Four Decades of Trends in Snowmelt and Greenup over High-latitude Terrestrial Ecosystems

The ongoing climate change has primarily affected snowmelt and greenup timings, which are the two crucial regulators for every component of biogeochemical cycles of the terrestrial ecosystems in high-latitude regions. Previous studies, using various datasets at different regional scales, have focused on either trend, therefore not thoroughly analyzing relative long-term changes in both timings over the entire high-latitudes. In this study, we assessed the four decades (1982-2021) of trends in those two timings for the regions (latitude > 45°N). First, we used Google Earth Engine to derive snowmelt and greenup timings based on normalized indices (i.e., normalized difference snow index and normalized difference vegetation index) that were retrieved from the surface reflectance of Advanced Very High Resolution Radiometer (AVHRR, daily at 0.05°) from National Oceanic and Atmospheric Administration (NOAA) Climate Data Record (CDR). Then, we evaluated those timings against various ground datasets and remote sensing-based estimates, such as PhenoCam, PEP725, SNOTEL, and MODIS. Finally, we investigated the meteorological and geographical effects on the long-term trends of the two timings across the high-latitude regions. Our results imply that the increases in the spatial heterogeneity on snow-free days may considerably alter the spatiotemporal pattern of the vegetation growth and, therefore, the relevant carbon cycle across the high-latitudes.

This study is supported by the National Research Foundation of Korea (NRF) grants funded by the Korea government (MSIT) (2020R1A2C2007670, 2020R1C1C1014886 and 2022R1C1C2009543).