Climate Change Adjustment Factor on rainfall depths in river basins of Khyber Pakhtunkhwa, Pakistan

Abstract Flooding in Pakistan is generally contributed from rivers and floods are generally caused by heavy concentrated rainfall in the river basins during the monsoon season (July through September). Pakistan has a long history of floods and associated damages. Due to global climate change and its impact on Pakistan in recent years, the frequency and intensities of floods and corresponding damages have increased manifold. In the recent history, Pakistan has experienced unprecedented flooding in Khyber Pakhtunkhwa (KPK) in 2010 and 2022; occurrence of the flood events in upper most reaches of northern areas have proved that the climate change has severely impacted our region. In this study, 20 CMIP-6 General Circulation Models (GCMs) have been selected for the individual river basins of KPK namely Swat, Panjkora, Chitral, Kabul, Kurrum, Gomal and DI Khan. These models have undergone qualitative evaluations to determine their suitability for further analysis. The scrutiny of model selections is based on specific criteria, including daily frequency of data, availability of SSP 2-4.5 (middle of the road) and SSP 5-8.5 (business as usual) scenarios, and correlations between observed and climate model data, which helps exclude the least reliable GCMs. Based on the criteria, daily data for both baseline and future scenarios have been downloaded and processed for 20 GCMs that passed the initial evaluation. Subsequently, these shortlisted GCMs underwent additional assessments for dry, wet, hot, and cold conditions (delta approach method). As a result, five GCMs in each catchment have been selected as the most suitable candidates for conducting future climate projections. Statistical downscaling technique was opted for and corrected precipitation data from Quantile Delta Mapping (QDM) approach. To estimate the return period of maximum daily precipitation, the widely used Generalized Extreme Value (GEV) distribution was employed. Results indicates an adjustment factor for design rainfall under a 100-year return period in KPK, Pakistan, range from 1.2–21.3% due to climate change, also factors have been calculated for various return periods in study. This study offers valuable insights for engineers, planners, and various departments to the rising risk of extreme rainfall and to flooding. Understanding these impacts is crucial for developing effective adaptation strategies to mitigate the effects of climate change in the region.