kc of 1.0 (true ETo) and handle the irrigation requirements for grass/Palms separately via programs.

Hello Mark, My personal experience is that dropouts (Weatherbug no-response) occur more frequently when the polling interval is decreased. I use a minimum polling interval of 5 minutes in my area. I've recently backed off to a 20 minute poll with no obvious impact on the Penman-Monteith calculation. The ISY implementation of the Penman-Monteith calculation uses averages of Temperature, Depoint, and Windspeed. The temperature and depoint inputs are rather slow moving. The Windspeed is fast moving, but weatherbug provides averages (between samples) to the ISY. The ISY calculates averages by dividing a total by the number of samples acquires ( Total Temperature/#samples = average_temp). In a perfect world, the samples would be evenly spaced (5 minute intervals) so that the calculation provides a correct average. Dropouts will affect the spacing of the samples, and thereby skew the average. Normally, this is not significant since the variables move slowly. A significant dropout (hour(s)) will affect the average. The effects on the calculation will be totally dependent on the duration of the dropout and the time of day (can't quantify). The Hargreaves-Samani calculation is sample rate insensitive. In theory, you could acquire 2 samples (11:59 PM and 12:01 AM) and provide all the information necessary. It is used worldwide in locations where reliable Windspeed and dewpoint data are not available. The calculation is NOT as accurate as the P-M. It will significantly underestimate ETo in dry/hot/windy areas and overestimate in humid/cool areas (like mine). I would be very interested in your observations of the new implementation(s). PM me with your location, and I may be able to provide some local state/federal resources that you can use for a comparison. IM

So warm season and cool season grasses Kc are both 0.8? Thanks for the instructions!!! jmed999, Good catch! I had a typo in the warm season grass Kc. This should be Kc = 0.6. I've corrected it in the post above.

pyroman175 and jmed999, Michel had requested a updated Wiki some time back - I'm delinquent. Work has again intruded. In lieu of a good Wiki description, here are the basics: Calculation Method Penman-Monteith: Accurate, but relies on averages of Temperature, Wind speed, and Dewpoint throughout the day. Some users had reported problems with communication to the Weatherbug servers which can cause errors in the averages. Hargreaves-Samani: Less accurate, but relies on Min/Max temperatures alone. These can be acquired during one snapshot at the end of the day. As a result, the calculation is far more robust in the presence of Weatherbug access issues. Absorption Factor 80% absorption is recommended for level ground. This is a generally accepted industry % absorption for rainfall. Users with steep slopes can apply lower percentages to compensate for runoff. Absorption is applied to both rainfall and irrigation: 1) Rainfall .5 inches: Effective rain = 0.8 * .5 = .4 inches 2) Irrigation 0.5 inches: Effective irrifation = 0.8 * 0.5 = .4 inches Crop coefficient Plant needs are species dependent and defined as ETc = ETo * Kc (Kc = crop coefficient). Cool season grasses (Bluegrass, Rye, Fescue) use Kc of 0.8 Warm season greasses (Bermuda, Saint Augustine, Zoisya, and Centipede) use a Kc of 0.6. Edit: corrected Kc for warm season grasses. Additional values are provided to encompass a range of plants/trees/gardens. Note: the current Evapotranspiration variable is actually ETc (=ETo * Kc) Pryroman, Wind speed will significantly affect your ETo calculations. If you feel that the updated calculations are different than local predictions, PM me with your location (weatherbug) and I will run some calculations. IM

