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.
