Rainfall variability assessment in the hydrological catchment of Addis Ababa

Abstract

Abstract The Intensity-Duration-Frequency (IDF) relationship is a key input for defining the hydrograph and peak flow discharge required for the hydraulic design. The IDF curves describe the relationship between rainfall intensity, rainfall duration, and return period. The objective of this study was to develop an accurate rainfall analysis in the Addis Ababa catchment. To compute reliable IDF curves, long rainfall data at fine time step scale and uniformly distributed are necessary. In Ethiopia, there is limited availability of data at sub-hourly and at spatial scales. To cope with these issues, (1) stochastic disaggregation techniques have been employed to disaggregate daily observed data into sub-hourly data and (2) to guarantee homogeneity in the project area, the merge of satellite data and observed gauged data have been considered. In this study, IDF curves have been computed for the entire hydrological catchment of Addis Ababa (~1430 km2). The results of the study include tabular and graphical presentation of IDF curves under changed climatic conditions, for return periods of 2, 5, 10, 25, 50 and 100 years for the durations of 15,30 min and 1, 3, 6, 12 and 24 hours.