Spatial and temporal variation of three Eddy-Covariance flux footprints in a Tropical Dry Forest

Tropical Dry Forest (TDF) is a distinctive ecosystem characterized by distinct seasonal changes, primarily composed of deciduous trees adapted to endure prolonged drought periods. Obtaining ecosystem-scale flux measurements using the Eddy Covariance (EC) technique is crucial for comprehending the spatiotemporal dy-namics of interactions between the land and the atmosphere. It is imperative to have information about the variability in the contribution source area of the Flux Footprint Area (FFA) to assess the impact of changing microclimate variables on the EC FFA. In this study, we describe and evaluate the influence of various phases of the El Nino Southern Oscillation (ENSO) on the spatial and temporal climatology of FFA at three EC sites within the TDF of the Santa Rosa National Park-Environmental Super Site (SRNP-EMSS). Our analysis covered the period from 2014 to 2021 on a seasonal scale and employed a 2D model. Our findings indicate that: a) seasonal climatology FFAs exhibit variation across locations and over time due to factors such as forest canopy height, site topography, wind direction, and atmospheric stability conditions; b) FFAs are smaller during dry seasons compared to wet seasons; and c) multiple ENSO phases (cold, neutral, and warm) significantly affect the seasonal climatology of FFAs. Notably, during the moderate La Nina phase (2020/2021), the mean FFA size was 4.20 km(2), which was 23.80% larger than the mean FFA during the intense El Nino phase (2015/2016) at 3.20 km(2). Additionally, during La Nina phases, FFAs were more asymmetrically distributed around the EC tower compared to El Nino phases, with mean symmetric indices of 0.35 and 0.29, respectively. Finally, the overlap among the three EC climatology FFAs during La Nina phases was 35% greater than that during the El Nino phases. Our study highlights how variations in FFAs can significantly impact intra-annual flux estimates.