The phenological pattern of vegetation in Namaqualand, South Africa and its climatic correlates using NOAA-AVHRR NDVI Data

Abstract

Remote sensing techniques were used to reveal the vegetation patterns in the greater Namaqualand area and to relate them to climatic variables. We related the normalised difference vegetation index (NDVI) to a range of different rainfall and temperature indices. Mean annual NDVI is significantly related to precipitation and potential evapotranspiration (PET). A multiple regression model explains 52% of the variance when Mean Annual NDVI is related to climatic variables. Mean NDVI in August (the month of maximum NDVI in most of Namaqualand) is significantly related to PET and the current plus two previous months of precipitation. A multiple regression model for mean NDVI in August and climatic variables explains 57% of the variance. We also assessed the annual and seasonal NDVI pattern exhibited within seven different vegetation types. The climatic variables influencing the summer rainfall and winter rainfall vegetation types differ significantly from each other. All vegetation types have a peak NDVI signal in August although Mountain Fynbos and North Western Mountain Renosterveld values are significantly higher than the rest. Upland, Lowland and Strandveld Succulent Karoo exhibit similar NDVI responses while the two summer rainfall vegetation types (Bushmanland and Orange River Nama Karoo) have a very low NDVI signal throughout the year. The results suggest that NDVI can be used successfully to detect growth and phenology patterns within different vegetation types in Namaqualand.