Pan-Arctic trends (1982-2006) in temperature and bioclimatological indicators

Warming induced changes in Arctic vegetation have to date been studied mostly through field studies, or through the examination of trends in a single bioclimatological indicator over time. The central objective of this study was to analyze pan-Arctic trends in temperature in relation to four established bioclimatological indicators: spring onset, autumn onset, maximum annual Normalized Difference Vegetation Index (NDVI) and total annual Net Primary Productivity (NPP). A secondary objective was to assess agreement in short-term trends between model and field measured NPP. The following data sources were used: Advanced Very High Resolution Radiometer Polar Pathfinder Extended for temperature; 2) Global Inventory Modeling and Mapping Studies for NDVI; and 3) Global Productivity Efficiency Model for NPP. Data sets were processed in Matlab, and regional scale trends were analyzed statistically using Mann-Kendall's test and Sen's slope. Increases in temperature, total annual NPP and maximum annual NDVI were observed. Many of the observed rises are located in regions of Alaska that have been the focus of numerous field studies. Increases in NDVI and NPP were found to be closely associated with increases in temperature, which indicates warming induced changes in Arctic carbon cycling and biomass. Variations in spring and autumn onset dates were largely non-significant although field studies have found significant shifts to earlier spring onset. Comparisons of the model NPP trend to a time series of field NPP estimates indicated low agreement, indicating a need for better calibration of Arctic NPP estimates. Conclusions focus on implications of these findings for future work.