18 January 2018

Observed and CMIP5-Simulated Sensitivities of Spring Greenup to Preseason Climate

Temperature Changes are the Dominant Control on Observed Mid- to High-Latitude Spring Greenup Advances Since 1982

Science

We found that satellite observations indicate an advancement of mid- to high-latitude spring greenup (SG) by about 1 day per decade, with significant spatial heterogeneity. The SG sensitivity to preseason temperature dominates over precipitation, but biomes that are more sensitive to temperature are also more sensitive to precipitation. Large biases in individual CMIP5 earth system models (ESMs) imply needed model improvements to climate prediction and phenological process parameterizations.

Impact

High-latitude carbon cycle responses to CO2 and climate are critical for global predictions of the terrestrial C cycle. We show here that most current ESMs fail to accurately represent early growing season dynamics in high-latitude systems, implying uncertainty in feedbacks with the atmosphere. Further, these types of observationally-inferred benchmarks can be used to test and improve large-scale land models.

Summary

Vegetation phenology plays an important role in regulating land-atmosphere energy, water, and trace-gas exchanges. We used satellite-derived vegetation indices generated SG and climate reanalysis data to investigate the SG responses to preseason climate change in high-latitude regions. We compared these observed responses to simulated SG responses to preseason climate inferred from CMIP5 ESMs. The observationally-inferred SG suggests that there has been an advance of about 1 day per decade in the northern mid to high latitudes, with significant spatial heterogeneity. The spatial heterogeneity of the SG advance results from heterogeneity in the change of preseason climate and vegetation responses. The SG to preseason temperature sensitivity is highest in forests other than deciduous needleleaf forests. Although the extent of regions where the SG is sensitive to preseason precipitation is smaller, biomes that are more sensitive to temperature are also more sensitive to precipitation, suggesting interactive controls. In the mean, the CMIP5 ESMs reproduced the dominant latitudinal preseason climate trends and SG advances. However, large biases in individual ESMs for preseason climate and SG sensitivity imply needed model improvements to climate prediction and phenological process parameterizations.

Contact
William J. Riley
Lawrence Berkeley National Laboratory
Publications
Jia, G. "Observed and Simulated Sensitivities of Spring Greenup to Preseason Climate in Northern Temperate and Boreal Regions." Journal of Geophysical Research: Biogeosciences (2018). [10.1002/2017jg004117].