Satellite Based Rainfall Estimation: Evaluation and Characterization With Homogeneous Rainfall Region Classification Using GIS and Remote Sensing (a Case Study of Awash River Basin)
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Date
2014-06-06
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Addis Ababa University
Abstract
The study mainly covers the delineation of Homogeneous Rainfall Regions (HRRs) and comparison of Tropical Application of Meteorological Satellite (TAMSAT) rainfall estimate with rain gauge recorded rainfall data over Awash River basin (7.8o - 12oN and 38o - 43.4oE) using dekadal rainfall datasets during the period of 2008-2010 and long year mean data(1990 -2010) available at National Meteorological Agency (NMA). TAMSAT rainfall data is satellite derived rainfall estimates available over the region generated using different satellite rainfall estimation techniques from international centers of excellence. Several methods that include descriptive and continuous statistics such as scatter plots and histograms, measures of variability that include the standard deviation and coefficient of variation, correlation coefficient, mean error, Principal Component Analysis (PCA), scree plot of eigenvalue and geostatistical kriking were used in the evaluation. The delineation result showed that Awash River basin has four HRRs because of its slight different character of receiving rainfall. The analysis result reveal that all HRRs in the basin receive a bi-modal rainfall cycle but the rainfall cycle at HRR1 is slightly near to mono-modal type rainfall. The two rainy seasons at each HRRs of the basin are Kiremt (June to September) and Belg (February to May). The monthly mean rainfall amounts were peak at HRR2, HRR3 and HRR4 during the month of August with a value of 261.3 mm, 99.0 mm and 125.0 mm, respectively. But the monthly mean peak rainfall amount at HHR1 is during July with a rainfall amount of 229.8mm. The evaluation and comparison of satellite rainfall estimate with rain gauge data showed that the mean error value between satellite rainfall estimates and rain gauge value are higher (>-10mm dekade-1) at HRR1 and HRR2 during second dekade of August where the distribution and amount of rainfall amount is high. However, the mean error value was minimum over the arid and generally low latitude areas of the region (HRR3). For the year of 2008 which is considered as relatively normal rainfall distribution year, the correlation coefficient result against the gauge record was found to be higher (r=0.73) compared to the selected years. The correlation coefficient result for the year considered as wet year (2010) is 0.52. During the relatively low rainfall distribution year (2009) the correlation coefficient result is 0.46. Generally, the result indicates the satellite estimated rainfall totally explained in better way the spatial and temporal pattern relationship of the rainfall climatology characteristics of each HRRs for dekadal, seasonal and annual cases considering the observed differences in the rainfall magnitude between the satellite rainfall estimates and gauge rainfall value.
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Keywords
Rainfall, TAMSAT, HRRs, Evaluation and Comparison