Evaluating the Impact of Climate Change on Rainfall Intensity-Duration-Frequency (IDF) Curves in Alabama Using Dynamically-Downscaled Precipitation Data
Type of Degreedissertation
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Rainfall intensity-duration-frequency (IDF) curves are extensively used for hydrologic designs. A design based on inaccurate rainfall characteristics can lead to malfunction of infrastructure, excessive design cost, and loss of life. It is expected that the frequency and magnitude of future extreme rainfalls will change due to increases in greenhouse gas (GHG) concentrations. Quantifying potential effects of climate change by reviewing and updating IDF curves for future climate scenarios and adapting to them is one way to reduce vulnerability. This study was undertaken to evaluate expected changes in IDF curves from the current climate to the projected future climate. Six combinations of global and regional climate models were used to develop the IDF curves under future climate scenarios. Three-hourly precipitation data were temporally downscaled using two different disaggregation methods: stochastic and artificial neural network (ANN). In the second chapter, stochastic method was used to downscale three-hourly precipitation into 15-min precipitation amount and IDF curves were developed. The results of all six climate models suggest that the future rainfall intensities are expected to decrease for short duration events (i.e., less than 2 hours). However, for longer duration events, the results are not consistent across the models. In the third chapter, a feed-forward, back- propagation ANN model was developed to estimate maximum 15-, 30-, 45-, 60-, and 120-min precipitations. The results were also compared with the disaggregated rainfalls derived using the stochastic method.Results indicate that future rainfall intensities for short duration (< 2 hours) events are expected to decrease by 33% to 74%. However, a large uncertainty exists in the projected rainfall intensities of longer duration events. In chapter 4, uncertainty associated with the studied models was quantified using kernel density estimator and probability-based IDF curves were created. The resultant IDF curves incorporating all models were also developed. Although the results derived from different climate projections show large uncertainty associated with climate models, all of them indicate decrease in future rainfall intensity for short duration rainfall events, especially for durations less than 2 hours. The methodology developed can be used for developing IDF curves for other parts of the United States and the world.