UAV-based Studies of Temperature and Wind in and above a Deciduous Forest (and a Forest Clearing) in the Region of the Weser Valley
- 1Ostwestfalen-Lippe University of Applied Sciences, Environmental Engineering and Computer Sciences, Hoexter, Germany (burkhard.wrenger@th-owl.de)
- 2University of the Balearic Islands, Palma, Majorca, Spain (joan.cuxart@uib.cat)
Between the German cities of Höxter and Holzminden, the landscape ascends in the eastern direction from the Weser river at roughly 100 m a.s.l. up to 500 m a.s.l. in the Solling natural area. The slope is forested with deciduous trees with a typical height of approx. 30 m. In order to study the vertical profiles of temperature and wind in the forest, we operated an Unmanned Aerial Vehicle (UAV) flying from ground level up to approx. 100 m agl. Fifteen flights near sunset between summer 2019 and spring 2020 are analysed revealing effects of the foliation and downslope flows. Using rough estimates of turbulent fluxes and sensible heat and momentum based on the vertical profiles allows us to produce leaf area density profiles for the leafy and the leafless case. We compare the results with existing theories both for the average structure of the forest and the vertical profiles.
For the cases studied here, the forest exerts a drag on the wind and the wind decreases markedly in a 30-m-layer above the canopy. The drag is maximal at the upper canopy and the presence of the leaves increases this effect. Due to the slope situation, downslope flows can be detected and enhance the mixing near the surface. Based on the work by Yi [1] we can split the wind speed into contributions from the forest and the slope.
The estimation of turbulent fluxes is rough due to the limited data sample during the flights, but it is in agreement with the profiles of the mean variables. The momentum fluxes as a function of height allows the estimation of the profile of leaf area density as a fingerprint of the average structure of the forest. The results show that for a two storeys forest as present in the our region of interest, assuming a logarithmic profile of the variables does not reflect the measurements.
[1] C. Yi, R. K. Monson, Z. Zhai, D. E. Anderson, B. G. Allwine, A. A. Turnipsseed, S. T. Burns: Modeling and measuring the nocturnal drainage flow in a high-elevation, subalpine forest with complex terrain. Journal of Geophysical Researcj, Vol. 110, D22303 (2005)
How to cite: Wrenger, B. and Cuxart, J.: UAV-based Studies of Temperature and Wind in and above a Deciduous Forest (and a Forest Clearing) in the Region of the Weser Valley, EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-992, https://doi.org/10.5194/ems2024-992, 2024.