True, the ISY could calculate average rate if it had a reliable Weatherbug feed (xx readings per hour) to calculate an average. Many sites do not support multiple readings/hour and other factors such as user network issues and Weatherbug server loading make this a questionable calculation. If a rain rate could be determined, we would then be faced with how to apply it. Level clay soil would generate standing water that would eventually be absorbed (80% absorption). Clay soil on a slope would generate runoff (10% absorption). In order to apply the information, we would need a multi-zone setup with information on the soil type(s) and slopes. The above sounds as if I'm making excuses. I have put a fair amount of time into researching different ET system implementations. The commercial systems that try to achieve the level of precision required for rain rate/runoff calculations use dedicated sensors and muti-zone definitions. Neither are currently available to the ISY. Stepping down from the podium... From your example program below - Your ET will not change significantly in the morning hours due to high humidity and no sun. Rather than checking to the 0.5 limit, why not check a range of depletion and simply run at 4am: If irrigation requirement > 0.4 (run) This will help cover your 0.15 ET for the day. For the rain instances, you can use a series of programs to program a state variable: State 0 (rain 0 to .1) if Rain_today> 0 and Raid_today <=0.1 Then Rain_state = 0 State 1 (rain .1 to .2) if Rain_today > 0.1 and Rain_today <=.2 Then Rain_state = 1 Irrigation if irrigation requirement > 0.4 and Rain_State = 0 Then Run irrigation Other comments - 1) Your silt loam is actually a much nicer soil than what I have. Use the charts above to gauge your watering needs (after the sod is established). 2) After the initial 10 days your sod will still have next to no roots (maybe 2"). I have no personal experience with sod. I would listen to your sod installers on how much water/how often to apply. You are installing at a really tough time of year. The 0.5" in your program examples should be excessive given the short roots (but listen to your sod people). 3) I am not a fan of watering in the evening in our areas (I'm 90 miles east of you). Prolonged wet periods in the summer promote nasty diseases. I would rather underwater than water after 6 PM. 4) The chart below shows the monthly average ETo for your area. This includes rainfall/cloudy cool days. Some hot summer days may be significantly higher (2x). Even so, you should not have a problem with odd/even watering once your sod is established.

During a rain event - my ISY shows the rate in Rain_Rate coming from Weatherbug - and manual measurements I am planning to do will give me the inches/hour of my system. Does the ISY not take this into account at all? I would think that it could. Anyway - I'm really not needing/wanting to get into this. Just adjusting the amount applied responding to the climate (ET and rain). Michael. Michael, The manual measurements of your irrigation system are correct. You do want to control the irrigation rate to make sure you aren't getting runoff. The "Rain Rate" provided by Weatherbug is a maximum that does not include a duration. When Weatherbug shows a maximum rate of XX inches/hour, the ISY cannot determine how long the event lasted (seconds, minutes, hours). As a result, the ISY can't determine how much water may be lost to runoff. There are systems that can determine actual rain rates and durations - they use dedicated sensors and are not inexpensive.

Hello Michael, I'm going to apologize up front because I will be ignoring many of your questions - let's cut to the chase: [*:20ddw585]You are installing a new irrigation system and new sod - both are sizable investments. New sod is a great way of obtaining an instant lawn. It's also a water PIG. Personally, I would talk to your sod installers about the irrigation requirements and do EXACTLY what they say. They should understand your local restrictions and the sod requirements. I'm guessing that the watering requirements will be far in excess of anything the ET calculations indicate. Get the SOD to establish itself first, then we can worry about efficiency. [*:20ddw585]Talk with your irrigation installers - you want all of your sprinkler heads "tuned" so the provide a constant rate across the zone (xx inches/hour). [*:20ddw585]After the system is installed, measure the application rate and coverage efficiency using the link I posted to Jmed999. Since you have a new system, I would call the installers if the irrigation rate changes significantly across a given zone (poor overlap/incorrect nozzle sizing). [*:20ddw585]Lastly - the ET numbers that you posted (0.8 and 1.7) are way off for Chicago (actually, there way off for most anywhere). If the units are in inches, you should be seeing around 0.14 inches/day. If the units are millimeters, you should be seeing around 3.56 mm/day. Sorry for ignoring your questions on programming. I would much rather see you get the sod established first, and then worry about efficient watering. IM

Hi jmed999, Answers below - That would be my recommendation. As I stated, you may need to adjust depending on whether you have flat/sloped ground. The irrigation rate is your responsibility. If you have a high irrigation rate (inches/hour) and heavy soil/slopes you will need to apply multiple waterings to prevent runoff. To the best of my knowledge, the "allowable depletion" is presented as a guide. It is not used for programming. I've actually requested that UDI eliminate this in favor of the water balance table above. Glad to hear that. I'd be interested in your system type (spray, rotor, rotator) and your results. IM

