A network of stations for long-term evapotranspiration monitoring using the Bowen ratio, eddy covariance, and scintillometer methods in the Czech Republic and Austria

Since 2008, a network of weather stations has been gradually built in the Czech Republic (9 sites) and Austria (5 sites) for monitoring evapotranspiration using the Bowen ratio and energy balance method (BREB, 16 units in total), eddy covariance (EC, 5 units), and scintillometers (4 units). The monitoring takes place over diverse agricultural surfaces, such as permanent grasslands, intensively managed arable land, and short-rotation woody coppices. The main focus is put on the seasonal monitoring of turbulent energy fluxes of sensible and latent heat flux, which is further processed as actual evapotranspiration, and usable for water balance analyses, drought monitoring, etc. At selected locations of interest, BREB measurements are combined with EC systems and scintillometers to allow cross-validation of different methods and mutual comparisons as BREB and EC methods determine fluxes within a footprint centered around point measurement in the middle of the field, whereas scintillometer provides an estimation of sensible heat flux integrated over the measurement path length, which is particularly useful in conjunction with remote-sensing products having a coarser resolution, than point measurements. Last but not least, the network serves as a test bed for the development and testing of new approaches to measuring evapotranspiration, i.e. surface renewal/flux variance method. The network is also used to support the Czech drought monitoring system (see www.interdrought.cz) as well as an independent tool for point validation. Due to the long-span dataset gathered, instances of several drought events from selected sites will be presented and analyzed, with the main focus on seasonal actual evapotranspiration during the dry years 2015-2018 at different sites.