A hyetograph is a graphical representation of the distribution of rainfall over time. For example, in the 24-hour rainfall distributions as developed by the Soil Conservation Service (now the NRCS or National Resources Conservation Service), rainfall intensity progressively increases until it reaches a maximum and then gradually decreases. Where t...
instrument for recording rainfall
• (n.) A chart or graphic representation of the average distribution of rain over the surface of the earth.
Hy'e·to·graph noun [ Greek ... rain + -graph .] A chart or graphic representation of the average distribution of rain over the surface of the earth. 
hyetograph, hyetographic A chart showing the amount of rainfall.
A recording rain gauge.
a map or chart showing the average rainfall for the localities represented.