Abstract
Abstract. In this study we present the development of the dynamical wetland extent scheme (DWES) and evaluate its skill to represent the global wetland distribution. The DWES is a simple, global scale hydrological scheme that solves the water balance of wetlands and estimates their extent dynamically. The extent depends on the balance of water flows in the wetlands and the slope distribution within the grid cells. In contrast to most models, the DWES is not directly calibrated against wetland extent observations. Instead, wetland affected river discharge data are used to optimise global parameters of the model. The DWES is not a complete hydrological model by itself but implemented into the Max Planck Institute – Hydrology Model (MPI-HM). However, it can be transferred into other models as well. For present climate, the model evaluation reveals a good agreement for the spatial distribution of simulated wetlands compared to different observations on the global scale. The best results are achieved for the Northern Hemisphere where not only the wetland distribution pattern but also their extent is simulated reasonably well by the DWES. However, the wetland fraction in the tropical parts of South America and Central Africa is strongly overestimated. The simulated extent dynamics correlate well with monthly inundation variations obtained from satellites for most locations. Also, the simulated river discharge is affected by wetlands resulting in a delay and mitigation of peak flows. Compared to simulations without wetlands, we find locally increased evaporation and decreased river flow into the oceans due to the implemented wetland processes. In summary, the evaluation demonstrates the DWES' ability to simulate the distribution of wetlands and their seasonal variations for most regions. Thus, the DWES can provide hydrological boundary conditions for wetland related studies. In future applications, the DWES may be implemented into an Earth system model to study feedbacks between wetlands and climate.
Highlights
In recent studies wetlands are suspected to play an important role during periods of climate change (e.g. Ringeval et al, 2011; Gedney et al, 2004; Levin et al, 2000)
In this study we present the development of the dynamical wetland extent scheme (DWES) and evaluate its skill to represent the global wetland distribution
It ranges from −1 for observed wetlands that are not simulated by the Max Planck Institute – Hydrology Model (MPI-HM) to 1 for simulated wetlands that are not seen in the observations
Summary
In recent studies wetlands are suspected to play an important role during periods of climate change (e.g. Ringeval et al, 2011; Gedney et al, 2004; Levin et al, 2000). The representation of the wetland’s spatial extent and its temporal variations is still a weak point in today’s Earth System Models (ESMs) and needs to be improved by a better simulation of their hydrological cycle (O’Connor et al, 2010; Ringeval et al, 2010). The water level is an important factor for the wetland’s biogeochemistry which results in carbon sequestration or decomposition (e.g. O’Connor et al, 2010, and references therein). In the saturated soil zone, below the water table, anoxic conditions prevail which are favourable for methane producing microbes. It can be oxidised to CO2 within the unsaturated oxic soil zone above the water table. The water table determines the separation of soil into a methane producing and a methane oxidising zone. While most studies identify wetlands as net carbon sinks for today’s climate conditions (Bohn et al, 2007; Gorham, 1991; Friborg et al, 2003), a number of studies concluded that some wetlands might turn into carbon sources in a warmer climate (St-Hilaire et al, 2010; Gorham, 1991) due to higher productivity of methane releasing microbes
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