The impact of climate change on rainfall Intensity-Duration-Frequency (IDF) curves in Alabama

Changes in the hydrologic cycle due to increase in greenhouse gases are projected to cause variations in intensity, duration, and frequency of precipitation events. Quantifying the potential effects of climate change and adapting to them is one way to reduce vulnerability. Since rainfall characteristics are often used to design water management infrastructures, reviewing and updating rainfall characteristics (i.e., Intensity-Duration-Frequency (IDF) curves) for future climate scenarios is necessary. This study was undertaken to assess expected changes in IDF curves from the current climate to the projected future climate. To provide future IDF curves, 3-hourly precipitation data simulated by six combinations of global and regional climate models were temporally downscaled using a stochastic method. Performance of the downscaling method was evaluated, and IDF curves were developed for the state of Alabama. The results of all six climate models suggest that the future precipitation patterns for Alabama are expected to veer toward less intense rainfalls for short duration events. However, for long duration events (i.e., >4 h), the results are not consistent across the models. Given a large uncertainty existed on projected rainfall intensity of these six climate models, developing an ensemble model as a result of incorporating all six climate models, performing an uncertainty analysis, and creating a probability based IDF curves could be proper solutions to diminish this uncertainty.