Did you know that we can measure precipitation in a direct way only with a rain gauge?Even though most of the images you see in TV weather forecast are generated from radars or satellites, what they measure are actually proxy variables like radar reflectivity or cloud-top brightness. As a result, only-remote-sensing-derived precipitation estimates include inherent large errors, so the estimates have to be evaluated and/or corrected by gauge-derived measurements.
Then, why aren’t we satisfied with rain gauges? Why are we spending lots of efforts to pursue the proxy precipitation data? The first problem is that we can’t just cover the entire Earth with gauges; it is hardly possible to install enough gauges, for example, in mountainous regions or over ocean surfaces. Meanwhile, more concerns about climate change require weather data on a global scale. Relying on only gauge data entails a spatial resolution problem, or “uncertainty”, since a gauge can represent a point precipitation, as opposed to radar/satellite which can represent areal precipitation.
Did you know that?
If all of the rain gauges throughout the world were put together, they would only cover the area of two basketball courts. Source: NASA PMM.
Another problem is that there are so many factors which contribute to “errors” in the gauge measurements. Owing to wind-induced error, for example, precipitation is generally underestimated since a gauge fails to catch wind-blown (light intensity) rain and snow. In other cases, high intensity rainfall can overflow from a gauge which, likewise, leads to underestimated measurements.
Nevertheless, almost every country operates rain gauges for weather forecast and research purposes. How come? First, as mentioned before, rain gauges can measure precipitation directly on the ground. Second, gauges are cheap, easy to manage and super easy to use; just put a bucket in your backyard and read a number!
Besides, rain gauges have a longest record history among other rain observation systems, which is important when it comes to climate research. Whilst the first tipping-bucket gauge (most common gauge type for national weather stations) was invented in 1662 in Britain, satellite observation does not extend back beyond 1974 .
Did you know that?
Even earlier gauge measurements were recorded by a Korean rain gauge, Cheugugi (측우기) in 1441. However, the gauge data are not reliable since they were used for rice taxation and therefore often manipulated.
Have you thought about having rain gauges as many as possible to overcome its shortcomings? There have been attempts to form a special network of gauges, such as ‘WegenerNet‘ in south-eastern Austria (let me know if you know any other high density weather networks for precipitation measurements!). The WegenerNet has 153 weather stations, of which 150 have a tipping-bucket gauge, in an area of 15 x 20 km; there are only two Austrian national stations (ZAMG) in the same area. Such a dense network is expected to provide more accurate data (at least for the covered area), especially in terms of uncertainty, which can be used for regional precipitation studies but also for radar/satellite estimates evaluation as a ground ‘true’ reference.