-When you say you apply 0.2" of water do you mean your irrigation system applies 0.336" which equates to 0.2"? So you apply 0.336 and only 0.2" is absorbed, right? Seems like if you need 0.336" and allowable depletion = absorption factor you would need to apply 0.56" since 0.56*.6=0.336. If you want to replenish the amount that has depleted (0.336") then wont you need to apply 0.56" since only 0.336" will be absorbed? -Also, for loamy sand (your soil) the ISY has an allowable depletion of 83% which is different from your chart of 60%. Why such a difference? Hello jmed999, I'm running with a Soil Absorption setting of 80%. I tell the ISY that I've applied .25" and it deducts 0.2" (80% * .25 inches) from the irrigation required. On the subject of Soil Absorption - I regard this as a misnomer. In order to calculate soil absorption you need to know the Rain/Irrigation rate (inches/hour). That information isn't available to the ISY. As an example: Heavy clay soil is capable of absorbing around 0.1" of water/hour. 1) If you are on a slope, and received 1" of rain in an hour, only 0.1" will be absorbed. The rest would be lost to runoff. 2) Given the same slope, if you received 1" of rain over the entire day (1/24 = 0.042 inches/hour). Most of the 1" of rain would be absorbed (until you saturate the clay). Instead of using the term "Soil Absorption", I treat this as a "watering efficiency" and set it to 80%: 1) The 80% number is generally accepted as a rainfall efficiency in the irrigation industry. It accounts for runoff and evaporation from the plant canopy (water not reaching the soil). 2) The same 80% is applied to irrigation. An 80% efficiency is at the high end for most irrigation systems, particularly rotor systems that are operated during the day (spray evaporation, wind effects, poor overlap). You can compensate for this by simply running your system longer and telling the ISY that you are applying the same amount of water. Summarizing the above: 1) I would suggest that everyone use a baseline of 80% absorption. People on slopes may need to "tailor" the number downward. People in flat areas may need to "tailor" upward. 2) Please do not use the "allowable depletion" from the ISY. Use the water balance table the I presented previously. The allowable depletion item was based on the "soil absorption" entry - as explained above, this can't be determine with the information the ISY has available. 3) There is no substitute for "measuring" your irrigation rate and coverage (overlap). This is particularly important for Rotor or impulse style heads. Most systems are installed with one size nozzle in all of the heads - this disregards the area covered (45, 180, 360 degrees) and leads to huge differences in the application rate. Section 4 (page 19) of the following provides worksheets and describes how to perform a "catch can test" to determine your irrigation efficiency: http://www.irrisoft.net/downloads/manuals/InSite%20Users%20Guide.pdf

If weatherbug doesn't respond none of the variables are updated - you get the last valid value.

