Probable maximum precipitation and flood calculations for Jeddah area, Kingdom of Saudi Arabia

Probable maximum precipitation (PMP) and probable maximum flood (PMF) methods help to define extreme rainfall and discharge magnitudes for dam and reservoir planning and design aims. In this paper, probabilistic and statistical calculation approaches are presented for physically meaningful PMP amounts from 12 meteorology station annual daily maximum rainfall values in and around the Jeddah City, Kingdom of Saudi Arabia. The climate change impact is considered as 15% for future projections. The results show that the values range between 62.1 and 244.0 mm, but the climate change impact calculations vary between 71.4 and 280.6 mm. These values are used to generate regional PMP contour maps for PMF calculations, and hence, possible flood danger on Jeddah City is assessed with the support of meaningful graphs and maps. Finally, in order to appreciate how close are the calculated PMP values to the recorded maximum daily rainfall amounts, an efficiency factor is defined as the ratio of the maximum daily rainfall to the calculated past and climate effective PMPs. The frequency factor is found to vary between 2.7 and 6.6, which are rather low compared to humid parts of the world, but in good agreement in many arid and semiarid region values.