DEGCR + AGCR unit/IASC all meeting

"Phenology" is a term to characterize the recursive events occurred in vegetation communities, such as leaf-fush, flowering, leaf-fall. In this study, I focus on the periodic timings of plant leaves: leaf-flush, and leaf-fall.

Latitudinal gradient of start of the growing season (SOS, related leaf-flush) and end of the growing season (EOS, related leaf-fall) events were quantified in Alaska (61 °N to 71 °N) using satellite- and ground-based data sets. The Alaskan evergreen needleleaf forests are sparse and the understory vegetation has a substantial impact on the satellite signal. We evaluated the SOS and EOS of understory and tundra vegetation using the time-lapse camera images. From the comparison of three different SOS methods from two satellite data sets (SPOT-VEGETATION and Terra-MODIS), we found that the satellite-based SOS timing was slightly earlier than the ground-based SOS but consistent with the leaf appearance of the forest understory and tundra vegetation. The averaged SOS over multiple methods can be a measure of spring leaf appearance for understory and tundra vegetation. On contrary, the relationship between the ground- and satellite-based EOSs was not as strong as that of SOS both for boreal forest and tundra sites because of the large biases between those two EOSs (19 to 26 days). The satellite-based EOS was more relevant to the snow-fall events than the senescence of understory or tundra. Plant canopy radiative transfer simulation suggested that a 84-86% of the NDVI seasonal amplitude can reasonably be a threshold for EOS determination. The latitudinal gradients of SOS and EOS evaluated by the satellite and ground data were consistent and the satellite-based SOS and EOS were 3.5 to 5.7 day/degree and -2.3 to -2.7 day/degree, which corresponded to the spring (May) temperature sensitivity of -2.5 to -3.9 day/°C in SOS and autumn (August and September) temperature sensitivity of 3.0 to 4.6 day/°C in EOS. As the average air temperature in Arctic region rose up to 1.36 °C in the first decade of the 21th century (Bekryaev et al., 2010; Hinzman et al., 2013), such increase in the air temperature could have affected the SOS and EOS timings if the phenology timings are primarily regulated by the temperature. Assuming temperature gradients of SOS and EOS can be evaluated from the latitudinal gradient of phenology and temperature, average phenology timings in the first decade of 21st century may have been advanced by 4.4 days (SOS) and delayed by 5.2 days (EOS) across the state of Alaska. These estimates should be validated through a detail and long-term data analysis in the future.

IACE, which is a research center for the Arctic region of JAMSTEC, has been settled in this April. It is expected to contribute to the Arctic Council and Japanese government via providing them the scientific basis for decision-making under the ArCS project supported by the MEXT.
A tentative activity plan of our research relating with the SLCFs (short-lived climate forcers) including black carbon aerosols and methane will be shown in this presentation. Any suggestions, comments, and possible collaborations are appreciated.