ANALYSIS OF INTENSITY-DURATION-FREQUENCY RELATIONSHIPS UNDER FUTURE MODIFICATIONS OF RAINFALL DUE TO CHANGING CLIMATE FOR SELECTED CITIES OF TIGRAY, ETHIOPIA

Abstract

Extreme climate events are growing more severe and frequent; calling in to questions how prepared our water infrastructures are to deal with these changes. Current water infrastructure design is primarily based on Intensity-Duration-Frequency curves (IDF) with the assumption that precipitation extremes will remain unchanged throughout the design lifetimes of the infrastructures. However, a warming climate might change the extreme precipitation quintiles represented by the curves emphasizing the need for updating them. Thus, this study presents a generalized framework for estimating nonstationary rainfall Intensity-Duration-Frequency (IDF) curves for five cities of Tigray (Mekele, Adigrat, Axum, Shire and Humera). To provide present and future IntensityDuration-Frequency (IDF) information, historically daily and hourly rainfall data was collected and RCP2.6, RCP4.5 and RCP 8.5 climate scenarios was spatially downscaled using Statistical Downscaling Model (SDSM 4.2.9).Daily rainfall climate scenario data was generated and disaggregated in to hourly basis using regression models. Expected rainfall quantiles (XT) for 0.5Hr,1Hr,2Hr.4Hr,6Hr,8Hr,12Hr& 24Hr durations were computed at return periods of 2, 5, 10, 25, 50, and 100 years using frequency analysis. Intensity-Duration-Frequency (IDF) model parameters (A, B and C) were estimated and their performances evaluated. Mathematical relationships between Intensity-DurationFrequency of rainfall were developed for all stations for the present and future climate conditions. Percentage differences in the intensity of rainfall between the current and future climate scenarios were quantified and general trends for the 21 st century time line has established. In general, the outcomes of this study indicate that future rainfall Intensity patterns under the emerging climate change scenarios at the study cities would vary. It is expected to decrease up to maximum range of 78.61% for longer frequencies while it tends to be higher up to 65.95% at shorter frequencies for some stations. These have major implications on ways in which current and future water management infrastructures are designed, operated, and maintained. Consequently, design standards and guidelines currently employed in the study area should be reviewed and/or revised with the reflection of the impacts of climate change.