How well can we measure precipitation? Why is it so important? - Ali Tokay

Weather fascinates people and it is something we talk about every day.  It is interesting to note that we mostly complain about the weather: too cold, too hot, too wet.  For some reason, we do not acknowledge the weather when there is a sunny and comfortable day to do outdoor activities.  We get quickly disappointed if the weather does not meet the forecast, especially if the forecast was sunny but precipitation falls from the sky. 

First, what is precipitation? Precipitation is defined as any product of condensation of atmospheric water vapor that falls under gravity.  Precipitation is a generic term for drizzle, rain, sleet, snow, hail.  So, precipitation can be liquid or solid forms of water.

Second, why are weather forecasts wrong? Weather forecasts are based on complex mathematical equations where the variables are determined through observations such as precipitation amount and intensity.  So, precipitation measurement is important for weather forecasting.

What else, precipitation is a resource of fresh water.  We do not only use water for our daily needs, we use water to produce energy.  While we have to educate ourselves when it comes to use of water, we should also have a good idea about how the fresh water is distributed across the globe.  Most of the fresh water reaches the ground as rain, and rain gauges are the direct resource to measure the rainfall.

However, rain gauges provide a point measurement and we need to know rain’s global distribution.  This is where we need other measuring instruments beyond rain gauges.  Weather radars are excellent resource for measuring distribution of rainfall within their coverage, which can extend to coastal areas.  Weather satellites are the sole resource to measure rainfall over the vast majority of oceans.  But, both radars and satellites do not measure rainfall directly. Instead, rainfall is estimated from their measured quantities.  Since it is an estimate, it requires validation, or checking for accuracy.  So, we need rain gauge measurements where we can to validate weather radar and satellite rainfall estimation. 

So, rather than complaining about weather on a rainy day, why not measure the rainfall?  I have to confess that I did not measure the rainfall when I was growing up.  Well, we first did not know about how important fresh water is for the climate.  Today is a communication age.  It is far easier to learn about our surroundings including the environment.  It is a great science fair project to measure the rainfall at home and compare with the nearest official report.  This will teach us how good we measure rainfall and how variable rain is.  We should make sure that our measurements are taken in an open space and we should record the rain amount and time of observation.   If you have an open secure place, it might be even better to measure rainfall at two or three locations or even with side-by-side rain gauges, such as shown in the image of a rainfall measuring farm below.  While this farm has more sophisticated rain measuring devices, a simple bucket with a ruler should do the job.

By the way, if you go to Europe and mention rain gauge, folks may not understand what you are talking about.  Europeans mostly know a rain gauge as a pluviometer.  Also, they do not use inches as we do for the rainfall amount.  They say kilogram per meter square and even in Canada, they use millimeter not inches.  Please note 1 inches = 25.4 millimeters and 1 millimeter = 1 kilogram per meter square.