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Accueil du site → Master → Pays Bas → 2009 → Validation of TRMM rainfall data for hydrological applications in Pangani river basin in Tanzania

UNESCO-IHE Institute for Water Education, Delft (2009)

Validation of TRMM rainfall data for hydrological applications in Pangani river basin in Tanzania

Haque, R.M.F.

Titre : Validation of TRMM rainfall data for hydrological applications in Pangani river basin in Tanzania

Auteur : Haque, R.M.F.

Etablissement de soutenance : UNESCO-IHE Institute for Water Education, Delft

Grade : Master of Science (MS) 2009

Rainfall is a highly dynamic process changing often in form and intensity as it passes over a given area. Traditionally, rainfall is measured using rain gauges at ground stations. Nowadays, an increasing number of satellite based rainfall products are available in near real time over the internet. Tropical Rainfall Measuring Mission(TRMM) space borne rainfall sensor by NASA and JAXA had developed new algorithms to estimate the spatial and temporal distribution of the rainfall. The data from this sensor is treated to estimate the 3D rain distribution from the radiance in the visual spectrum, precipitation radar and microwave sensors. Rainfall estimate from TRMM are available at 0.250 x 0.250 spatial and up to 3 hourly temporal resolutions since January1998 which covers 500 S to 500 N of the tropics. This study will provide information about the ability and accuracy of the TRMM to retrieve daily and monthly rainfall compared to the ground based rainfall stations data over Pangani river basin, Tanzania. To carry out this comparison, eight years of monthly rainfall data from 1998 to 2005 for 50 gauge stations and daily rainfall data from 1998 to 2003 for 12 stations are used in conjunction with TRMM data for the same period. The comparison of TRMM grid rainfall with point gauge rainfall is done by using nearest neighbourhood method as well as bilinear weighted interpolation method. Application of bilinear weighted interpolation method has brought some improvement in the comparison results over nearest neighbourhood method. In both methods monthly TRMM retrievals corresponds reasonably well with the monthly gauge rainfall than the daily retrievals. The comparison is also carried out at sub-basin level by dividing the catchment into 7 sub catchments. The sub-basin rainfall is estimated from the gauge rainfall by the interpolation method based on distance and elevation weighting. The spatial comparison at sub-basin level has given acceptable result. The spatial distribution of yearly total rainfall map of Pangani is constructed. Comparing the consecutive yearly total rainfall maps it is seen that TRMM has reasonably captured both spatial and temporal rainfall pattern but failed to detect higher intensity rainfall close to the mountainous parts of the basin. Five statistical performance measures namely coefficient of determination, mean error (bias), root mean square error, relative root mean square error and Nash-Sutcliffe coefficient are used to quantify the accuracy of TRMM rainfall data compared to gauge rainfall data. In conclusion, TRMM has performed fairly well in monthly scale but its hydrological application in mountainous areas and heavy rainfall period still requires validation with the ground based gauge rainfall before taking it as a sole alternative.

Sujets  : rainfall measurements ; rain gauge ; river basins ; Tanzania


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