Rainfall can be quite variable. Sometimes you can see it rain on one side of the road and not on the other. There are many ways to measure that rainfall, but by using standard instruments it is possible to track those differences. Radar and satellites are the newest methods of monitoring rainfall, but require a ground based system to verify the estimates. The oldest currently active network is the National Weather Service Cooperative Observer network. Volunteers take manual measurements and report on a daily basis. In Kansas, we have 21 centennial stations – stations that have been operating continuously since at least 1900, with over 90 percent complete records. That is a lot of observations!
Mary Knapp, Weather Data Library