Geospatial Rainfall–Runoff Modelling and Hydrological Assessment of an Ungauged Arid Mountain Catchment Using GIS and HEC-HMS

Abstract

Reliable hydrological information is essential for sustainable water-resource planning in arid and semi-arid environments where rainfall is highly variable and hydrometric networks are sparse. The present study evaluates rainfall–runoff processes within the ungauged Deh Desvi catchment located in the Khirthar National Range of Sindh Province, Pakistan. An integrated framework combining Geographic Information Systems (GIS), Remote Sensing, Digital Elevation Models (DEMs), spatial rainfall interpolation, and Hydrologic Engineering Center-Hydrologic Modeling System (HEC-HMS) was employed to quantify runoff generation and hydrological response. A 30 m Advanced Land Observing Satellite (ALOS) DEM was used for watershed delineation and extraction of hydrological parameters, while precipitation data from the Pakistan Meteorological Department were utilized to simulate runoff during a major monsoon event occurring from 8–10 September 2025. The study catchment covers approximately 818.5 km² and represents a typical arid mountainous watershed characterized by steep slopes, sparse vegetation cover, ephemeral drainage networks, and limited infiltration capacity. Hydrological modelling using the Soil Conservation Service Curve Number method indicated that a total rainfall of 116 mm generated 63.97 mm of effective rainfall and produced a peak discharge of 189.5 m³ s⁻¹. Approximately 55% of total precipitation was transformed into direct runoff. Hydrograph analysis demonstrated a rapid rise and recession response typical of flashy arid watersheds. Results further revealed that catchment topography, antecedent soil moisture, and rainfall intensity exert significant control over runoff generation. The findings demonstrate the applicability of GIS-integrated hydrological modelling for ungauged arid catchments and provide a scientific basis for rainwater harvesting, flood mitigation, groundwater recharge enhancement, and climate-resilient watershed management in the Khirthar mountain region. The study contributes toward addressing hydrological information gaps in data-scarce environments and supports sustainable water-resource development under changing climatic conditions.

Keywords: GIS, HEC-HMS, ungauged catchment, rainfall–runoff modelling, rainwater harvesting.