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MMWD Blog: Think Blue Marin

Welcome to our blog! Written by staff at MMWD, “Think Blue Marin” explores all things water in south and central Marin—water supplies, conservation, new projects, watershed management, and more.

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Aug 09

A Weather Station from Space

Posted on August 9, 2018 at 2:22 PM by Ann Vallee

by Christina Mountanos

Last month a few of us in the Water Conservation Department journeyed out to the far end of the driving range at Peacock Gap Golf Course for a quick refresher on how to care for our California Irrigation Management Information System (CIMIS) weather station. We met with a representative from the Department of Water Resources (DWR), who recently equipped the core of the weather station with a new data logger, and upgraded some of its other measuring components, too.

Our field trip made me realize that we often reference evapotranspiration (ET) in our Weekly Watering Schedule blog, but seldom mention how it’s actually measured and, specifically, how MMWD measures it. See the picture below and you’ll see the stately, robotic-looking weather station that does just that for us. The technology behind it is very cool, and it’s always a treat to physically visit the site; it’s fun for me to explore this particular technical aspect of our job.

As you may know, evapotranspiration (the combined amount of water that evaporates and transpires from soil and plants) is dependent on five main factors: solar radiation, temperature, humidity, wind and precipitation. Accordingly, our CIMIS weather station has devices that measure each of these factors. For example, the contraption that looks similar to a beehive is what measures temperature and humidity. (You may see a mini version of this if you have a smart controller with its own weather station.) The arm with a flat metal plate at its end has a device on it that measures solar radiation, and it’s called a pyranometer. The arm just behind and below that with the cupped, spinning component—an anemometer—measures wind speed. Finally, the cylinder/funnel-shaped piece of equipment that sits high up on the station measures rainfall. All of these components need regular cleaning and care to ensure they are measuring accurately and transmitting the correct data, hence our recent refreshment training. (You might also notice the solar panel on the base, which is what powers the station.)

The CIMIS station collects data daily and the data is uploaded online. Each week before sending out the Weekly Watering Schedule, we tally daily ET amounts from the CIMIS website, total them together (for a weekly total) and then plug them into special equations that determine suggested minutes for watering. In a nutshell, that’s the process.

And, just to leave you with a couple of last notes that you may find interesting: To measure accurately, CIMIS stations need to be placed in an open area (where buildings or trees will not affect wind speed), on top of maintained, cool-season grass. This is why stations are often located on golf courses. MMWD’s station is actually part of a much larger collection of about 145 weather stations in California, all managed by DWR since 1985, and created in an effort to encourage smarter irrigation practices. 

If you’d like to learn more about CIMIS and other details about the California network of weather stations, you can read more on the official CIMIS webpage

I hope you find this technology as interesting as we do!

CIMIS station


Anonymous User
August 14, 2018 at 7:41 AM
Thank you for expanding my knowledge of this local and statewide system. Alice Bachelder

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