Keywords: IDF equation of precipitation, pluviometer, pluviograph.
Intensity-duration-frequency (IDF) equations of rainfall have applications in the design of urban drainage works and are also used in the estimation of flows in small rural watersheds. In the present work rainfall IDF equations were created and compared based on pluviometer and pluviograph information recorded on the weather station of Chapingo during the period of 1975-2005. The methodology of creating IDF equation based on pluviograph consisted of: a) obtaining heights of rainfalls in millimeters of the studied area, for the durations of 5, 10, 15, 20, 30, 40, 60 min and for 2, 3, 4, 5, 10, 15 and 24 h, b) transforming heights to intensities, c) obtaining return periods for each intensity, and d) obtaining multiple linear regression equations. The methodology of creating IDF equation based on pluviometer was similar to the pluviograph, however the difference were the empirical relations, using as a main data the duration 24 h rainfall, the intensities for the durations of 5, 10, 15, 20, 30, 40, 60 min and for 2, 3, 4, 5, 10, 15 and 24 h were obtained, each one for different return periods. In this last step, the methodology of pluviometer carried out important errors related to the data obtained with pluviograph; however in many parts of Mexico only pluviometric information is available. A statistical comparison between both methods was performed and it was observed that IDF rainfall equation obtained with pluviometric underestimate the real IDF equation obtained with pluviograph; this error increases with the return period of the rainfall intensity