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Evapotranspiration Comparisons at Wunderground Gages
along the Lower Colorado River AZ-CA (w/Nexrad Radar Areal Rainfall)
Jun 1, 2011 to May 31, 2012
 

 

Summary of what lies below

% Difference is the error in total rainfall or toal ET, a measure of bias.

MAE % is the mean of the individual daily unsigned differences, a measure of error variablility.

 

ET:

   

CIMIS versus Wunderground... Mano y Mano

  

The California Irrigation Management Information System (CIMIS) is a program in the California Department of Water Resources that manages a network of over 130 automated weather stations in the state of California for the computation of reference Evapotranspiration (ET).  ET is the loss of water to the atmosphere by the combined processes of evaporation (from soil and plant surfaces) and transpiration (from plant tissues). It is an indicator of how much water your crops, lawn, garden, and trees need for healthy growth and productivity.

  

The standard ASCE Penman-Monteith reference ET calculation uses the parameters air temperature, humitity, wind speed, and solar radiation collected at a properly sited automated weather station.  The ideal gage siting would be to centrally locate the station in a large, well-watered turf area that is a considerable distance from objects that might disrupt wind flow or shade the station. The terrain surrounding the weather station should be relatively level if possible.

  

This comparison is to evaluate the difference in a properly sited and maintained CIMIS weather gage calculated ET with solar data to a nearby or not so nearby Wunderground weather gage which is most likely not properly sited or maintained and with out solar data. Real-time Wunderground weather gages are located in thousands of locations around the world that can be used to calculate ET even without solar radiation info at the Wunder Gage.  The automatic retrieval, computation, and storage of ET at both sites are made by my program GetRealtime.exe.  Although CIMIS reports their CIMIS ET it was not used here... err... just because... and ASCE takes a dim view of these renegades. ;-)

 

Properly sited and maintained CIMIS weather station above....

versus

Typical Wunderground site and hard to maintain weather station below.

 

The geographical area selected for comparison are the SUNNY (solar less a factor in regional regressions used by GetRealtime.exe) irrigated Ag districts along the Lower Colorado River in Arizona and California.  Also, ET tends to be a concern to those in sunny areas. Although Arizona also maintains an ET network (AZMET), I have not automated the retrieval of data from their system and so only the CIMIS sites are used here to see how far is far. Hourly CIMIS data are made available every 6 hours while AZMET hourlys are only updated daily.  If you would like to automate retrieval and computation of your own weather data go to my GetRealtime Help page.

 

A real-time Wunderground weather gage was selected in each of the folowing agricultural districts for comparison:

 

1) Imperial Valley, CA (IID)

2) Coachella Valley,CA (CVWD)

3) Palo Verde Valley, CA (PVID)

4) Yuma and Gila Valley, AZ (YCWUA, YID, NGVID)

5) Wellton-Mohawk Valley, AZ (WMID)

6) Parker Valley, AZ (CRIT)

 

Looking at the above photo of a typical Wunderground gage site, one would expect higher temperature and lower humidity would increase calculated reference ET. Windspeed may or may not be higher than the CIMIS 2 meter level. Although Wunderground participants at the selected sites here do not have photos of their gages available, zooming in with Google Earth on the Imperial Airport, Yuma Mesa #2, Wellton-Mohawk, Palo Verde, and Parker Wundergages appear located in open areas adjacent to irrigated areas and should show better comparisons at first glance than those located at residences at Coachella #1 and #2,  and Yuma Valley #1. I think we have a better shot at a good outcome than I thought.  Let's find out.

 

 (Comparing actual temp, humidity, and wind speed would be dullsville and would take all the fun out of this first try.  Hmm... I just realized that both CIMIS and Wunderground have historical data to complete this study in 1 retrieval, but Wunderground stations are here today and gone tomorrow so let's let this drama play out.  And NEXRAD radar rainfall images are only available for the past 4 hours.)

 

 

1) Imperial Valley, CA

 

Wunderground Gage: KIPL, computation time step=hourly, parameters temp, humidity, wind speed, NO SOLAR.

GetRealtime setup file: KIPL; -27508; ET Grass; Imperial Airport Gage, Ca ET; 0; 32.834,-115.579,-120,-54,0.75; P4 (note the wind speed factor of 0.75 to correct airport offical 10 m height to 2 m)

  

CIMIS Gage: 087 Meloland, CA, computation time step=hourly, parameters temp, humidity, wind speed, solar. 

GetRealtime setup file: CIMIS-087; -27538; ET Grass; Meloland, Ca Cimis; 0; 32.81,-115.45,-120,-50,1; P5

The CIMIS gage is located 7.6 miles east of the Wuderground gage.

 

The daily graph comparison below includes in the title MAE, mean absolute error, which is the average of each of the unsigned daily computed ET value difference in percent..

 

 

 

2) Coachella Valley, CA (2 gages)

 

Wunderground Gage #1: KCAINDIO5, computation time step=5 minute, parameters temp, humidity, wind speed, NO SOLAR.

