Abstract:
Peatlands are characterized by high soil moisture contents and hydrological dynamics that differ greatly from those in biomes on mineral soils. In combination with peatland-specific vegetation characteristics, this leads to distinct energy and water fluxes across the soilvegetation-atmosphere interface over these environments. Covering 3% of the global land surface, peatlands can be a regionally dominant biome, and thus importantly influence the land surface boundary conditions for weather and climate simulations. However, modeling of peatland hydrology is a challenging task.

In these shallow-groundwater systems, soil moisture of the unsaturated zone, and consequently the energy and water exchange with the atmosphere, is closely coupled to water table depth, which is thus a key variable that must be adequately modeled. We discuss the capability of an operational global land surface model to simulate peatland hydrology. Specifically, we evaluate the Catchment land surface model (CLSM) of the NASA Goddard Earth Observing System version 5 (GEOS-5) modeling and assimilation framework, which is one of the few global land surface models in which water table depth is modeled at all.

A preliminary analysis of groundwater levels from the GEOS-5 Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA-2) and other GEOS-5-based land-only products show very little differences between areas with peatlands and those with dominantly mineral soils. In contrast, observed water table levels show strong differences in temporal statistical moments between peatlands and areas with mineral soils. Therefore, we present an initial attempt to improve the GEOS-5 CLSM performance over peatlands by updating select parameters based on improved ancillary data and parameter optimization, while keeping the current GEOS-5 CLSM structure as used in MERRA-2.