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Development of an isopluvial atlas for Egypt using statistical and GIS-based methods

El-Sayed Eman Ahmed Hassan

Meteorology Hydrology and Water Management. Research and Operational Applications

2025

Vol. 13, Iss. 1

1--19

Rainfall across various climatic zones of Egypt, including arid coastal and semi-arid inland regions, exhibits significant temporal and spatial variability. Precise estimation of effective rainfall depths is essential for design engineers, hydrologists, and consultants involved in the construction of hydraulic structures such as dams, lakes, culverts, and diversions. Moreover, rainfall depth plays a crucial role in the design of urban drainage systems, small-scale irrigation projects, and broader water resource management initiatives. To address this need, an atlas of isopluvial maps for Egypt was developed using statistical methodologies and Geographic Information System (GIS) tools. This study employed short-duration rainfall data from various climatic zones of Egypt to create an empirical formula for estimating short-duration rainfall depths. Maximum annual daily rainfall data from 54 stations were analyzed to estimate short-duration rainfall values. The analytical process used Gamma distributions to determine maximum rainfall depths for various return periods and durations. The derived empirical formula and daily rainfall data were then incorporated into a GIS framework for spatial interpolation and the generation of isopluvial maps. The resulting atlas provides isopluvial maps for return periods ranging from 2 to 200 years and durations from 5 minutes to 24 hours. These maps serve as a valuable resource for decision-makers and design engineers, providing reliable rainfall estimates for specific locations or regions across Egypt. Additionally, the methodology presented in this study offers practical guidance for understanding and modeling the temporal and spatial distribution of rainfall in diverse climatic regions; its potential for improving the design of hydraulic structures is highlighted. Further validation of the atlas using independent datasets is recommended.

Estimating the runoff coefficient using the analytic hierarchy process

Lallam F., Megnounif A., Ghenim A. N.

Journal of Water and Land Development

2018

no. 38

67--74

The runoff coefficient (RC) is a parameter that is very often used in surface hydrology in order to characterize the drainage capacity of a watershed. The traditional estimate of this coefficient is often made from abacuses based on 2 or 3 parameters to the maximum. In this work, three numerical models are presented. Two models are based on experimental work. The first one is based on three criteria, namely the vegetation cover, the type of soil, and the slope. The second one considers the size of the watershed, the maximum daily rainfall and the type of soil. In practice, it is not easy to estimate the coefficient of runoff by simultaneously considering the influence of several criteria. In order to overcome this problem, a third model is developed and presented; it allows capitalizing the information from the first two models mentioned above. The objective of the present work is to be able to verify the comparability of these criteria and to assess the relative importance of each of them.

Współczynnik odpływu (RC) jest parametrem często używanym w hydrologii wód powierzchniowych w celu charakterystyki zdolności drenarskiej zlewni. Tradycyjnie ocenę tego współczynnika wykonuje się za pomocą obliczeń bazujących maksymalnie na 2–3 parametrach. W niniejszej pracy przedstawiono trzy modele numeryczne. Dwa z nich oparte są na badaniach eksperymentalnych. Pierwszy bazuje na trzech kryteriach: pokrycie roślinnością, typ gleby i nachylenie terenu. Drugi uwzględnia rozmiar zlewni, maksymalny opad dobowy i typ gleby. W praktyce nie jest łatwo ocenić współczynnik odpływu przez uwzględnienie wpływu kilku kryteriów równocześnie. Aby rozwiązać ten problem, zbudowano i przedstawiono trzeci model. Umożliwia on połączenie informacji z dwóch wyżej wymienionych modeli. Celem pracy jest umożliwienie weryfikacji porównywalności kryteriów i dokonanie oceny względnego znaczenia każdego z nich.