I am performing the rainfall analysis for the Konkan region Maharashtra, India. and have daily data (24 Hr.) and want to derive rainfall depth for a smaller duration. Kindly guide regarding this. Thank You...
Dear Saurabh Patil, the answer to your question lies in the 15 minute distribution of 24h rain depth (mm). When available you need an actual rainfall event and/or a (synthetic) design storm event. Based on experiences, my approach is that I select an actual storm event with a precipitation (intensity) peak in the second half of the course. This storm event does not necessary have to obtained from your study area, could be even another region or country. Alternatively the SCS/NRCS distributions can be used as well. The distribution is what matters.
Initially extrapolated equal to duration of 24 hours (1,440 minutes) according to the amount on the pluviograph and taking into account an expected increase of precipitation (due to climate change). With fixed duration of 15 minutes a set of rainfall events (depth in mm or inch and return period) can be determined.
If you have a specific event in mind, check to see if the doppler coverage is available on approximate storm intensity and distribution over time. Without any other data or observations, there is no way to know when or how long rain occurred within the 24 hour day. Knowledge of the likelihood of what type storm is apt to produce an event extreme of interest. If there are other recording raingauges, stream gauges or well log gauges in the vicinity, these could be helpful in estimating the distribution of rain through the day. If you can find examples of the likely intense storms, such as thunderstorms, monsoons, tropical events, past streamflow flood events, well logs during flood events, these might also be helpful In developing design storm(s) of a select magnitude. They make weighing and tipping bucket raingauges that can be set for 15 minute recording, or you might be able to install an unvented transducer into the storage rain gauge, and record water levels with time, adjust for atmospheric pressure, adjust for transducer volume to calibrate the container. Of course, Standard raingauges and installation design are best for research work, but dividing up daily rainfall into 15 minute parcels is not really research grade. But I say that understanding that sometimes one has to improvise and then state the limits of the results. If using well logs, avoid any wells that are in flood plains or landforms that may funnel an excessive amount of runoff or interflow to the well vicinity. With stream gauging water levels, also note that when the level reaches the floodplain elevation, the stage discharge relationship changes, so it’s best to use stream discharge values rather than water levels. If your analysis covers a watershed or basin scale, it is best to have a network of raingauges to help define the spatial changes that can be attributed to areas with substantial topographic changes.
Some areas have have long term rainfall records, and develop tables of extremes, such as maximum rainfall of varying durations, such as 15, 30, 60 minute rates, 2, 3, 4, etc. hours, one to multiple day rates or amounts. Some might have even calculated the rainfall for the 5, 10, 25, 50, 100 year etc. events. Check with your weather agencies on historical records or data.
IDF Curves by Kothyari and Garde’s Method
Kothyari, U.C. and Garde, R.J. (1992) Rainfall Intensity-Duration-Frequency Formula for India. Journal of Hydraulic Engineering, ASCE, 118, 323-336
In computation of sub-hourly precipitation, the scaling approach is the most popular. It may be simple scaling or multi-scaling. Simple scaling is more staight forward than multi-scaling. By this method, sub-hourly precipitation can be computed in a ungauged location from regionalisation approach. Literatures are available you may refer to.
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