Regarding the use of Monthly Maximum Rainfall Intensity data, you need to think about the application for your IDF curves and then decide whether to due Partial Duration Series (looking at all values, or Monthly Maximums.  When  you take only the largest rainfall in a month, you eliminate other high values that may be also be detrimental to your objective function.  For example, if you are looking at scour in streambeds, and you have two large storms in a month, both will produce significant scour, but if you use only Monthly Maximum data, you neglect the second storm; hence you show lower frequencies for each rainfall intensity than if you do a Partial Duration Series analysis, and you underestimate the frequency with which your objective function is subjected to a given rainfall intensity. 
 
I think that I am not saying this well (this is my first day back after the holidays), but if your objective function is susceptible to SEQUENTIAL DAMAGE or degradation from multiple storms of a given intensity, then you should use partial duration series.  Examples are streambed scour (noted above), frequency of combined sewer overflows,  frequency of overflow of detention basins, etc.  However, if one storm of the above a certain intensity creates FAILURE of your objective function, (loss of the dam for a storage facility, washout of a road, flooding that destroys infrastructure, etc.) then it is OK to use Monthly Maximums.
 
Hope this is helpful, Happy New Year...LAR 
 
 -----Original Message-----
From: A list for discussion and information exchange concerning the research, pla [mailto:[log in to unmask]]On Behalf Of Ir Chong Sun Fatt
Sent: Friday, December 28, 2001 2:59 AM
To: [log in to unmask]
Subject: Derivation of IDF for Frequent Storms using Monthly Maxima Data

Dear Members,
 
I am currently trying to develop Intensity-Duration-Frequency (IDF) curves for frequent storms ( return periods of 2, 3, 6, 12, 18 & 24 months ) for various urban centers in Malaysia, a country which experiences humid tropical climate. I intend to use conventional Frequency Analyses ( Gumbel, Pearson, GEV, GLO, etc ) on " Monthly Maximum Rainfall Intensity Data " of various durations , to derive the said IDF values . This method is analogous to the derivation of IDF values using Annual Maxima Series for return periods >= 2 years.
 
I wish to solicit advisories and comments from fellow members as to the appropriateness and suitability on the proposed methodology. Suggestions on more suitable methods are also welcome.
 
Thank you.
 
Mr Chong Sun-Fatt,
Hydrology Engineer,
Department Of Irrigation And Drainage,
Malaysia