Evaluation of pan coefficient for reference crop evapotranspiration for Igdir region of Turkey

Abstract

Pan coefficient (Kpan) is the important factor to convert from pan evaporation (Epan) to reference evapotranspiration (ETo). There are several methods to estimate Kpan, but their performance in different environments is diverse. In this study, approaches proposed by Cuenca (1989), Snyder (1992), Orang (1998), Allen and Pruitt (1991), Raghuwanshi and Wallender (1998), and Pereira et al. (1995) were evaluated by comparing them with the FAO 56 Penman-Monteith (FAO-PM) method. For this study, weather data sets collected during the growing seasons of 2004 and 2008 in the Igdir region of Turkey were used. The monthly analysis showed that the Allen and Pruitt (1991) equation provided the best agreement with the FAO 24. The weekly, 10-day and monthly analysis indicated that the Snyder (1992) equation showed better agreement than other Kpan equations with the FAOPM method, followed by equations of Cuenca (1989), Allen and Pruitt (1991) and Orang (1998). The results suggested that, under the Igdir conditions, the ETo data from these four equations using weekly or more long-term averages of daily meteorological data could easily be used for irrigation scheduling.