GetRealtime setup file #1: KCAINDIO5; -27506; ET Grass; Indio Gage, Ca ET; 0; 33.739,-116.192,-120,1,0.75; P4

  

CIMIS Gage: 200 Indio II, CA, computation time step=hourly, parameters temp, humidity, wind speed, solar. 

GetRealtime setup file: CIMIS-200; -27536; ET Grass; Indio Ii, Ca Cimis; 0; 33.75,-116.26,-120,40,1; P5

  

Wunderground Gage #2: KCAPALMD17, computation time step=15 minute, parameters temp, humidity, wind speed, NO SOLAR.

 

GetRealtime setup file #2: KCAPALMD17; -27503; ET Grass; Palm Desert Gage, Ca ET; 0; 33.739,-116.311,-120,150,1; P4 

   

The CIMIS gage is located 4.0 miles west of  Wuderground #1 and 3.2 miles east of gage #2.

 

The daily graph comparison below includes in the title MAE, mean absolute error, which is the average of each of the unsigned daily computed ET value difference in percent.

 

 

 

3) Palo Verde Valley, CA

 

Wunderground Gage: MCBRA3, computation time step=15 minute, parameters temp, humidity, wind speed, NO SOLAR.

GetRealtime setup file: MCBRA3; -27509; ET Grass; Cibola Gage, Az ET; 0; 33.304,-114.693,-105,357,0.75; P4

  

CIMIS Gage: 175 Palo Verde II, CA, computation time step=hourly, parameters temp, humidity, wind speed, solar. 

GetRealtime setup file: CIMIS-175; -27539; ET Grass; Palo Verde Ii, Ca Cimis; 0; 33.39,-114.73,-120,230,1; P5

 

The CIMIS gage is located 6.3 miles north of the Wuderground gage.

 

The daily graph comparison below includes in the title MAE, mean absolute error, which is the average of each of the unsigned daily computed ET value difference in percent.

 

 

 

4) Yuma Valley, AZ (2 gages)

 

Wunderground Gage: KAZYUMA11, computation time step=5 minute, parameters temp, humidity, wind speed, NO SOLAR.

KAZYUMA11; -27505; ET Grass; Yuma Valley Gage#1, Az ET; 0; 32.712,-114.666,-105,125,1; P4

  

CIMIS Gage: 186 San Louis, Mexico, computation time step=hourly, parameters temp, humidity, wind speed, solar. 

GetRealtime setup file: CIMIS-186; -27535; ET Grass; San Louis, Mex Cimis; 0; 32.49,-114.83,-120,48,1; P5

 

Wunderground Gage: KAZYUMA16, computation time step=5 minute, parameters temp, humidity, wind speed, NO SOLAR.

KAZYUMA16; -27502; ET Grass; Yuma Valley Gage#2, Az ET; 0; 32.665,-114.633,-105,200,1; P4 

 

The CIMIS gage is located 18.0 miles south of the Wuderground gage #1 and 16.7 south of #2.

 

The daily graph comparison below includes in the title MAE, mean absolute error, which is the average of each of the unsigned daily computed ET value difference in percent..

 

 

 

5) Wellton-Mohawk Valley, AZ

 

Wunderground Gage: KAZWELLT4, computation time step=5 minute, parameters temp, humidity, wind speed, NO SOLAR.

GetRealtime setup file: KAZWELLT4; -27504; ET Grass; Wellton Gage, Az ET; 0; 32.691,-114.044,-105,310,1; P4

  

CIMIS Gage: 201 Andrade, Mexico, computation time step=hourly, parameters temp, humidity, wind speed, solar. 

GetRealtime setup file: CIMIS-201; -27534; ET Grass; San Louis, Mex Cimis; 0; 32.674,-115.044,-120,120,1; P5

The CIMIS gage is located 58.2 miles west of the Wuderground gage.

 

The daily graph comparison below includes in the title MAE, mean absolute error, which is the average of each of the unsigned daily computed ET value difference in percent..

 

 

 

5) Parker Valley, AZ

 

Wunderground Gage: MTS917, computation time step=5 minute, parameters temp, humidity, wind speed, NO SOLAR.

GetRealtime setup file: MTS917; -27507; ET Grass; Parker Gage, Az ET; 0; 34.131,-114.327,-105,357,1; P4

  

CIMIS Gage: 135 Blythe NE, CA, computation time step=hourly, parameters temp, humidity, wind speed, solar. 

GetRealtime setup file: CIMIS-135; -27537; ET Grass; Blythe Ne, Ca Cimis; 0; 33.56,-114.67,-120,275,1; P5

The CIMIS gage is located 43.9 miles south of the Wuderground gage.

 

The daily graph comparison below includes in the title MAE, mean absolute error, which is the average of each of the unsigned daily computed ET value difference in percent..

