Project Objectives
The primary goal of this study was to determine the Probable Maximum Precipitation (PMP), develop rainfall frequency relationships (AEPs), evaluate potential climate change impacts on rainfall extremes, evaluate Paleoflood conditions to validate the hydrologic and rainfall-runoff analyses, and model the hydrologic response of the mine basin under extreme rainfall scenarios. Results were used to assess infrastructure vulnerability, inform design flood conditions, and guide future planning and water management strategies.
Methodological Approach
AWA applied a comprehensive, storm-based approach consistent with U.S. National Weather Service and World Meteorological Organization (WMO) guidance for PMP estimation. Historical extreme rainfall events from across Saudi Arabia, North Africa, and the Middle East were analyzed using AWA’s Storm Precipitation Analysis System (SPAS). Each storm was maximized for available moisture, transpositioned geographically, and adjusted for orographic influences through the Geographic Transposition Factor (GTF). The resulting PMP depths were calculated for durations from one to seventy-two hours across a one-square-kilometer grid resolution.
Annual Exceedance Probabilities (AEPs) and Intensity-Duration-Frequency (IDF) relationships were developed from regional station data and satellite reanalysis products using L-moment statistical techniques. These were integrated with the PMP results to supporting both deterministic and risk-based flood analyses. provide probabilistic rainfall estimates across a wide range of recurrence intervals.
Hydrologic and Paleoflood Analysis
A detailed hydrologic assessment was completed using HEC-RAS modeling to evaluate rainfall-runoff processes, flood routing, and inundation extents. The analysis incorporated PMP and AEP rainfall inputs and paleoflood evidence to establish upper limits of historical flood magnitudes.
Climate Change Assessment
Downscaled CMIP6 model projections were used to evaluate potential future changes in temperature, precipitation, dew point, wind speed, evaporation, and other parameters under multiple emissions scenarios (SSP2-4.5 and SSP5-8.5). Analyses indicated minimal change in short-duration, high-intensity rainfall events, suggesting that existing PMP values already encompass the physical upper limit of potential storm moisture. However, moderate increases (5–15%) were projected for longer-duration precipitation totals (30–90 days) by 2100, potentially affecting water balance and storage management considerations.
Key Findings
• The Jabal Sayid region exhibits a dry desert climate with infrequent but occasionally intense convective rainfall. • PMP estimates reflect the physical maximum rainfall possible over durations from 1 to 72 hours, accounting for local topography and storm dynamics. • AEP and IDF analyses provide rainfall magnitudes from frequent to extremely rare events (100-year to PMP-level). • Hydrologic simulations identified localized areas where infrastructure could be impacted under extreme flood conditions. • Climate projections show limited impact on PMP magnitudes but gradual increases in multi-day rainfall totals, temperature, and evaporation rates. • The paleoflood study validated flood extents consistent with modeled PMP-based inundation patterns.
