Study on Influence of Rainfall Distribution on NDVI Anomaly over the Arid Regions in Mongolia Using an Operational Weather Radar

Abstract

The influence of rainfall distribution on NDVI (Normalized Difference Vegetation Index) anomaly was qualitatively investigated over the arid region in Mongolia using Ulaanbaator Airport radar data from 2003 to 2005. As for the steppe vegetation zone where annual rainfall amount was 100-200 mm, when considerable (little) rainfall was observed in June to July, a positive (negative) NDVI anomaly occurred in July to August and the timing that NDVI reached the maximum was 20-40 days earlier (later) than the 8-year mean. Furthermore, the southern limit of the large rainfall area observed by weather radar corresponded well to the southernmost limit of the positive NDVI anomaly. However, these features were not apparent over the forest steppe vegetation zone where annual rainfall amount was more than 200 mm. It was found that the rainfall distribution obtained by weather radar had a potential for the prediction of the NDVI anomaly and the timing that NDVI reached the maximum over the arid region of Mongolia.