Comparison of Synthetic Design Storms with Observed Storms in Southern Arizona

Historical storms with a 24-h rainfall depth exceeding 50.8 mm (2 in.) recorded in southern Arizona were compared with design storms developed both locally and by the USDA Soil Conservation Service (SCS). This study aims to evaluate if those design storms can be representative to southern Arizona. These storm depths represent the return-period storms that pose hazards considered in design. The temporal rainfall distributions, pattern index (PI), and intensity-duration relationships of the observed and design storms were compared. The comparison of the distributions and PIs of 3- or 24-h storms showed that the observed storms were diverse, and it was not clear which design storm fits best with the observed storms. The comparison of the intensity-duration relationships showed that most of the observed storms were less intense than any design storms, especially for short duration. This suggests that the application of any of the 3- or 24-h design storms would result in overestimating rainfall intensities for relatively short duration. The SCS or locally developed design storm poorly represents the temporal distribution and intensities of the observed storms.