Are Satellite-Gauge Rainfall Products Better than Satellite-Only Products for Nile Hydrology?

Abstract

The objective of this study is to compare the performances of two rainfall products (with resolutions of 3-h, 0.25°×0.25°) developed by the Tropical Rainfall Measuring Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA) method: TMPA 3B42RT (a real-time version that does not include any rain gauge data) and TMPA 3B42 (a research version that combines TMPA 3B42RT with global rain gauge data). These products are separately used as input into the SWAT hydrological model to simulate daily streamflow for two adjoining watersheds (Koga with drainage area of 299 km2, and Gilgel Abay with a drainage area of 1,656 km2) in the Ethiopian part of the Nile basin, and the simulations are then compared to observed streamflow. Results turn the conventional notion on its head: the satellite-only TMPA 3B42RT products are found to be much better than the satellite-gauge TMPA 3B42 products in terms of their ability in reproducing daily streamflow. Nile hydrologist are advised to use TMPA 3B42RT over TMPA 3B42. Algorithm developers are advised to take a deeper look into their bias adjustment techniques especially in mountainous topography and rain gauge sparse regions.