10 Oct 2022
10 Oct 2022
Status: this preprint is currently under review for the journal HESS.

Measuring evaporation across canopy phenophases of a natural forest: Miombo forest, Southern Africa

Henry Zimba1,2, Miriam A. J. Coenders-Gerrits1, Kawawa E. Banda3, Bart Schilperoort1, Imasiku A. Nyambe3, Nick C. van de Giesen1, and Hubert H. G. Savenije1 Henry Zimba et al.
  • 1Delft University of Technology, Water Resources Section, Building 23 (Faculty of Civil Engineering and Geosciences) 2628 CN Delft, P.O Box 5048 2600 GA Delft, The Netherlands
  • 2Ministry of Agriculture, Department of Agriculture, P.O Box 50595, Mulungushi House, Independence Avenue, Lusaka, Zambia
  • 3University of Zambia, Integrated Water Resources Management Centre, Department of Geology, School of Mines, Great East Road Campus, Lusaka, Zambia

Abstract. Atmospheric water demand drives forest evaporation controlled by the plant physiological properties within available moisture storage thresholds. The pattern and magnitude of African Miombo Forest transpiration across dry season canopy phenophases are unknown. This is because estimating forest evaporation in African ecosystems continues to be a challenge as flux observation towers are scant, if not completely lacking in most ecosystems like the Miombo Forest, one of Africa’s largest woodland formations. Moreover, in the Miombo Forest, satellite data-based evaporation products (i.e., GLEAM, MOD16, SSEBop and WaPOR) show significant discrepancies in both pattern and amounts of evaporation especially during the dry season canopy phenophases. Despite the main limitations with estimation of forest evaporation the development and application of the distributed temperature sensing (DTS) system is providing deepened insights and improved accuracy in forest energy partitioning for evaporation assessment. In this study the Bowen ratio distributed temperature sensing (BR-DTS) approach is used to partition available energy and estimate evaporation across three Miombo Forest canopy phenophases covering the entire 2021 dry season and early rain season. Furthermore, four satellite evaporation products are compared to the field observations. Results show that evaporation appears to follow the net radiation and air temperature pattern with the lowest values observed during the most net radiation and air temperature depressed periods and highest values during the peak net radiation and air temperature. Evaporation continues to rise even during the driest period in the dormant leaf phenophase when canopy cover is said to be at its minimum. This is possibly facilitated by the retention of about 70 percent canopy cover during the dry season which transpires within the adapted thresholds constrained by physiological properties of each Miombo Forest species with access to ground water and vegetative water storage. This goes to show that during the dry season Miombo species may not be as water stressed as imagined. When compared to field observations all four-satellite evaporation products underestimate evaporation with only the WaPOR showing a similar pattern of evaporation during the dry season. The differences between field observations and satellite-based evaporation products can be attributed to the model structure, processes as well as inputs.

Henry Zimba et al.

Status: open (until 05 Dec 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on hess-2022-303', Anonymous Referee #1, 08 Nov 2022 reply
  • RC2: 'Comment on hess-2022-303', Anonymous Referee #2, 10 Nov 2022 reply

Henry Zimba et al.

Data sets

ZAMSECUR Project Miombo Forest, Zambia, Southern Africa Henry Zimba, Hubert H.G. Savenije, Nick van de Giesen, Miriam CoendersMiriam Coenders, Bart Schilperoort

Henry Zimba et al.


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Short summary
Miombo Forest plants continue to lose water even during the driest part of the year. This appears to prove developed water loss control system that accounts for access to ground water and the water the plant is able to store within itself. It appears the changes in air temperature and solar radiation is what largely influences the pattern and amount of water that the plants lose. This dry season behaviour of Miombo Forest plants is not correctly captured by most of the satellite based models.