A long-term (2012-2021) measurement and modelling evapotranspiration of the Biebrza Valley wetland area (Poland)

The primary goal of the study is to characterize the evapotranspiration of wetlands against the background of changing meteorological conditions. The relatively long measurement period makes it possible to show the dynamics of this process both under conditions of high precipitation and periods of drought. Moreover, the analyzed period also includes measurements of evapotranspiration under conditions of rapid recovery of wetland vegetation after fire. The accomplishment of the research objectives was based on measurements using the eddy covariance method in the Biebrza National Park in northeastern Poland. The measurement period covers the years 2013–2021. Latent heat flux Qe is characterized by a distinct annual cycle with the highest values in the summer season. Average daily values of Qe from July to August were in the range of 6–10 MJ m ^− 2 d ^− 1 , which is on average 60–70% of the value of the radiation balance. The relatively long measurement period showed that the evapotranspiration of the wetland surface is characterized by very high stability. The achieved values of daily as well as monthly totals during periods of drought were very close to those recorded in seasons with high precipitation. The high rate of evapotranspiration led to a decrease in groundwater levels and a significant deterioration in the water resources of the wetland environment.