A regional phenology model for detecting onset of greenness in temperate mixed forests, Korea: an application of MODIS leaf area index

A regional phenology model for detecting onset of vegetation greenness was developed using year 2001MODIS land products in temperate mixed forests in Korea. The model incorporates a digital elevation model (DEM), moderate resolution imaging spectroradiometer (MODIS) landcover and leaf area index (LAI) products, and climate data from weather-monitoring stations. MODIS-based onset of greenness varied spatially and showed significant correlation with air temperature (r = 0.70, p < 0.001). Our modeling methodology is to relate thermal summation calculated using the MODIS-based timing of onset with 30-year mean air temperature. Onset of greenness is expected to occur at values above the critical thermal summation threshold and is predicted to vary spatially. An algorithm for downscaling 8day composite MODIS LAI product to a daily unit was introduced, and its predictability was validated using ground-measured onset of greenness. Two unknown parameters and the best regression were determined by iterative cross-validation. Minimal cross-validation errors between the predicted and MODIS-based timings of onset were found at a mean absolute error (MAE= 3.0 days) and bias (+ 1.6 days). The predicted onsets show good agreement with ground-measured onset of greenness (MAE= 2.5 days and bias= + 2.5 days). This study demonstrates the utility of MODIS land products as tools for detecting spatial variability in phenology across climate gradients. D 2003 Elsevier Science Inc. All rights reserved.