How well can we model wetlands in tropical and boreal regions?

Dadson, Simon; Gedney, Nicola; Hayman, Garry; Clark, Douglas; Blyth, Eleanor; Taylor, Christopher; Prigent, Catherine. 2011 How well can we model wetlands in tropical and boreal regions? [Lecture] In: 3rd iLEAPS Science Conference, Garmisch-Partenkirchen, Germany, 18-23 September 2011.

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The role of wetlands in the global methane cycle is the subject of much current interest. Wetlands are generally accepted as being the largest, but least well quantified, single source of methane (CH4), with recent emission estimates ranging from 105-278 Tg yr-1. The majority of naturally-produced CH4 comes from bacteria in wetlands when organic material decomposes under water-logged anaerobic conditions. Their productivity is a function of (i) soil temperature (which governs microbial process rates); (ii) water table depth (which sets the depth of the CH4-generating region); and (iii) the carbon content of the decomposable substrate (which is modulated by factors such as precipitation, permafrost dynamics, vegetation cover, and topography). Tropical wetlands contribute ~75% of global wetland CH4 emissions. The largest fluxes are over South America, equatorial Africa and south-east Asia. These regions also have the highest uncertainties in CH4 emission. In the tropics, inundation by surface water is a particularly important mechanism for wetland formation, mainly because natural and human-induced variations in wetland extent lead to variability in water, heat, and CH4 fluxes. Here, wetland formation is driven by seasonal hydrological variability and a key control on the CH4 emissions is the water table level. Quantifying natural variability in wetland CH4 emissions is therefore vital not only if we want to understand the hydrological drivers of natural CH4 emissions, but also to avoid having natural variability mask anthropogenic emissions. Although the emissions of methane from the wetlands and lakes of the boreal region are smaller than those from tropical wetlands, the size and remoteness of the boreal region pose a significant challenge to the quantification of both terrestrial ecosystem processes and their feedbacks to regional and global climate. In recent years, Earth Observation (EO) data have demonstrated the potential to become a major tool for characterizing the main processes and estimating key variables governing the land-atmosphere interface. In this paper, we present a summary of recent work on modelling hydrological and biogeochemical aspects of wetland formation and the associated methane cycle in African and boreal environments: • African wetlands: We have developed an inundation model of the evaporative losses that occur over the Niger inland delta by adding an overbank flow parameterization to the Joint UK Land‐Environment Simulator (JULES, land surface model. The hydrological component comprises a probability‐distributed model of soil moisture and runoff production coupled with a discrete approximation to the one‐dimensional kinematic wave equation to route river water down slope [8]. Topographic data at subgrid‐resolution was used to derive a two‐parameter frequency distribution of inundated areas for each grid box which was then employed to represent overbank inundation in the model. • Boreal wetlands: We have been investigating new parameterisations of methane generation from wetlands (also applicable to African wetlands). Further, through the ESA ALANIS Methane project, we are exploring the use of new Earth Observation products relevant to boreal wetlands to evaluate the treatment of methane wetlands processes in the JULES UK community land surface model. The JULES model is being used in three configurations of increasing complexity: 1. Site specific: The model is run for a single point and calculates the vertical fluxes of water, carbon, methane and energy at sub-diurnal time-steps given the driving meteorological variables. 2. Offline distributed: The land surface is represented on a grid and the driving data vary at the same spatial resolution. The EO data can be used as a driving dataset or as a constraint. 3. Fully-coupled: JULES is integrated as the land surface component in a fully-coupled and interactive (regional) climate model with atmospheric chemistry. Model configurations 2 and 3 provide a unique evaluation of the CH4 fluxes from runs in spatially-distributed mode across boreal Eurasia, using the EO data to define the wetland extent and to constrain key surface parameters that control the surface temperature and snow cover (snowmelt, freeze-thaw).

Item Type: Publication - Conference Item (Lecture)
Programmes: CEH Topics & Objectives 2009 onwards > Biogeochemistry > BGC Topic 2 - Biogeochemistry and Climate System Processes > BGC - 2.3 - Determine land-climate feedback processes to improve climate model predictions
CEH Sections: Reynard
Additional Information. Not used in RCUK Gateway to Research.: Abstract freely available online - click on Official URL link
NORA Subject Terms: Hydrology
Earth Sciences
Atmospheric Sciences
Related URLs:
Date made live: 04 Apr 2012 10:42

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