Title: Nonparametric trend analysis of reference evapotranspiration for Khyber Pakhtunkhwa, Pakistan

Authors: Sajid Gul; Ijaz Hussain; Muhammad Yousaf Shad; Muhammad Faisal; Alaa Mohamd Shoukry; Shahzada Adnan

Addresses: Department of Statistics, Quaid-i-Azam University, 44000 Islamabad, Pakistan ' Department of Statistics, Quaid-i-Azam University, 44000 Islamabad, Pakistan ' Department of Statistics, Quaid-i-Azam University, 44000 Islamabad, Pakistan ' Faculty of Health Studies, University of Bradford, BD7 1DP Bradford, UK; Bradford Institute for Health Research, Bradford Teaching Hospitals NHS Foundation Trust, Bradford, UK ' Arriyadh Community College, King Saud University, Riyadh, Saudi Arabia; King Saud University, KSA Workers University, Egypt ' Department of Meteorology, COMSATS Institute of Information Technology (CIIT), Islamabad Campus, Pakistan; National Drought Monitoring Centre, Pakistan Meteorological Department, Pitras Bukhari Road, 44000 Islamabad, Pakistan

Abstract: Reference evapotranspiration (ET_o) is a key element of the hydrological cycle that integrates atmosphere demand and surface environment conditions. In this study, we aimed to determine the trend of ET_o using nonparametric methods - Mann-Kendall and Sen's slope estimator, whereas ET_o is estimated using globally accepted Food and Agriculture Organization (FAO) Penman-Montieth FAO-56 (PM) method. We used ten years data (2000-2009) of 11 weather stations located in Khyber Pakhtunkhwa Province, Pakistan. We identified a decreasing trend in ET_o rate has been recorded mostly in winter, pre-monsoon and spring with an upward trend during autumn and red-summer. Further, the statistical analysis shows a significant decreasing trend in ET_o during winter. In summary, we provide a systematic approach that may be used in agro meteorological modelling and irrigation development.

Keywords: evapotranspiration; FAO-56 PM; trend analysis; Mann-Kendall; Sen's slope estimator; season; Pakistan.

DOI: 10.1504/IJGW.2018.090399

International Journal of Global Warming, 2018 Vol.14 No.3, pp.313 - 329

Received: 03 Dec 2015
Accepted: 29 Aug 2016
Published online: 14 Mar 2018 *

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