Uncertainty Analysis of Probable Maximum Flood in Bakhtiari Dam Basin Due to Uncertainty in Probable Maximum Precipitation, Air Temperature and Initial Snow Water Equivalent

The reliability and validity of extreme floods, especially the Probability Maximum Flood (PMF), cannot be ensured without considering the uncertainties in flood estimation. Input variables in rainfall-runoff models include precipitation, air temperature, and initial Snow Water Equivalent (SWE) are sources of uncertainty in flood forecasting and estimation. In this paper, the fuzzy set theory method is used to propagate uncertainty of PMP, air temperature and initial SWE for estimating PMF in Bakhtiari Dam Basin in southwestern Iran. The results show that the uncertainty of PMF hydrograph peak discharge due to uncertainty of PMP is more than the uncertainty of PMF hydrograph volume. The uncertainty of the PMF hydrograph volume due to the uncertainty of air temperature and initial SWE is more than the uncertainty of the PMF hydrograph peak discharge. So that the uncertainty of PMF hydrograph peak discharge due to uncertainty in PMP, air temperature and initial SWE equal to 10% were ±10.2%, ±7.6% and ±0.18% respectively. Also the uncertainty of PMF hydrograph volume due to uncertainty in PMP, air temperature and initial SWE equal to 10% were ±8.0%, ±9.8% and ±0.35% respectively. Therefore, in order to reduce the uncertainty in estimating PMF, it is necessary to be more careful in estimating PMP, air temperature and initial SWE values respectively.