Long-term changes of surface albedo and vegetation indices in north of Iran

Abstract

Surface albedo is a key parameter in earth energy budget and global climate change studies. In this aspect, variation in vegetation covers is one of the most critical issues affecting global energy balance. The present study is conducted to examine the relationship between changes in vegetation cover (by using NDVI and EVI indices) and changes in surface albedo. Using qualified MODIS data, mean annual albedo variations (during the growing season) and their relation with the changes in NDVI and EVI values in 6 climate zones are investigated for the period of 2004 to 2016. The results show that the lowest variations of albedo are observed in the region with SH-C-VW climate and the highest in the SA-C-W climate. With the exception of A-C-W and SA-C-W climates, the absolute value of the Pearson correlation coefficient between albedo and EVI is stronger than NDVI. Hot spots of temperature and precipitation are detected by employing daily measurements of 17 weather stations to find the relationship with the changes in surface albedo. According to the results, surface albedo has increased during the study period in majority of the weather sites. Generally, increase in surface albedo was evident for 61% of the study area, while decreases were detected in 30% and no significant changes in the remaining areas. Also, except for SH-C-VW climate, albedo has experienced an increasing trend in all climates from April to September. The major albedo declines are found in the Hyrcanian forests, where higher vegetation cover is confirmed by Iran Forests, Range and Watershed Management National Organization. Examining the hot spots in temperature and precipitation reveals that the reduction of albedo (due to the increase in vegetation cover) in the areas coincides with more rainfall in the region. In contrast, higher temperatures were observed for areas with the decreased vegetation cover.