Satellite-derived vegetation index and evapotranspiration estimated by using assimilated atmospheric data over Asia

The monthly evapotranspiration (ET), which was estimated from assimilated atmospheric data from European Centre from Medium-Range Weather Forecasts (ECMWF) and gridded global precipitation data introduced by Xie and Arkin, was examined in relation to the vegetation activity for 1987 and 1988 over Asia. The vegetation activity was represented by the Normalized Difference Vegetation Index (NDVI) that was calculated from satellite observation. Over Siberia, the annual marches of the ET and the NDVI were quite similar. Furthermore, bimodal annual variations of the NDVI and ET were observed in Punjab (around Pakistan and northern India) where bi-seasonal cultivation is seen. The ET-NDVI relationships were analyzed for seven vegetational cover types and revealed that slopes of ET-NDVI regression lines are distinguished depending on the vegetation types. The results presented in this paper demonstrate the possibility of investigating the continental-scale vegetation activity and the ET, which is derived from assimilated gridded global data.