Torkan 2018 och dess påverkan på skogsvegeationen i Skogaryd och Västra Tunhem, Västra Götaland. - En satellitbaserad fjärranalysstudie

Abstract

In the summer of 2018 Sweden was hit by a long-term drought that heavily affected the forest with forest fires that lasted for several months. After the summer a lot of time and resources were spent on forest fire prevention. However, knowledge is lacking regarding the direct impact of the drought on forest vegetation. The aim of this study is to examine how the drought affected different natural environments in a forest and mire mosaic in SW Sweden. Satellite based remote sensing has been used to produce two Vegetation Indices (VI), namely Normalized Difference Vegetation Index (NDVI) and Normalized Difference Water Index (NDWI), where NDVI measures the photosynthesis and NDWI measures the photosynthesis and wetness of the vegetation. A time series of VI-values over the months of May to September for the years 2017 and 2018 has been constructed over parts of Skogaryd and Västra Tunhem. Climate data has been used for both years to examine the connection between VI, air temperature and precipitation. The remote sensing indicates that the values of both NDVI and NDWI were generally lower during the summer of 2018 in comparison to 2017. However, different trends are visible in different types of vegetation. Both VIs are good indicators of the drought in the deciduous forest and on the mire. NDVI is a good indicator of the drought over the coniferous forest with lower NDVI-values in July 2018. NDWI did not show any clear trends over the coniferous forest. Neither of the VIs from the clear cut show any clear trends. The results from this study indicate that NDVI should be preferred over NDWI as a drought indicator. This is contrary to earlier research that has argued that NDWI is a better indicator of drought than NDVI. The generally lower VI-values for 2018 is most likely a result of the higher air temperatures and lower precipitation in 2018 compared to 2017.