Climate drivers of Arctic tundra variability and change using an indicators framework

Abstract

This study applies an indicators framework to investigate climate drivers of tundra vegetation trends and variability over the 1982–2019 period. Previously known indicators relevant for tundra productivity (summer warmth index, coastal spring sea-ice area, coastal summer open-water) and three additional indicators (continentality, summer precipitation, and the Arctic Dipole: second mode of sea level pressure variability) are analyzed with maximum annual Normalized Difference Vegetation Index (MaxNDVI) and the sum of summer bi-weekly (time-integrated) NDVI (TI-NDVI) from the Advanced Very High Resolution Radiometer (AVHRR) time-series. Climatological mean, trends, and correlations between variables are presented. Changes in sea ice continue to drive variations in the other indicators. As spring sea ice has decreased, summer open water, summer warmth, MaxNDVI, and TI-NDVI have increased. However, the initial very strong upward trends in previous studies for MaxNDVI and TI-NDVI are weakening and becoming spatially and temporally more variable as the ice retreats from the coastal areas. TI-NDVI has declined over the last decade particularly over High Arctic regions and southwest Alaska. The Continentality Index (maximum minus minimum monthly temperatures) is decreasing across the tundra, more so over North America than Eurasia. The relationship has weakened between sea-ice and summer warmth index and TI-NDVI, as the maritime influence of open water has increased along with total precipitation. The winter Arctic Dipole is correlated in Eurasia with spring sea ice, summer open water, MaxNDVI, TI-NDVI, the continentality index and total summer precipitation. This winter connection to tundra emphasizes the role of sea ice in driving the summer indicators. The winter (DJF) Arctic Dipole drives sea ice variations which in turn shape summer open water, the atmospheric summer warmth index and NDVI anomalies. The winter and spring indicators represent potential predictors of tundra vegetation productivity a season or two in advance of the growing season.