Peatland hydrology in Noah-MP land surface model v5.0: parameterization and evaluation over the Congo peatlands

Abstract. Tropical peatlands are carbon-rich ecosystems primarily governed by water level dynamics, yet they remain inadequately represented in many land surface models (LSMs). The widely used Noah-Multiparameterization (Noah-MP) LSM lacks peatland-specific parameterizations. This study presents enhanced capabilities of Noah-MP LSM v5.0 by implementing peatland-specific modules for microtopography-based subgrid inundation, a water-level-dependent runoff formulation, and evapotranspiration stress functions governed by water-level dynamics, along with the peat soil properties, in a similar way as earlier implemented in the NASA Catchment LSM with peatland-specific modules (PEATCLSM). These options are applied selectively to peat grid cells within the NASA Land Information System (LIS) framework, retaining default model physics elsewhere. We evaluate the scheme over the Cuvette Centrale, the world's largest tropical peatland complex in the central Congo Basin, using in-situ water levels from 20 monitoring wells and terrestrial water storage anomalies (TWSA) from the Gravity Recovery And Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) satellite missions. Four experiments with two different input precipitation sources (MERRA-2 and CHIRPS) are conducted to differentiate the impacts of the peatland module from the default model, using the earlier developed PEATCLSM forced by MERRA-2 as a benchmark. The peat module substantially improves water level estimates, with CHIRPS-forced simulations achieving the highest performance (max correlations up to R~0.92 - 0.95 at Mai-Ndombe with recent water level records) and reduced RMSE and bias relative to both the default Noah-MP and PEATCLSM when evaluated with in-situ data. The new peatland parameterization shifts simulated water levels from unrealistically dry conditions (median = -1.75 to -1.41 m) to wetland dynamics (median = -0.12 to -0.01 m), replacing Hortonian runoff with saturation-controlled subsurface flow (median = 1.78 to 1.87 mm day-1) and reducing evapotranspiration (for CHIRPS reduced from about 3.2 to 2.86 mm day-1), mainly due to waterlogging stress. At the basin scale, agreement with satellite-based TWSA is improved with the inclusion of a proxy river storage component, increasing correlations (R) by up to 11.7% and reducing RMSE by 6.4%. These results underscore the value of explicit representations of peatland hydrology in the Noah-MP LSM and provide a modular basis for future model coupling and data assimilation.