A reference evapotranspiration map for Bosnia and Herzegovina

Abstract

There are three major challenges for climatic data availability for Reference Evapotranspiration (ET0) calculations in Bosnia and Herzegovina: limited data availability, discontinuity of data records, and low station density. The main objective of this study was to apply reliable methods to calculate and spatially distribute ET0, while considering the impact of the elevation. A 20 m spatial resolution map was created for mean ET0 values at monthly, vegetation period (April–September) and annual temporal resolution at municipality (143 municipalities), regional (4 regions) and national spatial resolutions. 108 weather stations for the period 1961–2016 (56 years) were utilized for spatial interpolation of ET0 using kriging with external drift method. The required elevation for ET0 estimation at each grid node was extracted from the digital elevation model of Bosnia and Herzegovina. ET0 was calculated using FAO-56 Penman-Monteith, and in cases where only minimum and maximum temperature data were available the Hargreaves-Samani equation adjusted with locally appropriate empirical radiation coefficient was used. A gradual decrease of mean ET0 values from the southern to central and northern to central part of the country is notable. For the all seasons (monthly, vegetation and annually), the southern region has greater ET0 than the other three regions (north, west and central-east), which are similar. The long-term mean annual ET0 for Bosnia and Herzegovina is 716 mm, approximately 78% (559 mm) of which occurs during in the vegetation period. Keywords: Reference evapotranspiration, Interpolation, Penman-Monteith, Limited data, Calibration