Int. J. Global Warming, Vol. 14, No. 3, 2018 313 Copyright © 2018 Inderscience Enterprises Ltd. Nonparametric trend analysis of reference evapotranspiration for Khyber Pakhtunkhwa, Pakistan Sajid Gul, Ijaz Hussain* and Muhammad Yousaf Shad Department of Statistics, Quaid-i-Azam University, 44000 Islamabad, Pakistan Email: sgqaustat@gmail.com Email: ijaz@qau.edu.pk Email: yousuf@qau.edu.pk *Corresponding author Muhammad Faisal Faculty of Health Studies, University of Bradford, BD7 1DP Bradford, UK and Bradford Institute for Health Research, Bradford Teaching Hospitals NHS Foundation Trust, Bradford, UK Email: mfaisal@qau.edu.pk Alaa Mohamd Shoukry Arriyadh Community College, King Saud University, Riyadh, Saudi Arabia and King Saud University, KSA Workers University, Egypt Email: aabdulhamid@ksu.edu.sa Shahzada Adnan Department of Meteorology, COMSATS Institute of Information Technology (CIIT), Islamabad Campus, Pakistan and National Drought Monitoring Centre, Pakistan Meteorological Department, Pitras Bukhari Road, 44000 Islamabad, Pakistan Email: shaz.adnan@gmail.com