Role of Snow on the Spring Leaf Onset in the Tundra Ecosystems with NCAR CLM5

Snow melting is a significant factor in the growth of grasses in tundra ecosystems. Snow melting leads the cooling effects: snow depth decreases between the first day of the year at which air temperature goes above 0 ℃ (TOA) and which soil temperature goes above 0℃ (TOS). This is important for the start of vegetation growing season (SOS) because the grass can start to grow after the TOS. Most of the TOS trend is affected by air temperature, but not always. Despite an accelerated TOA trend, the TOS trend can be delayed in the regions where the snow depth at the point at which snow begins to melt shows an increasing trend. And thus, the SOS does not correspond with temperature anomalies but is affected by the impact of interaction between temperature and amount of accumulated snow. In order to identify the impact of snow pattern on SOS, we designed two numerical experiments with NCAR Community Land Model (CLM) ver. 5 for the arctic regions above 50 degrees north from 1971 to 2010: one control simulation and the other experimental simulation with removing the snow trend, which is increased in the observation. In the experimental simulation, constant snow patterns result in similar TOS and TOA trends, while TOS trend is delayed in comparison to the accelerated TOA trend in the northern Europe and Nunavut of northern Canada in the control simulation. As such, an upward tendency of total snow could explain the delays in TOS and SOS trends observed in northern Europe and Nunavut. Although global warming is expected to accelerate SOS and TOS trends by increasing air temperature, upward total snow trends can result in the opposite effect. With these results, we propose the possibility that vegetation germination could be delayed even during a warmer climate in blooming season due to increase in total snow.

AcknowledgementsThis research was supported by a National Research Foundation of Korea Grant from the Korean Government (NRF-2016M1A5A1901769/KOPRI-PN19081 and NRF-2018R1A1A3A04079419).