On the Local-Scale Spatial Variability of Daily Rainfall in the Highlands of the Blue Nile: Observational Evidence

The HEXB (Hydrological EXperiment in Blue nile) experiment provided an opportunity, via dense network of rain gauges, to study the spatial variability of daily rainfall at a 5 km x 5 km scale in a tropical and mountainous part of the Blue Nile river basin, for the period of July 1 – August 9, 2008. The results of daily rainfall spatial analyses are shown in this paper. High intensity rainfall events have more absolute spatial variability (e.g., standard deviation) and less relative spatial variability (as measured by coefficient of variation), compared to lower intensity events. The coefficient of variation varies from 12% to 320%, with a median of 50%, indicating that there is a significantly large variability from one gauge observation to the other, and one gauge does not represent 5 km x 5 km grid-average daily values. A careful rain gauge layout design is critical to get accurate estimates at smaller number of rain gauges.