Creating a robust annual rainfall measurement for your land is easy and cheap using this citizen-science project

Your Land’s Water Story

Unravel your land’s water mystery for $48

A simple and dead-accurate rain gauge to record exactly how much precipitation your farm, ranch, or homestead gets on an annual basis. Photo from back deck.

Do you know exactly how much water your land received last year? Or possibly even more importantly, do you know the average amount of rain your land is likely to receive? Rain averaged over weekly, monthly, and annual time periods plays an oversized role in deciding how we should manage our land.

No single weather variable is spoke about more in diners, feed stores, and on local news than precipitation. While precipitation can come in the liquid (rain) or solid (snow) variety, annual average rainfall can be normalized by using the liquid equivalent, i.e. inches or centimeters of rain per year.

Why does knowing exactly how much rain and snow your land received matter so much? Because without knowing your exact rain amounts, you are unable to connect patterns from year-to-year related to vegetation growth which relates to sustenance for your animals, your wildfire risk, your waterway health and productivity, and the ideal timing for prescribed fire, should you choose to put fire on your own land. Further, if you’re like me and harvest your own rainwater, knowing the timing and amount of rainfall helps you utilize as much of that rainwater as possible during the dry periods.

A $48 solution to measure your annual rainfall

What if I told you that for $48, you could own all the equipment necessary to create your own rain climatology for your land? And you would be helping government agencies and researchers alike study weather and climate in your area? Behold the Community Collaborative Rain, Hail & Snow Network (CoCoRaHS) rain gauge; a simple yet dead-accurate 4-inch diameter rain gauge made of plastic, as shown in the top image of this article. The three-piece gauge contains a graduated cylinder that holds one inch of rain. The entire gauge is capable of holding about 11 inches of rain in total and can even be used to measure snowfall.

Each day, thousands of CoCoRaHS citizen scientists submit their precipitation reports across the US. Image from https://maps.cocorahs.org/

I think an obvious question that a lot of readers of this article will ask, “Why is a manual rain gauge a more ideal solution with all of the automatic weather stations available?” A CoCoRaHS rain gauge has no moving parts and is exceptionally accurate. Automatic rain gauges, the most common of which is a tipping bucket, are prone to underestimating intense rainfalls due to spillage over the bucket side. One study found a 40% error when the rainfall rate reach 2.6 inches/hour (600 mm/hour). Although this rate of rainfall is rare, it is possible you could be missing several percent of your annual rainfall due to this type of error.

Another advantage of the simple CoCoRaHS rain gauge is the ability to collect snow using the same instrument. All you need to do to collect snow in your CoCoRaHS gauge is to remove the funnel and graduated cylinder from the main rain gauge body which leaves a 4-inch diameter cylinder. Then you bring the gauge into your house to warm and melt the snow. Most consumer-grade weather stations do not have the ability to measure snow.

Lastly, checking your CoCoRaHS rain gauge makes you inherently connected to your land. There’s nothing like waking up in the morning and heading straight outside to see how much precipitation the planet has gifted you with. But if you’re gone for a vacation, are an absentee landowner, or simply too busy to check your rain gauge daily, you can simply submit a multi-day report that spans up to 60 days for your station. In the Mediterranean climate of California, you typically do not see rain for months at a time; it is not necessary to submit daily “zero” reports. You simply submit one multi-day report covering up to 60 days with the sum total of precipitation in your gauge.

iOS and Android CoCoRaHS apps makes daily reporting pretty simple and convenient. You can also submit reports via the CoCoRaHS website and view your station analytics.

Your land climatology from CoCoRaHS for free

By maintaining a CoCoRaHS station, you automatically can latch into a beautiful dashboard of your precipitation climatology for free. I have provided a few example years of my annual measurements below, along with commentary in the image captions, to show how the climatology helps me relate to my land.

This was the first year I owned my farm and it was a pretty slim water year, with only about 60% of normal rainfall.

The 2021–2022 was a pretty normal water year for my property. This was a good benchmark year to see how the creek that runs through my property and fills up the adjacent pond behaves during a “normal” year.

The 2022–2023 was a crazy water year for much of California. We got two seasons’ worth of rain in a single season. Truly remarkable.

What can you do with your rain climatology?

To give you an idea of the power of maintaining your own precipitation climatology, I have included a rainwater catchment system that I recently designed and built on my farm. Using my CoCoRaHS station history and some simple Python code in a Jutpyer Notebook, I used my daily precipitation reports for my farm to simulate how much water I could obtain from a rainwater tank connected to my home-roof gutters.

The daily observations of rain from my CoCoRaHS gauge helped me pick the right size rainwater catchment storage tank and completely eliminated any guessing about how much rain my land actually received. Because I knew exactly on what days the rain came, I did not have to make any simplifying assumptions related to splitting daily rainfall across monthly averages. As I expand my rainwater catchment storage capacity on my land, I will continue to utilize my CoCoRaHS dataset to operate my rainwater catchment system more like a hydraulic-dam operator; the CoCoRaHS dataset makes this possible.

In my rainwater catchment simulation, I calculated or assumed for my farm:

• One inch of rain on the roof of my house equates to 2,207 gallons (!) of water collected
• Daily use of the collected rainwater on a 25' x 50' gardening plot at one inch of water per week or 110 gallons/day
• Garden watering only occurs between May and October

Rainwater catchment simulation for my farm using the daily precipitation totals from my CoCoRaHS rain gauge data. This simulation assumes a 5,000 gallon tank, my roof which is 3540 ft², and about 110 gallons/day use during the gardening season to water a 25'x50' gardening plot with one inch of water per week.

As you can see in the plot above, in the Mediterranean climate I live in, water is either a feast or famine throughout the year. Basically one winter storm completely fills the rainwater catchment tank with only 2–3 inches of rain. And since I am not gardening in the winter, there is little demand for the collected rainwater. To increase the utilization of my collected rainwater, I have started water wintertime cover crops that still need water due to poor soil conditions. The CoCoRaHS dataset for my farm made all of this analysis and insight possible.

Getting started with CoCoRaHS in 3 easy steps

You can start building your own rain dataset for your own farm, ranch, or homestead for $48. It is as easy as:

1. Buy and install an approved CoCoRaHS rain gauge (e.g., this gauge)
2. Apply to be a CoCoRaHS observer
3. Start making observations

There is no other cost associated with creating a reference-grade rain climatology for your land. And you’re contributing to a citizen science project that helps everyone in your community have more accurate information about their weather and climate. Here are some outstanding CoCoRaHS YouTube training videos to help you get you started.