Tropical Peatland Hydrology Simulated With a Global Land Surface Model

Abstract

Tropical peatlands are among the most carbon-dense ecosystems on Earth, and their water storage dynamics strongly control these carbon stocks. The hydrological functioning of tropical peatlands differs from that of northern peatlands, which has not yet been accounted for in global land surface models (LSMs). Here, we integrated tropical peat-specific hydrology modules into a global LSM for the first time, by utilizing the peatland-specific model structure adaptation (PEATCLSM) of the NASA Catchment Land Surface Model (CLSM). We developed literature-based parameter sets for natural (PEATCLSM Trop,Nat ) and drained (PEATCLSM Trop,Drain ) tropical peatlands. Simulations with PEATCLSM Trop,Nat were compared against those with the default CLSM version and the northern version of PEATCLSM (PEATCLSM North,Nat ) with tropical vegetation input. All simulations were forced with global meteorological reanalysis input data for the major tropical peatland regions in Central and South America, the Congo Basin, and Southeast Asia. The evaluation against a unique and extensive data set of in situ water level and eddy covariance-derived evapotranspiration showed an overall improvement in bias and correlation compared to the default CLSM version. Over Southeast Asia, an additional simulation with PEATCLSM Trop,Drain was run to address the large fraction of drained tropical peatlands in this region. PEATCLSM Trop,Drain outperformed CLSM, PEATCLSM North,Nat , and PEATCLSM Trop,Nat over drained sites. Despite the overall improvements of PEATCLSM Trop,Nat over CLSM, there are strong differences in performance between the three study regions. We attribute these performance differences to regional differences in accuracy of meteorological forcing data, and differences in peatland hydrologic response that are not yet captured by our model. Plain Language SummaryTropical peatlands are wetlands in which plant material accumulates under waterlogged conditions and develops into a dense organic soil layer. Disturbance of their selfregulating hydrology by external factors such as artificial drainage, land use change, and climate change can quickly convert these immense carbon stocks into strong sources of greenhouse gases. Including the hydrology of tropical peatlands into global Earth system models allows us to understand the impact of such external disturbances. We developed the first hydrology modules for natural and drained tropical peatlands to plug into the NASA Goddard Earth Observing System modeling framework. Our results display strong regional differences, and indicate that the accuracy of our model is limited by rainfall data quality and by our understanding of how peatland hydrology differs across the three regions that contain the major tropical peatland areas (Central and South America, the Congo Basin, and Southeast Asia). Nonetheless, simulations

KAPAS II: simulation of peatland wildfires with daily variations of peat moisture content

“…The peat MC data were obtained from simulations conducted with the peat-specific land surface model in Apers et al (2022), using the tropical version of the peat-specific land surface model developed by Bechtold et al (2019). The model in Apers et al (2022) was specifically developed and extensively evaluated for tropical peatland conditions and was shown to perform best over southeast Asian peatlands.…”

“…The peat MC data were obtained from simulations conducted with the peat-specific land surface model in Apers et al (2022), using the tropical version of the peat-specific land surface model developed by Bechtold et al (2019). The model in Apers et al (2022) was specifically developed and extensively evaluated for tropical peatland conditions and was shown to perform best over southeast Asian peatlands. This model was based on the Catchment Land Surface Model (CLSM) of the NASA GEOS (Goddard Earth Observing System) Earth System Modelling framework and has two modules, one for drained tropical peatlands (PEATC-LSM Trop,Drain ) and one for natural tropical peatlands (PEAT-CLSM Trop,Nat ); these different peatland types have distinct hydrological conditions and thus have different peat MC characteristics (Apers et al 2022).…”

“…The model in Apers et al (2022) was specifically developed and extensively evaluated for tropical peatland conditions and was shown to perform best over southeast Asian peatlands. This model was based on the Catchment Land Surface Model (CLSM) of the NASA GEOS (Goddard Earth Observing System) Earth System Modelling framework and has two modules, one for drained tropical peatlands (PEATC-LSM Trop,Drain ) and one for natural tropical peatlands (PEAT-CLSM Trop,Nat ); these different peatland types have distinct hydrological conditions and thus have different peat MC characteristics (Apers et al 2022). Canal construction had been under way in central Kalimantan since the 1990s (Ritzema et al 2014), and we found a number of canals inside our study area based on the canal map produced by Dadap (2020); therefore, we assumed that the peatland under the study area was drained.…”

“…Canal construction had been under way in central Kalimantan since the 1990s (Ritzema et al 2014), and we found a number of canals inside our study area based on the canal map produced by Dadap (2020); therefore, we assumed that the peatland under the study area was drained. From this assumption, the PEATCLSM Trop,Drain model in Apers et al (2022) was used to obtain the peat MC data for KAPAS II. We used the soil surface MC (0-5 cm depth) instead of a deeper MC, because the ignition of smouldering wildfires most of the time occurs at the surface.…”

“…The MC information obtained from the model in Apers et al (2022) was volumetric (volume-based), whereas that used in KAPAS II is gravimetric (mass-based). Thus, to obtain gravimetric MC data, we divided the volumetric MC by the peat bulk density (in g/cm 3 ).…”