Precipitation Frequency Analysis for Hydraulic Structures Design in Sub-Basins of the Swat River Basin

Abstract

This study undertakes a comprehensive precipitation frequency analysis for sub-basins in the Swat River Basin (SRB) in Pakistan with the objective of developing resilient hydraulic structures. The SRB is highly susceptible to extreme flooding due to its highly sloping topography, intense monsoon rainfall, and rising trends of climate variability. In this context, precipitation data from 1990 to 2014 and future projections under SSP2-4.5 scenario from 2025 to 2099 were considered. HEC-SSP software was used to analyze precipitation data. Various probability distributions, such as Normal, Log Normal, Log Pearson Type III, and Gumbel, were considered. Gumbel\'s Extreme Value Type-I Distribution is considered appropriate for precipitation analysis. The precipitation analysis yielded maximum 1-day precipitation estimates with return periods ranging from 5 to 1000 years for sub-basins in SRB. From the analysis, it is evident that precipitation extremes vary in space. Marghazar-Jambail and Barikot sub-basins are found to have the highest precipitation extremes, with rainfall intensities of over 340 mm for 1000-year return periods under SSP2-RCP 4.5 scenario. These findings indicate an upward trend in precipitation extremes under future conditions. This study provides critical, evidence-based input for the design of hydraulic structures in the Swat River Basin.

Introduction

The text explains that Pakistan’s Swat River Basin is highly vulnerable to flooding due to climate change, including increased rainfall, glacier melt, and glacial lake outburst floods. Past extreme floods (notably in 2010 and 2022) highlight the growing risk, especially in rural and agricultural areas. The study emphasizes the need for improved flood management and climate-resilient hydraulic infrastructure based on scientific precipitation analysis rather than only historical experience.

The research focuses on precipitation frequency analysis using historical data (1990–2014) and future climate projections (SSP2-4.5 scenario) across 18 sub-basins of the Swat River Basin. Using HEC-SSP software and statistical distributions (with Gumbel distribution selected as the most suitable), the study estimates extreme rainfall for different return periods (5–1000 years).

Results show strong spatial variation in rainfall due to topography and climate factors. Certain sub-basins (e.g., Manglor-Sangota, Marghazar-Jambail, Barikot) are more prone to extreme rainfall, especially under future climate scenarios, while others show comparatively lower risk. Future projections indicate an overall increase in extreme precipitation, reinforcing the need to incorporate climate change into flood and infrastructure planning.

Conclusion

The significance of precipitation frequency analysis in the context of flood risk assessment and the design of hydraulic structures in the Swat River Basin is clearly highlighted in this research. The results showed that the spatial variability in extreme precipitation values over the sub-basins was quite high. The factors that contributed to this were the topography and the elevation of the area. The sub-basins that were identified in this study as high-risk areas were Manglor-Sangota, Marghazar-Jambail, and Barikot due to the significantly higher precipitation values in these areas. The comparison of historical data with the SSP2-4.5 climate scenario showed that the magnitudes of extreme precipitation values are increasing over the years. This indicates that the impact of climate change on the hydrological cycle is becoming more prominent. The significance of this research is that it provides valuable information for the planning and designing of hydraulic structures. The flood hazard in the sub-basins can be assessed individually. The appropriate return period for the design of the hydraulic structure can be determined. The significance of this research is that it provides valuable information for the planning and designing of hydraulic structures. The necessity of adopting climate-informed and localized approaches in the context of water resources engineering is highlighted in this research.

References

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Copyright

Copyright © 2026 Waqas Saleem. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.