 

 

 

ET Example for location below the Equator and ahead in Time, Windhoek, Namibia, southern Africa:

 

As an example for setting up GetMyRealtime for another part of the world, a Wundergage was selected in the southern hemisphere and before Zulu Universal Time at Greenwich, England.

 

Wunderground Gage: INAMIBIA2, computation time step=5 minute, parameters temp, humidity, wind speed, and with and with out solar for comparison.

  

GetRealtime setup file w/Solar:  INAMIBIA2; 27550; ET Grass; Namibia Africa w/solar; 0; -22.575, 17.074,15,5488,1; P5

  

GetRealtime setup file w/o Solar: INAMIBIA2; -27550; ET Grass; Namibia Africa w/o solar; 0; -22.575, 17.074,15,5488,1; P4

  

Note that the local standard meridian is +15 and that the latitude is negative while the longitude is positive, all the reverse of gages in the USA.  The seasons are also reversed so that ET will decrease during the summer... err our winter... and this station is higher in elevation than Denver, CO but still pretty arid.  Not sure what to make of 42" rainfall for Jan-May, 2011.  This is a WunderGage after all.  Looks like the return of the Boojum.  And use the 'state' code AZ in the rsite table to turn off northern daylight savings.

 

(After further review, the 42 inch rainfall was indeed a record and should scare you Yuman's socks off!)

 

The comparison for June1 to Nov 1 looks great so far but the rainy season is at hand with 20 inches of rain typical for the next 5 months and doubt is beginning to cloud the graph.  Geez I hope this works out.

 

 

 

 

 

RAINFALL:

 

Comparison of NEXRAD Radar Point and Areal Rainfall

 

As long as weather data is being collected at the above Wunderground gages I thought I would see how the NEXRAD radar N0R (N0Q after Nov 2011) computed rainfall would compare at the 6 gages.  Also the irrigated area of the 6 ag districts were palimetered using my GetMapArea.exee program and the needed radar boundary files were created for computing district wide average areal rainfall from the real-time radar images.  These district wide or canal supplying areal radar rainfall data can be used in real-time by the farmer or district to adjust water orders and save a few bucks.

 

1) Imperial Valley, CA (IID) 

2) Coachella Valley,CA (CVWD)

3) Palo Verde Valley, CA (PVID)

4) Yuma and Gila Valley, AZ (YCWUA, YID, NGVID)

5) Wellton-Mohawk Valley, AZ (WMID)

6) Parker Valley, AZ (CRIT)

 

The NEXRAD radar site is YUX south of Yuma, AZ at elevation 250 ft.  Rainfall is computed from the 5-minute N0R images using the standard WRD-88D convective Z-R relationship using GetRealtime.exe.

 

 

For additional information on NEXRAD radar rainfall using GetRealtime.exe go here.

 

 

1) Imperial Valley, CA

 

Wunderground Gage: KIPL,  radar distance=58.7 miles, scan elev=4840 ft.

IID repoted irrigated area=1,600 sqmi., rainfall mapped area=3,022 radar pixels or 834 sqmi.

 

 

 

2) Coachella Valley, CA

 

Wunderground Gage: KCAINDIO5,  radar distance=128.2 miles, scan elev=15,400 ft.

CVWD reported irrigated area=109 sqmi., rainfall mapped area=694 radar pixels or 182 sqmi.

 

 

 

3) Palo Verde Valley, CA

 

Wunderground Gage: MCBRA3,  radar distance=55.5 miles, scan elev=4,520 ft.

PVID reported irrigated area=163 sqmi., rainfall mapped area=661 radar pixels or 170 sqmi.

 

 

 

4) Yuma Valley, AZ

 

Wunderground Gage: KAZYUMA11,  radar distance=14.8 miles, scan elev=1,050 ft.

Yuma Area reported irrigated area=93 sqmi., rainfall mapped area=523 radar pixels or 125 sqmi.

 

 

5) Wellton-Mohawk Valley, AZ

 

Wunderground Gage: KAZWELLT4,  radar distance=37.5 miles, scan elev=2,780 ft.

WMID reported irrigated area=91 sqmi., rainfall mapped area=530 radar pixels or 127 sqmi.

 

 

 

6) Parker Valley, AZ

 

Wunderground Gage: MTS917,  radar distance=114.1 miles, scan elev=12,730 ft.

CRIT reported irrigated area=164 sqmi., rainfall mapped area= 569 radar pixels or 150 sqmi.

 

 

 



Some additional page links about ET and Nexrad Radar help and comparisons:

List of How To Videos on Youtube
Help Page for GetNexrad.exe
Nexrad Rainfall to Tipping Bucket Comparison
ET and Radar Rainfall along the Lower Colorado River, AZ-CA
Nexrad Rainfall-Runoff Comparison Las Vegas Valley, NV
Nexrad Rainfall-Runoff Comparison San Jouqin Valley, CA
Nexrad Rainfall-Runoff Comparisons in northwestern Arizona
Nexrad Snowfall Comparisons in western central Sierras, CA

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