Estimation of the summer-fall PMP and PMF of a northern watershed under a changed climate

This study is focused on assessing a summer-fall probable maximum precipitation (PMP) under recent climate conditions and then applying it under a future projected climate using output information from a regional climate model. The estimated PMPs are forced into a hydrological model to investigate potential changes in probable maximum flood (PMF) values. The PMP method is based on the moisture maximization method developed by the World Meteorological Organization. Precipitable water amounts are evaluated using data from the Canadian Regional Climate Model. The approach was tested on the Manic-5 River basin in Canada. Results show the PMP intensity could increase by 0.5-6% for 48 h and 72 h PMP values by the 2071-2100 horizon. These PMP values were used to assess projected PMF values. A lumped conceptual hydrological model was calibrated under recent climate values and model parameters were kept unchanged for modeling future hydrological regimes. Hydrological modeling results indicate modest changes of the PMF values for future climate projections, with no clearly identified upward or downward trends. The study also highlighted the need for a coherent approach to estimate PMF values under future climate conditions using projected PMP estimates, since the current practice of simulating the PMF value by inserting half of a PMP six days prior to the PMP event in a meteorological time series did not produce consistent results. An approach based on a random insertion of the PMP into a meteorological time series is a promising avenue to explore.