On the multi-scale analysis of land-surface mass and energy exchanges for the tropical Andean páramo of Southern Ecuador
Studies on the atmosphere-surface exchange processes over montane regions represent a growing field. This is particular on the scope of ecohydrological investigations, which assess the estimation and prediction of water, carbon and energy fluxes, among other functional key-indicators of the biomes....
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|Studies on the atmosphere-surface exchange processes over montane regions represent a growing field. This is particular on the scope of ecohydrological investigations, which assess the estimation and prediction of water, carbon and energy fluxes, among other functional key-indicators of the biomes. Therefore, the understanding of the complexity of energy-driven processes such as actual evapotranspiration (ETa) and carbon dioxide (CO2) exchange is fundamental, particularly for the biodiverse tropical highlands, which are exposed to human-induced treats (e.g., global warming and land cover change). Herein, the Andean páramo region of Ecuador (3200-5000 m a.s.l.) supports vital ecosystem services, such as water supply, carbon storage and biodiversity. This biome is crucially important for the sustainability of the inter-Andean valleys’ inhabitants, mainly due to its role as a massive water reservoir. Atmosphere-surface exchange processes in the páramo are largely unknown.
The aim of this thesis is to analyze the water, energy and carbon flux transfer mechanisms in páramo catchments of Southern Ecuador, by a multi-scale approach, which considers point-scale (ecosystem) and spatial-scale (catchment), through ground-level (instrumental-based) and remote sensing level (model-based). This methodology allows to quantify the accuracy of each technique, and to identify the most appropriate method according to site characteristics. This work has contemplated: (i) The analysis of the spatial dynamics of ETa derived from satellite products (Landsat and MODIS) with a calibrated energy balance-based model (METRIC), and the evaluation with a global ETa product (MOD16) and with ETa obtained as water balance residual (WB); (ii) the detection and analysis of ground-level and ecosystem-scale ETa, energy and CO2 fluxes (through eddy covariance (EC) and micrometeorological methods), their interaction with environmental controls, and the comparison of EC ETa with widely applied reference ET models (ETr); and finally, (iii) the evaluation of simulated ETa and energy fluxes obtained from a state-of-art land-surface model (CLM) parameterized to the biophysical and climate conditions of two páramo catchments. The CLM outcomes evaluation was performed with METRIC ETa, energy fluxes observations (EC) and with WB-derived ETa.
The findings of the first analysis reveal that spatial ETa can be successfully estimated when a proper calibration of the model parameters and a high resolution satellite product is used simultaneously. The ETa temporal dynamics from this approach showed consistent results with WB ETa. The results of the second part, demonstrate the plausibility of EC for gas and energy flux detection on this mountain ecosystem. The CO2 budget (at different time scales) reveals the ‒carbon source‒ behavior of the páramo, which constitutes an outstanding discovery in the knowledge about this region. Mathematical functions between carbon fluxes and biophysical controls (available light and soil temperature) are also reported. The quantification of water loss in the form of ETa, and its comparison with modeled ETr, allowed for the first time, to report truthful crop coefficients for the páramo grasslands. Finally, the third analysis revealed the plausibility of CLM for ETa prediction, in spite of a poor performance of the model for the simulation of specific energy fluxes (net radiation, sensible and soil heat). The evaluation between methods, also demonstrated that METRIC ETa values are closer to the EC ETa observations, and revealed that WB ETa rendered poorly. These analyses provide insights on the methods’ selection for future studies in similar locations.
The current investigation provides solid answers to unsolved questions about the dynamics of the ETa, CO2 and energy fluxes of the páramo, and the multiscale approach adopted enhance our understanding of the ecohydrological processes of this unique Andean ecosystem.