Evapotranspiration and crop coefficient of common reed at the surroundings of Lake Balaton, Hungary

• Six-season mean of measured evapotranspiration (ET) for common reed was 774 mm in Hungary.
• Actual weather, mainly air temperatures influenced strongly the reed ET (based on AIC).
• Reference ET (FAO 56) was on average 70% of the locally measured ET.
• Monthly Kc ranged from 0.6 to 1.62 with an average of 1.23 for the whole study period.

This study analysed the variation in the crop coefficient (Kc)of local common reed (Phragmites australis) stands based on evapotranspiration (ET) and local reference (Penman–Monteith) ET measurements at the surroundings of Lake Balaton, Hungary. ET was measured daily over several seasons with modified Thornthwaite-Matter evapotranspirometers with compensative irrigation using free-flowing above-ground water. This modified irrigation regime enabled the long-term cultivation of common reed. The average annual water loss of common reed of six seasons between 2005 and 2011 ranged from 566 to 1008 mm but depended on the weather, especially on net radiation. The average ET of common reed was 779 mm for the entire study period while the average Kc value was 1.23. Seasonal mean Kc values for common reed ranged from 0.73 to 1.37. In cool weather (seasonal mean air temperatures <17 °C), annual mean Kc and ET were 0.73 and 385 mm, respectively while in hot weather (seasonal mean temperatures above 18 °C), Kc and ET were 1.37 and 875.4 mm, respectively. Multiple regression analysis and Akaike Information Criterion were used to determine the relationship between ET and different meteorological variables, and indicated that the leading factors were the air temperatures and net radiation on ET during the study. In the common reed community, the driving force on ET was the available energy.These observations, which cover a six-year period, may be more valid and reliable than other measurements made in the literature thus far, all of which reported a shorter observation period.