Interannual Covariability Found in Evapotranspiration and Satellite-derived Vegetation Indices over Northern Asia

Abstract

Temporal variation in vegetation over a large area induces temporal variation in the landatmosphere water budget through evapotranspiration activity. To examine this relationship interannually, normalized difference vegetation index (NDVI) and evapotranspiration (ET) values collected from 1982 to 2000 over northern Asia were investigated. Monthly global NDVI values were acquired from Pathfinder AVHRR land data. Monthly ET was estimated from NCEP/NCAR assimilated atmospheric data and CMAP global precipitation data. All calculations were made for 2:5 × 2:5-degree grid boxes in the study region on a monthly basis. The correlation coefficient of the 19-year time series of ET and NDVI anomalies showed the annual maximum correlation in June, and high correlation generally distributed over the region except for southern arid areas and the most northern areas. Although interannual variations in temperature and precipitation anomalies also showed some relation to ET in the warm season, they did not exhibit high correlation in a specific month. Since the vegetation is probably most active in June, it is considered that vegetation variability contributed significantly to ET through its transpiration activity.