I have to find out the rainfall over a district from IMD gridded rainfall dataset for that i have taken arithmetic average of all points lying in that district. Is it a valid approach.
Or I need to do area-average as the points near boundary will not fully contribute to that particular district.
Dear Rajan,
Yes, a grid average can be conceived as a means of estimating total rainfall across a district in situations where grid cells are thought of as uniformly distributed and entirely cover the area. It gives a quick approximation by assuming equal weights for all grid cells. On the contrary, in situations where higher accuracy is required (especially in cases of partial overlap between district boundaries and some grid cells), area-weighted averages become more appropriate as they account for the proportion of each cell falling within the district. In summary, a grid average is appropriate for quick estimates, while an area-weighted average should be used when an accurate hydrological assessment is needed.
Regarding which area-weighted method to use, there are specific criteria to consider. For detailed guidance, refer to Engineering Hydrology by Subramanya.
All the best!
If you wish to compute the total rainfall on a given area, you must be aware that the result will depend from the averaging method. I may suggest:
- to look for the method used for computing gridded data from a set of raingauge (and possibly satellite) data.
- to try different averaging methods. For areas with significant topography, the idew method (Masih, et al., 2011) is best suited for hydrologic computations.
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