A methodology to evaluate probable maximum precipitation (PMP) under changing climate conditions

Applied Weather Associates (AWA) has conducted numerous site-specific, regional, and statewide Probable Maximum Precipitation (PMP) studies throughout the world using a deterministic storm based approach. Recently, a lot of questions have been raised on how climate change may affect PMP. As a result, numerous AWA PMP studies now address the potential effects of climate change on the estimation of PMP and probable maximum flood (PMF) studies. However, there is not a specific methodology in the scientific community to estimate climate change effects on PMP. Estimating PMP without accounting for climate change may have the risk of underestimation/overestimation. Future climate simulations indicate that an increase in temperature and dew point/precipitable water are likely. The question remains on how this will affect extreme precipitation events used for PMP/PMF.
In this paper, simulation outputs from the Coupled Model Intercomparison Project Phase 5 (CMIP5) are used to develop a methodology to investigate trends in extreme precipitation utilizing frequency analysis estimation, storm maximization, and the estimation of PMP while accounting for changing climate conditions. Climate change scenarios are based on various Representative Concentration Pathways (RCP) adopted by the Intergovernmental Panel on Climate Change (IPCC) fifth Assessment Report. Model projections used for climate change sensitivities not only affect precipitation and temperature but also the monthly maximum precipitable water, and the ensuing maximization ratio used for the estimation of PMPs. Precipitable water represents one of the key variables in the estimation process of PMPs. This presentation will provide discussion on the methods developed, discussion of trends in extreme precipitation, and whether these extreme precipitation events are expected to change in intensity and/or frequency in the future.