IFPRI

INTERNATIONAL FOOD POLICY RESEARCH INSTITUTE

Delayed Impact of the North Atlantic Oscillation on Biosphere

Productivity in Asia

Guiling WangLiangzhi You

International Conference on Climate Change and Food Security

Beijing, November 07, 2011

NAOMotivationData and Method

Panel Data of Chinese Crop yields

NDVI

ResultsConclusions

Outline

North Atlantic Oscillation (NAO)

NAO: an oscillation in the gradient of atmospheric pressure between the high pressure center near the Azores and the low pressure center near Iceland on the Atlantic .Through its impact on atmospheric circulation, NAO regulates climate variability in most of the Northern Hemisphere.Positive vs. negative phases of NAO

Motivation

Impact on flora and fauna patterns Although the NAO-related temperature pattern extends far eastward into northern Asia, few documented studies so farBased on the current notion of the NAO phenomenon, a time lag longer than a few months in vegetation response is neither expected nor easily explained

Our Study

We investigate the impact of NAO on the productivity of vegetation in Asia at various time lagsWe found that the vegetation response time in Asia is even longer, at a surprising 18 months

Our Data

Chinese provincial crop yield data from 1979-1997: rice, wheat, maize, sorghum, millet, potato, and soybeanSatellite-derived monthly Normalized Difference Vegetation Index (NDVI)-”Greenness Index”The monthly NDVI data was derived from the Advanced Very High Resolution Radiometer. It spans the period 1982-2000, and covers the globe with a 1-degree spatial resolution

Our Data (Continued)

PC-based NAO index during the extended winter (December through March), provided by NCAR

Our Method - Correlation Analysis

A relationship as being significant only if all of the following four conditions are met:» the correlation based on raw data is significant» the correlation based on detrended data is

significant» detrending the data does not change the sign of

the correlation coefficient» the above three criteria are met in at least one

contingent area that is larger than the size of three medium provinces in China

Correlation coefficients between winter NAO index and crop yields

Correlation between winter NAO index and monthly NDVI in subsequent spring

Correlation between winter NAO index and NDVI in the 2nd growing season

Correlation between the NAO index and NDVI

Three CharacteristicsThe time lag between the NAO index and NDVI is approximately the same as that between the NAO index and crop yieldThe time of significant NAO association identified from the NDVI data (i.e., July-October) covers most of the growing season of the crops for which our crop data establishes a delayed response to NAOThe region of significant NAO-NDVI correlation in Asia covers the northern China where crop yield data suggests a delayed response of vegetation productivity to NAO

Findings

The crop yield data from China and the satellite NDVI data are consistentA significant response of vegetation productivity in Asia to the NAO system with a time delay of one and half years

Discussion

The significant response of vegetation productivity in Asia to NAO with a delay as long as 1.5 years indicates that the lasting memory may reside in some large scale forcing The role of the Arctic Ocean?

Implications

Studies linking carbon dynamics to modes of atmospheric circulation should take into account this delayed response in biosphere carbon assimilationThe timing difference between Europe and Asia in their ecological responses to NAO demands separate treatment of these two continents in many studies NAO index as a weather-related predictor for long-range forecast of several grain crop yields in North Asia

The first paper already published in Geophysical Research Letter

New Research

North Atlantic Oscillation as a long-range forecast of crop yield in North Asia, in particular North KoreaNSF-funded project(2011-2014): A Pilot Project on Interactive Climate and Land Use Predictions

Thank You All!