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University of Twente (2019)

Satellite based rainfall and Potential evaporation for streamflow simulation and water balance assessment : A case study in Wabi watershed, Ethiopia

Alato, A.A. (Asrat Ayele)

Titre : Satellite based rainfall and Potential evaporation for streamflow simulation and water balance assessment : A case study in Wabi watershed, Ethiopia

Auteur : Alato, A.A. (Asrat Ayele)

Etablissement de soutenance : University of Twente

Grade : Master of Science in Geo-Information Science and Earth Observation 2019

Résumé
In this study streamflow simulation and water balance closure was assessed in Wabe watershed located in Ethiopia, Eastern Africa by applying the HBV Light model. Limited ground meteorological measurements restrict water resources planning and management. Such for gauged based rainfall as well as satellite-based rainfall estimates from CMORPH, ARC2, and CHRIPS, and satellite-based potential evaporation estimates from PET-20km was tested. Satellite-based rainfall estimates was compared with five-gauge stations over the entire time series, wet and dry season (2012-2016). The point to pixel approach was used at daily base and image pixel. The comparison was evaluated by detection indices, scatter plots and frequency-based statistics. The result shows the source of error for a dry was missed rain whereas for wet season was false rain. The result shows that CMORPH outperforms by detecting rainfall depth 80% in wet season and 60% in a dry season. Findings reveal that uncorrected CHRIPS matches mean annual rainfall with gauge besides underestimation at the highest elevation. ARC2 underestimates mean annual rainfall followed by CMORPH. Four bias correction schemes were tested to refine systematic errors in satellite rainfall estimates before being used for the hydrological application. The research findings show that the distribution transformation bias scheme reasonably matches gauge observations with daily accumulated error as low as 5.4mm and coefficient of correlation up to 0.64. However, the prevailing rain rate (<1mm), which accounts for 65%, was reasonably reproduced by space and time variant bias scheme. Furthermore, propagation of errors when comparing and applying bias scheme of SRE’s with poor quality gauge measurement is evaluated and verified (Gubire station). HBV Light model was calibrated following Trial and Error procedure (2012-2016) for gauge rainfall Model efficiency was evaluated by NSE = 0.72, RVE = (-2.56%), Qbias=0.97. Model validation (2009 and 2011) showed NSE = 0.77, RVE = 6.78%. Replacing in-situ ETo with satellite PET resulted in increased peak flows (RVE=2.25). Recalibrating the model with bias-corrected SRE’s resulted in minimized bias in streamflow simulation Qbias=0.997 (ARC2) and Qbias=0.994 (CHRIPS) whereas, CMORPH showed deterioration (Qbias=1.017). However, no perfect fit of base flow and peak flow could be simualed by respective SRE’s products. The mean annual water balance closure analysis result shows that water is taken from the system over a five-year period for the respective rainfall and potential evaporation forcing. However, improvement in water balance closure is shown by recalibrating bias corrected SRE’s as low as 0.09 (9%).

Mots clés : Water balance closure ; Streamflow simulation ; Distribution transformation ; HBV Light ; Satellite rainfall estimates ; Wabe watershed

Version intégrale (ITC)

Page publiée le 25 septembre 2019