09 Feb 2023
 | 09 Feb 2023
Status: this preprint is currently under review for the journal HESS.

On the importance of phenology in the evaporative process of the Miombo Woodland: Could it be why satellite-based evaporation estimates differ?

Henry Zimba, Miriam Coenders-Gerrits, Kawawa Banda, Petra Hulsman, Nick van de Giesen, Imasiku Nyambe, and Hubert H. G. Savenije

Abstract. Complex African ecosystems such as the Miombo Woodland, with unique plant phenology, have evaporation dynamics that have not been investigated due to very few, if at all existant, flux tower observations. Furthermore, significant differences have been observed in satellite-based evaporation estimates in the Miombo Woodland especially in the dry season. Therefore, deciding which sattelite evaporation product to use in this ecosystem is difficult, as these products vary in many respects. In this study, the actual evaporation estimates for six satellite-based evaporation estimates are compared across Miombo Woodland phenophases in the Luangwa Basin, in southern Africa. In the absence of basin scale field observations, the actual evaporation estimated using the general water balance is used as reference, to which the six satellite-based evaporation estimates have been compared. Our results show significant variation in actual evaporation estimates in the water limited, high temperature and lower forest canopy cover and leaf chlorophyll conditions in the dormant phenophase. Lowest variation is observed in water abundant, high temperature, high leaf chlorophyll content and high forest canopy cover in the maturity/peak phenophase(s). Compared to the basin scale water balance actual evaporation, all six satellite-based evaporation estimates appear to underestimate evaporation. The results of underestimation at basin scale agrees with local field observations in a dense Miombo Woodland in the Luangwa Basin, which indicates that satellite-based evaporation estimates generally underestimate dry season (dormant phenophase) and early rain season (green-up phenophase) actual evaporation. The discrepancies in dry season satellite-based evaporation estimates may be cuased by the Miombo Woodland species’ phenological adaptation attributes such as: leaf fall, leaf flush, access to deep soil moisture and the within vegetation water storage, coupled with heterogenous plant species response to phenological stimuli. Therefore, it appears that satellite-based evaporation estimates using model structure, processes and inputs that are capable of capturing Miombo species dry season phenological interaction with climate are likely to have actual evaporation estimates closer to field conditions.

Henry Zimba et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on hess-2023-39', Graham Jewitt, 17 Mar 2023
    • AC2: 'Reply on RC1', Henry Musonda Zimba, 30 Apr 2023
    • AC3: 'Reply on RC1', Henry Musonda Zimba, 30 Apr 2023
  • RC2: 'Comment on hess-2023-39', Anonymous Referee #2, 24 Mar 2023
    • AC1: 'Reply on RC2', Henry Musonda Zimba, 29 Apr 2023

Henry Zimba et al.

Henry Zimba et al.


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Short summary
In the dry season some Miombo plant species may have no leaves while several others are full of leaves and have access to water in deep soils and within the plants. Therefore, the plants continue to lose water to the atmosphere as they interact with the available energy and water. All the six satellite-based evaporation estimates compared in this study underestimates this plant water loss because they appear to have difficulties capturing the unique dry season Miombo plants attributes.