Spatial scale-dependent land–atmospheric methane exchanges in the northern high latitudes from 1993 to 2004

Abstract

Effects of various spatial scales of water table dynamics on land–atmospheric methane (CH₄) exchanges have not yet been assessed for large regions. Here we used a coupled hydrology–biogeochemistry model to quantify daily CH₄ exchanges over the pan-Arctic from 1993 to 2004 at two spatial scales of 100 km and 5 km. The effects of sub-grid spatial variability of the water table depth (WTD) on CH₄ emissions were examined with a TOPMODEL-based parameterization scheme for the northern high latitudes. We found that both WTD and CH₄ emissions are better simulated at a 5 km spatial resolution. By considering the spatial heterogeneity of WTD, net regional CH₄ emissions at a 5 km resolution are 38.1–55.4 Tg CH₄ yr⁻¹ from 1993 to 2004, which are on average 42% larger than those simulated at a 100 km resolution using a grid-cell-mean WTD scheme. The difference in annual CH₄ emissions is attributed to the increased emitting area and enhanced flux density with finer resolution for WTD. Further, the inclusion of sub-grid WTD spatial heterogeneity also influences the inter-annual variability of CH₄ emissions. Soil temperature plays an important role in the 100 km estimates, while the 5 km estimates are mainly influenced by WTD. This study suggests that previous macro-scale biogeochemical models using a grid-cell-mean WTD scheme might have underestimated the regional CH₄ emissions. The spatial scale-dependent effects of WTD should be considered in future quantification of regional CH₄ emissions.