## 1 Introduction  
In the central and southeastern United States, deciduous forested wetlands located in broad floodplain areas bordering large river systems such as within the Lower Mississippi Alluvial Valley (LMAV) are referred to as Bottomland Hardwood Forests (BHFs) [1]. Many ecosystem services provided by BHFs, including water quality regulation, flood control, wildlife habitat, timber production, waste treatment and disturbance regulation, and climate moderation through carbon balance are of global importance [2, 3]. Like other wetland types, a hydrological regime of alternating wet and dry cycles driven by fluctuating water levels of the associated rivers and groundwater level changes is characteristic of BHFs [4, 5]. The sustainability of BHFs depends primarily on the longitudinal (upstream to downstream), lateral (river to floodplain to uplands and vice versa), vertical (surface water to groundwater and vice versa), and temporal (seasonal and annual flooding) variability of water availability [6]. The primary force controlling the biota in BHFs is the flooding pulse from adjacent water sources, which deposits dissolved nutrients, organic matter, and sediment, also contributing to the formation of young floodplains with each flooding pulse [7]. Even small changes in the duration and frequency of water levels can result in a distinct shift in the plant community, as many species are adapted to a certain range of flood tolerance [8]. Therefore, a deeper understanding of the water use pattern and surface energy balance in these BHFs is crucial to preserving this dwindling ecosystem along the LMAV. The study of BHF ecology remains incomplete without the assessment of factors that are integral to the proper functioning of these systems--evapotranspirationiration (ET), flood regimes, and precipitation. ET has been reported as a major component of BHFs' water balance in several studies, along with LE (heat energy equivalent to ET) dominating the surface heat balance [9; 10]. Several previous studies have identified biological and climatic drivers of bottomland hardwood ET using chronosequence analyses [9], sap-flux measurements [11], and statistical modeling approaches [12] in the southeastern US. These studies report a strong correlation between net radiation (R\({}_{\text{n}}\)), temperature, and other climatic conditions consistent with the site specificities and variations in ET during different seasonal cycles. The Vapor Pressure Deficit (VPD) has been established as one of the primary drivers of ET and is used increasingly in global simulation studies [13]. For example, [14] used maximum likelihood estimation methods to show a complex chain of correlations among ET, VPD, radiation, and temperature in northern high-latitude woodland ecosystems. The complex interrelationships among these atmospheric variables, which are essential for an assessment of the ultimate drivers of variations in ET, can be explored using structural equation modeling (SEM). The use of SEM approaches to diagnose the independent contributions of atmospheric drivers in determining the ET variability from the BHFs largely remains unexplored. The complexity of interrelationships among multiple variables and their dependencies makes it challenging to quantify the actual contributions of the drivers of ET. SEM, a multivariate statistical modeling technique with factor analysis and path analysis, provides a framework to quantitatively evaluate these interrelationships that need to be untangled to characterize the role and independent contribution of each driver of the variations observed in ET. An SEM analysis carried out with the data measured at multi-site high-latitude regions showed that radiation, temperature, windspeed, and relative humidity (RH) loaded heavily on the first factor during the warm season (May-September) [15; 16].