Evaporation Controlled by Boundary Layer Feedbacks in an Irrigated Semi-Arid Environment: a LIAISE Modeling and Data Study
Authors: Mangan Mary Rose , Hartogensis Oscar , Vilà Guerau de Arellano Jordi 
Published: March 2022

&lt;p&gt;The LIAISE experiment (&lt;em&gt;L&lt;/em&gt;and surface &lt;em&gt;I&lt;/em&gt;nteractions with the &lt;em&gt;A&lt;/em&gt;tmosphere over the &lt;em&gt;I&lt;/em&gt;berian &lt;em&gt;S&lt;/em&gt;emi-arid &lt;em&gt;E&lt;/em&gt;nvironment) was conducted during the summer of 2021 in the Pla d&amp;#8217;Urgell region of the Ebro River Valley in Catalonia, Spain (Boone et al., 2021).&amp;#160; In the LIAISE experimental region, the surface was homogeneous at the field scale (e.g. fields of alfalfa); however, the surface was heterogeneous at the regional scale (~10-100km) because of the spatial distribution of irrigated crops and dry natural vegetation.&amp;#160; During the LIAISE experiment, there were extensive observations of both the surface and the boundary layer in the dry and irrigated landscapes.&amp;#160; The observed boundary layer is formed through a composite of surface fluxes from both the irrigated and rainfed surfaces.&amp;#160; Likewise, the observed surface fluxes of individual fields in both regions are controlled by both the surface properties and the regional boundary layer characteristics.&amp;#160;&lt;/p&gt;&lt;p&gt;In this study, we examine the impact of the boundary layer on surface fluxes at two of the LIAISE sites: one in the irrigated, crop-covered area and one in the dry, naturally-vegetated area. &amp;#160;We use an atmospheric mixed-layer column model (CLASS, Vil&amp;#224;-Guerau de Arellano et al., 2015) that is heavily constrained by the surface and boundary layer observations from the LIAISE experiment.&amp;#160; The modeling approach consists of two steps: first the boundary layer was modeled using a composite surface to mimic the landscape scale processes as a control, then a local perspective was adopted to investigate the drivers of evaporation in both the irrigated and rainfed areas.&amp;#160; At the local scale, we use a parameterized evaporation tendency equation introduced by van Heerwaarden et al., 2010 for both model data and observations.&amp;#160; This equation is used both to evaluate the time tendency of boundary layer feedbacks to evaporation and to diagnose the causes of local evaporation tendency. &amp;#160;This approach allows us to quantify the relative importance of the boundary layer controls on evaporation compared to other controls on evaporation (e.g. radiation and advection) at the field scale.&lt;/p&gt;&lt;p&gt;References&lt;/p&gt;&lt;p&gt;Boone, A., Bellvert, J., Best, M., Brooke, J., Canut-Rocafort, G., Cuxart, J., Hartogensis, O., Le Moigne, P., Mir&amp;#243;, J. R., Polcher, J., Price, J., Quintana Segu&amp;#237;, P., &amp; Wooster, M. (2021, December). Updates on the International Land Surface Interactions with the Atmosphere over the Iberian Semi-Arid Environment (LIAISE) Field Campaign. &lt;em&gt;GEWEX News&lt;/em&gt;, 17&amp;#8211;21.&lt;/p&gt;&lt;p&gt;van Heerwaarden, C. C., Vil&amp;#224;-Guerau de Arellano, J., Gounou, A., Guichard, F., &amp; Couvreux, F. (2010). Understanding the Daily Cycle of Evapotranspiration: A Method to Quantify the Influence of Forcings and Feedbacks. &lt;em&gt;Journal of Hydrometeorology&lt;/em&gt;, &lt;em&gt;11&lt;/em&gt;(6), 1405&amp;#8211;1422. https://doi.org/10.1175/2010JHM1272.1&lt;/p&gt;&lt;p&gt;Vil&amp;#224;-Guerau de Arellano, J., van Heerwaarden, C. C., van Stratum, B. J. H., &amp; van den Dries, K. (2015). &lt;em&gt;Atmospheric Boundary Layer: Integrating Chemistry and Land Interactions&lt;/em&gt;. Cambridge University Press.&lt;/p&gt;