Hello MWareman, We're getting into "irrigation methods" here. This is very dependent on your location, soil structure, (and in your case) watering restrictions. I can offer some suggestions, but you'll really need to test to see what works best in your particular situation. In the example... If Irrigation_Required > 0.5 and Rain_today < 0.5 ..this gets messed up if it effectively rained 0.4" (meaning I'm applying 0.4" too much - and wasting water). If Irrigation_Required > 0.5 and Rain_today < 0.2 ..this gets messed up if it effectively rained 0.3" (meaning I'm getting .2" too little). Because Irrigation_Required is updated only once a day at midnight - what I really need to do is subtract Rain_Today from Irrigation_Required and see if the result of that exceeds my threshold. I cannot seem to do that in an ISY program (in the same way that water applied by irrigation is currently subtracted from the irrigation required when a cycle complete is executed). I also have every-other-day and time-of-day restrictions to my irrigation - so I have to be able to do the math for twice a day irrigation on the days allowed. During the summer months (and factoring the absorption rate) it is very difficult to apply the needed water in only one cycle without busting the time restriction. In the examples that you provided above, I would err on the side of applying too little water (example 2). Grass is pretty tolerant too little water. You can absolutely kill it with too much water (fungus and other diseases). You need to envision your soil as a leaky container (sponge). It you overfill the container you will get runoff and rapid percolation. The soil will rapidly loose water until it achieves it's "Field Capacity". The Field Capacity is determined by the soil type and root dept of your grass. The heavier the soil and deeper the root depth, the more capacity you have. I happen to have loamy sand with a ~8 inch root depth. From the table below: 1) Field capacity = (0.07 inches water/Inch depth) * (8 inch root depth) = 0.56" water 2) Allowable depletion (60%) = (0.6) * (0.56" Field Capacity) = 0.336 When the ISY tells me that the Irrigation Required = 0, it is effectively saying that the soil is at Field Capacity. When it tells me that Irrigation Required = 0.336, I am at the maximum allowable depletion. I apply 0.2" water. Because my soil is light and can't hold much water, I normally need to water daily in the Summer (4:00 AM). I also practice "deficit" irrigation - I allow my water balance to get below 60%. It promotes root growth in the grass. Please perform the calculations for Field Capacity and post back. I have a suspicion that you are trying to apply too much water - don't overfill the container. Under-filling by 0.2 inches isn't a problem. Real time calculation of ET requires a real time measurement of Solar Radiation (Rs). Weather bug does not provide Rs and hence only daily calculations can be performed. Real time updates of Irrigation_Required is left for the user to implement through programs as discussed above. While the ISY could perform this calculation - it would invalidate existing users programs. In other words, this is a question for the UDI team and the forum as a whole. Your watering restrictions do present some unique challenges. I haven't had to deal with them. Please post back the following: 1) Soil type 2) Root Depth 3) Soil Absorption % 4) Current daily ET (estimate) We'll see if there may be an inventive solution. Right now I'm thinking you could use State Variables to guestimate tomorrows ET loss (non-watering day) based on the time of year. IM

Hello MWareman, You are very close on your understanding of the WB module: The ETo, Irrigation Required and, Water deficit numbers are calculated once after Midnight. Rain today is a live number from WB. Water_Deficit = ETo - ((Rain_Today + Irrigation) * Absorption_Factor) Irrigation_Required = Irrigation_Required + Water__Deficit (cannot be less than 0) Note that the Absorption_Factor is applied to both rainfall and irrigation. Add Rain_Today to the qualifiers in your irrigation program: If Irrigation_Required > 0.5 and Rain_today < xx Then Run Irrigation_Program

