On the importance of phenology in the Miombo ecosystem: Evaluation of open-source satellite evaporation models
Abstract. Accurate spatial-temporal information on evaporation is needed for use in many sectors including hydrology, agriculture and climate studies. This would require a dense observation network, which is practically impossible. Over the past decades, remotely sensed evaporation models to estimate spatially continuous evaporation have been developed. However, deciding which model to use is a challenge as these models vary in complexity and accuracy across the different global ecosystems. It is even more challenging for complex African ecosystems that have very few, or none at all, flux tower observations. In this study, we used the general water balance evaporation (Ewb) as reference to which we compared six models that determine evaporation, i.e., FLEX – TopoWB, TerraClimate (TMCWB), GLEAM, MOD16, SSEBop and WaPOR, in the Luangwa Basin, a semi-arid catchment in the Miombo ecosystem in southern Africa. FLEX – TopoWB and TMCWB models are calibrated on discharge, while GLEAM, MOD16, SSEBop and WaPOR have been validated on evaporation data from flux tower observations. Key focus is on inter-model performance comparison in the Miombo ecosystem across phenophases and land cover types. Results show that major spatial-temporal discrepancies in model performance occur in the forest and open water body land surfaces during the dormant and green-up phenophases in the dry season. Compared to Ewb, annually WaPOR consistently overestimated evaporation while GLEAM consistently underestimated evaporation. The rest of the models showed biases within the GLEAM and WaPOR boundaries. With reference to bias, SSEBop and WaPOR showed lowest aggregated 2009–2020 bias in terms of estimating long-term average annual evaporation. It appears that correct understanding of the Miombo vegetation phenology associated moisture feedbacks and incorporating these in model structure is likely to improve evaporation estimates in the Luangwa Basin and Miombo Woodland ecosystem as a whole.
