Using data from the now redundant Advanced Microwave Scanning Radiometer Earth Observing System (AMSR-E), the group looked at changes in surface water inundation in the boreal Arctic and how this impacts regional methane emissions.

“Most models treat surface water inundation as a static value,” said Jennifer Watts from the University of Montana, US. “We know that surface water in the boreal Arctic changes over time, with some areas turning to wetlands while others dry out. If water inundation is seen as a static value and drier periods are not accounted for, there is a risk that methane emissions from this region may be overestimated. We wanted to investigate whether this is the case.”

Watts and her colleagues conducted a series of carbon and climate sensitivity simulations using the Joint UK Land Environment Simulator (JULES) methane emissions model, with AMSR-E data, which has a resolution of 25 km. They looked at the proportional surface water cover within an AMSER-E grid cell at 15-day, monthly and annual intervals, including inundated soils, open water and landscapes with emergent vegetation.

“Previous studies have largely been constrained to small regions,” Watts told environmentalresearchweb. “We wanted to get a better picture of what is happening over the whole region. We found that while there is widespread wetting across the Arctic continuous permafrost zone, at the same time this is contrasted by surface drying in boreal Canada, Alaska and western Eurasia.”

Using this information to calculate methane emissions, the group found that Arctic wetting and summer warming increased wetland emissions by 0.56 Tg of methane per year compared with the 2003–2011 mean. But this was mainly offset by decreasing emissions (–0.38 Tg CH4 per year) in sub-Arctic areas experiencing surface drying or cooling.

The researchers also found that using monthly or annual inputs resulted in an overestimation of the amount of methane emitted. “Inundation increased by 6–15% when using monthly inputs instead of the 15-day interval data and by 13–31% when using annual inputs,” said Watts. “This highlights that we need to think carefully about how we account for surface inundation in models. It clearly is a dynamic process and treating it as a static process can lead to inaccurate conclusions.”

Watts and her colleagues hope to use the recently-launched AMSR2 instrument onboard the GCOM-W satellite and NASA’s Soil Moisture Active Passive (SMAP) mission to continue their work in this area. The AMSR2 sensor can measure surface water temperature to within 0.5°C while the SMAP sensors can measure surface soil moisture at 1–2 day intervals and at a resolution of less than 10 km.

“We are excited about the prospect of using these new instruments,” said Watts. “More than 50% of the global soil organic carbon pool is stored in the boreal Arctic region. Moist soils are particularly vulnerable to carbon loss as methane, and as surface temperatures continue to rise, it is important we get an accurate estimate of the amount of methane emitted from this region. These new instruments will help us do that.”

The team reported the results in Environmental Research Letters (ERL) as part of the ERL Focus on the Impact of Climate Change on Wetland Ecosystem Carbon Dynamics.

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