Hi kaisersoze, Thank you for providing the address for the WB backyard station. This particular station has feeds for both Weatherbug and WeatherUnderground. WeatherUnderground is useful since it provides historical data. The "classic" Penman-Monteith calculation for ETo requires measured Solar Radiation (Rs). Weatherbug does not support Rs data in their API. As a result, the ISY is using an approximation based on elevation, temperature, and location (coastal or inland). The approximation works very well on average. As you've noted, it has a tendency to over estimate on very cloudy days. Fortunately, these are low ETo days and the errors should be on the order of hundreths of an inch. It should perform very well on sunny days - in contrast to your observations. This is my reason for posting. I would have expected your sunny day calculations to perform better than you have indicated. Using the WeatherUnderground interface for your local station, I pulled the historical data for the month of April. The table below shows what I believe the ISY should have calculated on a daily basis. I agree with your cloudy day numbers (4/14 - 4/15) of 0.07 to 0.09 ETo. I do not agree with your sunny day numbers (4/18 - 4/20) of 0.13 to 0.15. Something is wrong here, a Weatherbug sampling error. To assess the calculation accuracy, I pulled CIMIS data for your area. CIMIS provides all the necessary data inputs for the calculation, and maintains historical calculated ETo. The Escondido appeared to be the best match for your location. The following shows the CIMIS data and ISY predicted calculations for the current week. It also shows the ISY calculation error for the week based on the CIMIS "PM ETo" calculation. Remember that CIMIS is using measured Solar Radiation, whereas the ISY is using an approximation. Given Identical input data, it would appear that you should be using a setting of "interior" in your climate settings with a resulting error of 0.058" ETo (4.7% error). Surprisingly, the Hargreaves-Samani equation is performing better still (implementation is in process). I would not expect this to be the case over a longer period of time. So, why are you seeing different values? Possibilities: 1) The ISY P-M calculation relies on averages for Windspeed, Dewpoint, and Temperature. These are averaged over the course of the day. While High/Low temperatures are used, these can be acquired in a single "snapshot" at the end of the day. Communication dropouts will cause errors in the data averages. 2) Weatherbug location changes - If a station is unavailable, weatherbug will automatically switch to a "close" alternative. In some areas, where the terrain changes drastically in short distances, this can be a huge source of error. Disclaimer - I do not know if weatherbug does this for "backyard" locations. 3) Poorly placed/maintained station. Stations used for general weather conditions are often not suitable for ETo calculations. The ETo calculations require proper placement and maintenance of the equipment. Note: this is a general comment - your selected PABLOCO station appears to be reporting data that is consistent with CIMIS. If you have correlated the readings between CIMIS and PABLOCO then this is an excellent choice. My hat's off the the backyard operator. Communication errors are the reason that the UDI team is investigating the Hargreaves-Samani ETh calculation. Since it relies on only the max/min temperatures of the day, the data can be acquired in a single snapshot. Averaging is not required. On the subject of communication errors - when I visited the Wetherbug backyard and WeatherUnderground sites for your local station, I found some interesting differences: 1) Weatherbug was reporting a high temperature of 81.2 degrees recorded at midnight (00:00) 2) WeatherUnderground was reporting a high temperature of 59.4 degrees. This could be a simple website translation error - I don't know what the API is transmitting to the ISY. If the 81.2 degree high is being communicated, there will obviously be some significant errors. Weatherbug has been having issues with the feed from the backyard stations for some time now. Is there another station that you could use? Edit: I was able to connect to your local station using the ISY. It did report a high temperature of 81.2 degrees for the day. Based on the stations reports for the day, and the weather graph presented, 81.2 degrees simply isn't possible. Apparently Weatherbug is still having issues. The Station master for this site provides data to the NWS/NOAA in support of the MESONET. In other words, he/she takes this stuff seriously and probably doesn't realize that the data is being misrepresented on weatherbug. You may want to notify him/her.

Mike, I looked over your XML files. Hard to tell whether the calculations are correct since the data isn't continuous. I did notice that your April 2 data included a 121' elevation. Elevation is reported directly from Weatherbug. This is either a corrupt transmission, or an example of Weatherbug switching stations automatically (really annoys me). If this was a station switch, it was obviously a rather distant station.

I think they're still down. I have 0 stations showing online in all of Michigan/Indiana

Hello Mike, I'm still struggling with your soil system. Comments below - Normal soil structures have been characterized and assigned "Field Capacity" (FC) numbers base on the soils ability to hold water. You stated that you were using a "loamy sand" soil classification and had 6" - 8" of soil. From the table below: 1) 8" of soil @0.07" per inch of root depth (8 x 0.07) = 0.56" in H20 Field Capacity. This is the maximum water that that classification of soil is assumed to be able to hold. 2) Assuming an 8" root depth, your Maximum Allowable Depletion (MAD%) is 60% (0.6*.56" = .34" water depleted). Problems: 1) The table assumes a normal level of percolation - any irrigation above the Field Capacity of 0.56" is assumed to run-off (heavy soil) or be lost to percolation. 2) While a heavy rain in excess of the FC will saturate a "normal" soil, Evapotranspiration will be increased as will percolation. Normally, the FC will be re-established within 24 hours. In other words - the ISY is correct in re-starting irrigation after 48 hours. It is assuming a "normal system" that has re-established the FC due to run-off/percolation. 3) As I stated previously - your lava cap prevents Percolation. This effectively throws the concept of Field Capacity out the window. You effectively have a closed container that can be filled to saturation and is only subject to drainage due to elevation changes. I have not found a "residential" application that can account for the lack of Percolation. The alternative is active soil moisture measurement. As I said in the lead in, I have not come up with a good solution for this. In the meantime: 1) Adjust your soil type to sand (100% absorption). This will help account for the lack of percolation. 2) Historically, your summer months will be marked by lower rainfall and higher ET. This should lesson the problem of Rain storage above the lava cap. 3) Your normal March ETc was 2.4" vs a rainfall of 2.2". Assuming your soil is retaining the rainfall, that's not enough difference to worry about. You might consider disabling the system from Jan through March. That's a news item for me. I did not realize that you had a means of measuring the soil moisture. Could you post back the make/model of your tester and any measurements that you have performs? I rolled up my data this morning. I'm rather disappointed: 1) I forgot about the time zone difference. I believe the ISY was pulling numbers for your site 3 hours early. 2) I had modem issues (1st time in over a year) on 4/3. I missed some rainfall on that date as a result. 3) Sampled the KAUR site at 5 minute intervals. Had 3 errors over the space of 5 days (seems reliable). Other than the loss of data on 4/3 (Modem down), I don't see anything incorrect in the following. Please let me know how I can get your recorded data. PM me if you need an Email address.

