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[1] Ecosystems along the 0°C mean annual isotherm are arguably among the most sensitive to changing climate and mires in these regions emit significant amounts of the important greenhouse gas methane (CH 4 ) to the atmosphere. These CH 4 emissions are intimately related to temperature and hydrology, and alterations in permafrost coverage, which affect both of those, could have dramatic impacts on the emissions. Using a variety of data and information sources from the same region in subarctic Sweden we show that mire ecosystems are subject to dramatic recent changes in the distribution of permafrost and vegetation. These changes are most likely caused by a warming, which has been observed during recent decades. A detailed study of one mire show that the permafrost and vegetation changes have been associated with increases in landscape scale CH 4 emissions in the range of 22-66% over the period 1970 to 2000.

Thawing permafrost in the sub-Arctic has implications for the physical stability and biological dynamics of peatland ecosystems. This study provides an analysis of how permafrost thawing and subsequent vegetation changes in a sub-Arctic Swedish mire have changed the net exchange of greenhouse gases, carbon dioxide (CO 2 ) and CH 4 over the past three decades. Images of the mire (ca. 17 ha) and surroundings taken with film sensitive in the visible and the near infrared portion of the spectrum, [i.e. colour infrared (CIR) aerial photographs from 1970 and 2000] were used. The results show that during this period the area covered by hummock vegetation decreased by more than 11% and became replaced by wet-growing plant communities. The overall net uptake of C in the vegetation and the release of C by heterotrophic respiration might have increased resulting in increases in both the growing season atmospheric CO 2 sink function with about 16% and the CH 4 emissions with 22%. Calculating the flux as CO 2 equivalents show that the mire in 2000 has a 47% greater radiative forcing on the atmosphere using a 100-year time horizon. Northern peatlands in areas with thawing sporadic or discontinuous permafrost are likely to act as larger greenhouse gas sources over the growing season today than a few decades ago because of increased CH 4 emissions. Correspondence: Torbjö rn Johansson, tel. 1 46 0 46 222 39 74, fax 1 46 0 46 222 40 11, *The water fluxes of CO 2 -C and CH 4 -C used for scaling are not measured at the Stordalen mire. w The whole mire values are area-weighted averages except for the total carbon accumulated. zThe CH 4 -C value used is a median value. gs, growing season 5 153 days.

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[1] Although much attention in recent years has been devoted to methane (CH 4 ) emissions from northern wetlands, measurement based data sets providing full annual budgets are still limited in number. This study was designed to help fill the gap of year-round measurements of CH 4 emissions from subarctic mires. We report continuous eddy correlation CH 4 flux measurements made during 2006 and 2007 over the Stordalen mire in subarctic Sweden (68°20′N, 19°03′E, altitude 351 m) using a cryocooled tunable diode laser. The landscape-scale CH 4 fluxes originated mainly from the permafrost free wet parts of the mire dominated by tall graminoid vegetation. The midseason average CH 4 emission mean was 6.2 ± 2.6 mg m −2 h −1 . A detailed footprint analysis indicates an additional strong influence on the flux by the nearby shallow Lake Villasjön (0.17 km 2 , maximum depth 1.3 m). A stable bimodal distribution of wind flow from either the east or the west allowed separating the lake and mire vegetation signals. The midseason lake emission rates were as high as 12.3 ± 3.3 mg m −2 h −1 . Documented CH 4 fluxes are similar to results obtained by automatic chamber technique and higher than manual chamber measurements made in the wet minerotrophic section dominated by Eriophorum angustifolium. The high fluxes observed from this vegetation type are significant because the areal distribution of this source in the mire is expanding due to ongoing thawing of the permafrost. A simple peat temperature relationship with CH 4 emissions was used to fill data gaps to construct a complete annual budget of CH 4 fluxes over the studied area. The calculated annual CH 4 emissions in 2006 and 2007 equaled 24.5 and 29.5 g CH 4 m −2 yr −1 , respectively. The summer season CH 4 emissions dominated (65%) the annual flux, with the shoulder seasons of spring and autumn significant (25%) and a minor flux from the winter (10%).

[1] A greenhouse gas inventory can for some ecosystems be based solely on the net CO 2 exchange with the atmosphere and the export of dissolved organic carbon. In contrast, the global warming effect may be more complex in ecosystems where other greenhouse gases such as CH 4 or N 2 O have significant exchanges with the atmosphere. Through micrometeorological landscape-scale measurements from the largest wetlands on Earth in West Siberia we show that CH 4 has a stronger effect than CO 2 on the greenhouse gas budget in terms of radiative forcing on the atmosphere. Direct measurements of the CO 2 and CH 4 exchange during the summer of 1999 show that these wetland ecosystems, on average, acted as net sinks of carbon of 0.5 g C m À2 day À1but large net sources of CH 4 . Given the high Global Warming Potential of CH 4 , the Siberian wetlands are an important source of radiative forcing, even in comparison to anthropogenic emissions.

Abstract. Estimating evaporation is important when managing water resources and cultivating crops. Evaporation can be estimated using land surface heat flux models and remotely sensed land surface temperatures (LST), which have recently become obtainable in very high resolution using lightweight thermal cameras and Unmanned Aerial Vehicles (UAVs). In this study a thermal camera was mounted on a UAV and applied into the field of heat fluxes and hydrology by concatenating thermal images into mosaics of LST and using these as input for the two-source energy balance (TSEB) modelling scheme. Thermal images are obtained with a fixed-wing UAV overflying a barley field in western Denmark during the growing season of 2014 and a spatial resolution of 0.20 m is obtained in final LST mosaics. Two models are used: the original TSEB model (TSEB-PT) and a dual-temperaturedifference (DTD) model. In contrast to the TSEB-PT model, the DTD model accounts for the bias that is likely present in remotely sensed LST. TSEB-PT and DTD have already been well tested, however only during sunny weather conditions and with satellite images serving as thermal input. The aim of this study is to assess whether a lightweight thermal camera mounted on a UAV is able to provide data of sufficient quality to constitute as model input and thus attain accurate and high spatial and temporal resolution surface energy heat fluxes, with special focus on latent heat flux (evaporation). Furthermore, this study evaluates the performance of the TSEB scheme during cloudy and overcast weather conditions, which is feasible due to the low data retrieval altitude (due to low UAV flying altitude) compared to satellite thermal data that are only available during clear-sky conditions. TSEB-PT and DTD fluxes are compared and validated against eddy covariance measurements and the comparison shows that both TSEB-PT and DTD simulations are in good agreement with eddy covariance measurements, with DTD obtaining the best results. The DTD model provides results comparable to studies estimating evaporation with similar experimental setups, but with LST retrieved from satellites instead of a UAV. Further, systematic irrigation patterns on the barley field provide confidence in the veracity of the spatially distributed evaporation revealed by model output maps. Lastly, this study outlines and discusses the thermal UAV image processing that results in mosaics suited for model input. This study shows that the UAV platform and the lightweight thermal camera provide high spatial and temporal resolution data valid for model input and for other potential applications requiring high-resolution and consistent LST.