Emergent surface water dynamics across wetlandscapes in the NOAA GFDL Land Model

Wetlands play a critical role in regulating hydrologic, energetic, and biogeochemical processes across landscapes. Yet Earth System Models (ESMs) remain unable to represent one of their defining physical features: shallow surface-water ponding. Because most land models describe wetness only through soil moisture or water-table depth, they cannot simulate the temporary storage, lateral redistribution, and seasonal expansion of surface water that can affect evapotranspiration, surface energy partitioning, and greenhouse-gas exchange. This limitation weakens our ability to represent how wetlands embedded within larger wetlandscapes regulate water, climate, and carbon fluxes.

We have recently developed a new Surface–Soil Exchange and Emergent Ponding (SEEP) scheme within the NOAA GFDL land model (LM4.1). SEEP introduces an explicit surface water column, two-way exchange between ponded water and soil, revised surface energy fluxes, and topography-based lateral overflow. Initial applications over the Everglades, evaluated against the Everglades Depth Estimation Network (EDEN), demonstrate that the framework can generate realistic seasonal inundation and associated shifts in latent and sensible heat fluxes. These experiments provide a proof-of-concept that surface ponding can be represented dynamically inside an ESM.

The next phase of this work will focus on refining, generalizing, and testing this new wetland hydrology framework across broader wetlandscapes. We will conduct a multi-site evaluation across the EDEN network to constrain key SEEP parameters controlling infiltration, overflow, and clogging-layer resistance, to improve peak water depths, short-term variability, and timing. In parallel, we will extend the surface-water column to allow for dynamically deeper surface-water formations and improve the representation of bathymetry to enhance topographic realism further.

These developments will be integrated into the full LM4.1–ESM4.1 modeling system to assess how improved ponding physics alters land–atmosphere coupling. Finally, the refined hydrologic framework will be coupled to the existing Global Integrated Microbial Interactions with Carbon in Soil (GIMICS) in LM4.1, enabling evaluation of how surface inundation and water-table dynamics regulate CO₂ and CH₄ fluxes across wetlandscapes.

By advancing the physical representation of surface water in ESMs and grounding it in field observations, this work provides a pathway to connect site-scale wetland processes with watershed-scale climate and carbon feedbacks, supporting more realistic assessments of wetland resilience and nature-based climate solutions.