The influence of soil moisture and evapotranspiration (ET) on ecosystem dynamics has been studied only in a limited way owing to a lack of large-scale measurements. In this study, the Normalized Difference Vegetation Index (NDVI) data retrieved by using the Moderate Resolution Imaging Spectroradiometer (MODIS) was successfully used to identify ecological relationships that involve soil moisture and ET at 132 sites located in different continents of the world. Optimal relationships exist between NDVI and soil moisture within time lags of 10 days at forest and grassland sites, and of 25 days at cropland and shrubland sites. The ecological correlations between NDVI and the hydrologic variables are affected mainly by the land-cover type. The densely vegetated areas show shorter time lags for NDVI to ET owing to canopy evaporation and plant transpiration which are almost simultaneous with NDVI.