Estimation of Probable Maximum Precipitation (PMP) Using in-Situ and Reanalysis Global Precipitation Products (A Case Study on Uapper Blue Nile Basin (Ubnb))
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Date
2016-06
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Addis Ababa University
Abstract
Probable Maximum Precipitation (PMP) is defined as theoretically the greatest depth of precipitation for a given duration that is physically possible over a given size storm area at a particular geographical location at a particular time of year. The PMP for rainfall stations in Ethiopia have been estimated by Hershfield statistical method with frequency factor (K) determined by the Hershfield’s chart. But the chart was originally developed by using over 2,700 metrological stations ninety percent of which were taken from USA which might not give reliable estimates for a country like Ethiopia having different climatic conditions with that of USA. Therefore, the objective of this study was to evaluate the frequency factor obtained from the Hershfield’s chart and to provide fresh and reliable estimates of PMP using in-situ and ECMWF, ECMWF bias corrected & GLADS reanalysis global precipitation products for UBNB and then evaluate PMP value of reanalysis global precipitation products with the in situ PMP value. The study shows both in-situ and reanalysis products for 1 day, 2 & 3 days the Km and PMP (mm) value are not more than 11 and 875 respectively and GLADS precipitation product is adequately capture PMP with respective to the in situ PMP result, and both ECMWF & ECMWF bias corrected reanalysis precipitation products are inadequate to capture PMP value under this study area. Therefore, for ECMWF and ECMWF bias corrected reanalysis precipitation product required data down scaling or other major data improvement technique to capture PMP value adequately. Whereas, the computed PMP value as a sub basin of UBNB are shown, three of them of the reanalysis products are not adequately captured the PMP value with respective to the in-situ PMP value, so, the reanalysis products as sub basin of UBNB are not practicable it needs minor and major data improvement techniques. In UBNB also comparison of the PMP value using the new Km and the chart values for both in situ and reanalysis products exhibited difference 38 up to 96.4%, this result confirmed the Hershfield’s chart overestimated PMP value which leads to uneconomical designs. The average ratio of the PMP to the 10,000 years return period quantiles for in situ, ECMWF, ECMWF bias Corrected and GLADS precipitation product for study area was found to be about 1.7,1.6,1.8 and 1.3 respectively. this shows ECMWF, ECMWF bias corrected and GLADS products are adequately captured the result of average ratio value of the in situ data.
KEY WORDS: PROBABLE MAXIMUM PRECIPITATION, UPPER BLUE NILE BASIN, HERSHFIELD STATISTICAL METHOD, and REANALYSIS GLOBAL PRECIPITATION PRODUCTS.
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Keywords
Probable Maximum Precipitation, Upper Blue Nile Basin, Hershfield Statistical Method, Reanalysis Global Precipitation Products