Evapotranspiration at four sites representing land-use and height gradient in the Eastern Ore Mountains (Germany)

Abstract. Less is known about evapotranspiration (ET) along elevation gradients of low mountain ranges, especially with regard to different land uses and concerning long-term studies. We investigate ET of four sites of different land-uses along an elevation gradient of a low mountain range over eleven years (2008–2018) based on daily values. Three different ET estimates are inspected, which can give a reasonable range of ET. These estimates are ET based on the energy balance residual (ET_residual), ET corrected for the energy balance closure gap (ET_corr) and ET not corrected for the energy balance closure gap (ET_uncorr). In general, ET_residual showed largest values and ET_uncorr showed lowest values with ET_corr in between. Average annual differences between ET_residual and ET_corr ranged between 111 mm a⁻¹ and 196 mm a⁻¹. Average annual differences between ET_uncorr and ET_corr ranged between 70 mm a⁻¹ and 167 mm a⁻¹. For two site years ET_corr was lower than ET_uncorr. This could be related to gap-filling. Differences between different estimates were site-specific and related to the respective energy balance closure gap. Principal component analysis revealed similar dependency on driving variables for all three estimates and all sites. Given the influence of the energy balance closure gap on ET_uncorr and ET_residual, we recommend using ET_corr, but ET_residual can be still useful especially for sites with low vegetation, which rarely experience water stress. Comparison of two coniferous sites situated at different altitudes showed frequently larger values for the site located at a higher altitude. This might be a result of rainfall interception, which however must be investigated at sub-daily timescale.