Blue Nile Rainfall Experiment: Validation Results

Abstract:

The accuracy of three widely-used, near-global, high-resolution satellite rainfall products (CMORPH, TMPA-RT v7, TMPA-RP v7) is assessed over the Blue Nile River Basin, a basin characterized by complex terrain and tropical monsoon. The assessment is made using dense experimental networks of rain gauges deployed at two, 0.25°×0.25°, sites that represent contrasting topographic features: the lowland plain (mean elevation of 719 m.a.s.l.) site and the highland mountain (mean elevation of 2268 m.a.s.l.). The investigation period covers the summer seasons of 2012 through 2014. Compared to the highland mountain site, the lowland plain site exhibits marked extremes of rain intensity, higher rain intensity, lower frequency of rain occurrence, and smaller seasonal rainfall accumulation. All the satellite products considered tend to overestimate the mean rainfall rate at the lowland plain site, but underestimate it at the highland mountain site. The satellite products miss more rainfall at the highland mountain site than at the lowland plain site. The satellite products underestimate the heavy rain rates at both sites. Both sites have uncertainty (root mean square error) values greater than 100% for 3 hour accumulations of less than 5 mm, or daily accumulations of less than 10 mm, and the uncertainty values decrease with increasing rainfall accumulation. Among the satellite products, CMORPH suffers from a large positive bias at the lowland plain site, and TMPA-RP and TMPA-RT miss a large number of rainfall events that contribute nearly half of the total rainfall at the lowland plain.