Drought identification in the Eastern Baltic region using NDVI

Abstract. The droughts are the phenomena which affect large areas. Remote sensing data covering large territory can be used to assess the droughts' impact and theirs extent. Drought effect on vegetation was determined using Normalized Difference Vegetation Index (NDVI) in the east Baltic Sea region located between 53–60 N and 20–30 E. The effect of precipitation deficit on vegetation in arable land, broad–leaved and coniferous forest was analysed using the Standardized Precipitation Index (SPI) calculated for 1 to 9 month time scales. The vegetation has strong seasonality in the analysed area. The beginning and the end of vegetation season depends on the distance to the Baltic Sea which affects temperature and precipitation patterns. The vegetation season duration in the south-eastern part of the region is 5–6 weeks longer than in the north-western part. The early spring air temperature, snowmelt water storage in the soil and precipitation has the largest influence on NDVI values in the first half of the growing season. The precipitation deficit in the first part of the vegetation season has a significant impact only on the vegetation in the arable land. The vegetation in the forests is less sensitive to moisture deficit. The positive correlation between 3 and 6 month SPI and vegetation condition was observed in the arable land and both types of forests in the second half of the vegetation season. The precipitation deficit is only one of the vegetation condition drivers and NDVI cannot be used universally to identify droughts, but it may be applied to better assess the effect of droughts on vegetation in the eastern Baltic Sea region.