Hello Mike, I've been reading Engineering Manuals for the past couple of days. After educating myself a bit more, I am have to retract an earlier statement: The ISY is correct in not allowing a negative water requirement. This is accepted practice in the absence of a detailed site analysis and/or active soil moisture measurements. From the US Dept of Agriculture Engineering Handbook:(FC is Field Capacity) What I view as important in the above is the phase "percolation below the root zone" - You have rock below the root zone. There is no percolation. From your previous description, you have 6 - 8" of topsoil above the Lava cap. Referring to the graphic below, when it rains (or you irrigate) a portion of the water will travel through the soil and hit the lava cap. As you noted above, the slope of your land will cause the water to travel downward until it hits an obstruction (curb, driveway, foundation). The soil near the obstruction will become saturated as a result. As you probably already know, saturated soil is not a healthy environment for grass. Under watering grass will cause it to go dormant. Over watering can kill it (in a much shorter time). I do not have a solution for heavy rainfall. The ISY calculation should accurately calculate the ETo for the upper end of your slopes. If the low end of the slopes are being dammed by an obstruction (saturated), you'll need to apply some "Kentucky Windage". From the looks of your weather history, heavy rainfall should be gone until November. As far as irrigation is concerned, I think you have to correct approach in applying .25" per watering. I would not run the system twice in a day (.5") unless the ISY tells you that you lost over .5" the previous day. Based on your ET#'s, you're not there yet. Most irrigation manuals promote "deep watering" of 0.5" to promote root growth. With only 8" of soil, your grass roots have little room to grow. In other words, daily watering of .25" will cause less drainage to the lower sections of the lawn whereas 0.5" watering every other day may saturate the area. The Rotator heads are nice. I wish they had them when I laid out my system. They are susceptible to wind (which you appear to have a lot of). Be careful watering in the evening when the winds may be high - your uniformity will go to the wind (pun intended). If you are interested, I've used the following site many times over the years as an irrigation reference:http://www.irrigationtutorials.com/reviews/rotor/mprotator.htm I am still interested in the numbers that your ISY is providing. Let's give things a couple more days, then we can compare notes. I have some more suggestions, but want to see the numbers first.

Hello Mike, The station name was a typo. I'm monitoring KAUN. I've updated the charts based on your settings. I have to admit that your soil structure has me a bit mystified. I have no idea what a "lava cap" is. "Highly absorbent" and "runoff" don't normally go together unless you are applying water at a very high rate. From your description, this sounds like soil that is 100% absorbent but quickly hits a saturation limit. I don't know how to model that - yet. Questions: 1) What type sprinkler heads are you using (spray, rotors, etc)? 2) Have you measured the application rate? Observations: 1) If you are able to saturate your soil with the sprinkler system, the same will be happening (probably to a greater extent) when your receiving your 1" of rainfall. 2) The above being the case, retaining the full value of 1" "rain today" is completely incorrect. Most of this would be lost to runoff after the soil becomes saturated. I still do not understand the 7" offset. If I add the total ETo for the month of march (disregarding rain) I get about 3". In other words, your system should never have approached the 7" offset. If this number is correct, something is very wrong. I have my ISY set to monitor your KAUN site using the numbers you posted. If you could collect numbers over the next few days we can compare to see if you are somehow getting corrupted data. The easiest way to pull your data is to use the REST interface via your browser: 192.168.XXX.XXX/rest/climate. Save the XML file and we can compare notes. IM