hydrology Article Simplified Interception/Evaporation Model Giorgio Baiamonte   Citation: Baiamonte, G. Simplified Interception/Evaporation Model. Hydrology 2021, 8, 99. https:// doi.org/10.3390/hydrology8030099 Academic Editors: Aristoteles Tegos and Nikolaos Malamos Received: 6 June 2021 Accepted: 30 June 2021 Published: 2 July 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the author. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Department of Agricultural, Food and Forest Sciences (SAAF), University of Palermo, Viale delle Scienze, 90128 Palermo, Italy; giorgio.baiamonte@unipa.it Abstract: It is known that at the event scale, evaporation losses of rainfall intercepted by canopy are a few millimeters, which is often not much in comparison to other stocks in the water balance. Nevertheless, at yearly scale, the number of times that the canopy is filled by rainfall and then depleted can be so large that the interception flux may become an important fraction of rainfall. Many accurate interception models and models that describe evaporation by wet canopy have been proposed. However, they often require parameters that are difficult to obtain, especially for large-scale applications. In this paper, a simplified interception/evaporation model is proposed, which considers a modified Merrian model to compute interception during wet spells, and a simple power-law equation to model evaporation by wet canopy during dry spells. Thus, the model can be applied for continuous simulation, according to the sub hourly rainfall data that is appropriate to study both processes. It is shown that the Merrian model can be derived according to a simple linear storage model, also accounting for the antecedent intercepted stored volume, which is useful to consider for the suggested simplified approach. For faba bean cover crop, an application of the suggested procedure, providing reasonable results, is performed and discussed. Keywords: interception; linear storage model; evaporation; cover crop; water balance; faba bean 1. Introduction According to Brutsaert [1], the interception process is determined by the rainfall fraction that moistens vegetation and that is temporarily stored on it, before evaporating. When the vegetation cover is fully saturated, the interception storage capacity is achieved. In practice, the interception storage capacity is denoted as rainfall left on the canopy at the end of the rainfall after all drip has ceased [2]. The water stored on the canopy may evaporate soon after, thus short-circuiting the hydrologic cycle. Although most surfaces can store only a few millimeters of rainfall, which is often not much in comparison to other stocks in the water balance, interception is generally a signifi- cant process and its impact becomes evident at longer time scales [3]. Thus, interception storage is generally small, but the number of times that the storage is filled and depleted can be so large that the evaporation losses by wet canopy may become of the same order of magnitude as the transpiration flux [4]. Evaporation flux by canopy exerts a negative effect on plant water consumption by preventing water from reaching the soil surface, thus the plant roots [2,3]. In contrast, the remaining rainfall (i.e., the net rainfall) reaches the soil surface either as throughfall or by flowing down branches and stems as stemflow. Throughfall is the fraction of water that reaches the soil surface directly through the canopy gaps without hitting the canopy surfaces, or indirectly through dripping from the leaves and branches [5]. The interception may also exert important effects on surface runoff [6], providing a certain delay compared with the time of the beginning of the rain. For the Dunnian mech- anism of runoff generation, Baiamonte [7] showed the effect induced by the interception process on the delay time, and emphasized that the effect is more frequent for well-drained soils [8,9] in humid regions, for low rainfall intensities and high groundwater table, when infiltration capacity exceeds the rainfall intensity. Indeed, the latter conditions also occurs Hydrology 2021, 8, 99. https://doi.org/10.3390/hydrology8030099 https://www.mdpi.com/journal/hydrology