Comment on egusphere-2023-375

Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> The lateral transport of water in the subsurface is important in modulating the terrestrial water-energy distribution. Although few land surface models have recently included lateral saturated flow within and across grid cells, it is not a default configuration in the Climate Model Intercomparison Project version 6 experiments. In this work, we developed the lateral subsurface flow model with both unsaturated and saturated zones in the Energy Exascale Earth System Model (E3SM) Land Model version 2 (ELMv2.0). The new model, called ELM_<em>lat</em>, was benchmarked against PFLOTRAN, a 3D subsurface flow and transport model, for three idealized hillslopes that included a convergent hillslope, divergent hillslope, and titled V-shape hillslope with variably saturated initial conditions. ELM_<em>lat</em> showed comparable performance with PFLOTRAN in terms of capturing the dynamics of soil moisture and groundwater table for the three benchmark hillslope problems. Specifically, the mean absolute errors (MAE) of the soil moisture in the top five layers between ELM_<em>lat</em> and PFLOTRAN were within 1 % &plusmn; 4 % and the MAE of water table depth were within &plusmn; 0.3 m. Next ELM_lat was applied to the Little Washita experimental watershed to assess its prediction of groundwater table, soil moisture, and soil temperature. The spatial pattern of simulated groundwater table depth agreed well with the global groundwater table benchmark dataset generated from a global model calibrated with long term observations. The effects of lateral groundwater flow on the energy flux partitioning were more prominent in low land areas with shallower groundwater tables, which the difference of simulated annual surface soil temperature could reach 0.4&ndash;0.5 &deg;C at low land areas between ELMv2.0 and ELM_<em>lat</em>. Incorporating lateral subsurface flow in ELM improves the representation of the subsurface hydrology which will provide a good basis for future large-scale applications.