| Abstract | Karak and Bannu districts in Khyber Pakhtunkhwa, Pakistan, face a deepening water crisis driven by unreliable rainfall, declining groundwater, and growing agricultural demand. Despite receiving seasonal monsoon rainfall, most surface runoff is lost before it can be captured and used productively. This study evaluated the potential of rainwater harvesting collecting and storing runoff through farm ponds and check dams to improve crop water availability across these two drought-prone districts through an integrated approach combining spatial suitability analysis, hydrological modelling, and scenario-based water balance evaluation. Suitable sites were identified using GIS-based spatial analysis of five biophysical criteria: rainfall, drainage density, slope, soil texture, and land use. Across the 4,581 km² study area, 2.5% of land was highly suitable and 43.4% moderately suitable, with the best locations concentrated in the flat lowlands of Bannu and the valley floors of Karak. Using 43 years of CHIRPS rainfall records with SCS-CN runoff modelling, 3,583 farm pond locations and 91 check dam sites were identified. Runoff reaching check dam catchments during a single major storm was 54 times greater than total proposed storage capacity, confirming that scarcity is one of infrastructure rather than rainfall.Crop irrigation demand was estimated following FAO-56 guidelines across 84,837 hectares of cropland, yielding an annual gross demand of 459 Mm³/year. Current supply from the Bannu Canal System and existing infrastructure meets only 50% of this demand. Four RWH design scenarios were evaluated by varying pond depth (2–5 m) and check dam buffer distance (400- 600 m), all receiving identical annual runoff inflow of 137.6 Mm³. The optimal configuration Scenario S2 (3 m depth, 400 m buffer) yielded the highest net usable storage of 61.4 Mm³/year, retaining 44.6% of annual inflow. S2 achieves 86% demand coverage in October and full coverage in Nov-Dec, delivering greatest benefit during the shoulder season when monsoon charged storage meets early Rabi crop establishment. June–July remains a critical gap period that RWH alone cannot resolve.The findings confirm that the water deficit in Karak and Bannu is fundamentally a storage problem rather than a rainfall limitation. Decentralized RWH can meaningfully supplement existing canal and groundwater supply during shoulder seasons but cannot replace centralized infrastructure for peak summer demand. This study provides spatial suitability maps, hydrological estimates, and scenario-based water balance outputs to support evidence-based water planning in drought-prone districts of Khyber Pakhtunkhwa. |
