Of all the components of the hydrological cycle, the elements of precipitation, particularly rain and snow, are the most commonly measured. Sevruk and Klemm (1989) have estimated that there are 150 000 storage rain gauges in use worldwide. It would appear to be a straightforward procedure to catch rain as it falls and the depth of snow lying can be determined easily by readings on a graduated rod. People have been making these simplemeasurements for more than 2000 years; indeed, the first recorded mention of rainfall measurement came from India as early as 400 BC. The first rain gauges were used in Korea in the 1400s AD (as a means to plan farming and set taxes), and 200 years later, in ca. 1680 in England, Sir Christopher Wren and Robert Hooke described designs for the self-recording rain gauge.