Decadal Climate Variability and Its Impact on Mangrove Ecosystems of the Southwestern Coast, India

The mangrove ecosystem, a wetland forest found in tropical and subtropical coastal regions, is influenced by key factors such as tide height, salinity, precipitation, and temperature. This study focuses on understanding the impact of these factor’s decadal changes on three mangrove vegetation patches (Kozhikode, Ernakulam, and Kollam) on the southwestern coast of India. For this study, the recent past (2012-2022) rainfall and temperature data from the Indian Meteorological Department (IMD) and tide height data collected from INCOIS were used. Land surface temperature (LST) data based on MODIS and Enhanced Vegetation Index (EVI) and Salinity Index (SI) based on Landsat 8 were extracted using Google Earth Engine. The average annual rainfall at Kozhikode, Ernakulam and Kollam are 2934 mm, 3082 mm and 2305 mm, respectively.  The land surface temperature has an almost similar seasonal trend across all three mangrove sites, varying between 25 °C  to 31 °C in different seasons. The annual average tide height is observed to be highest at Kozhikode (0.97 m) and lowest in Kollam (0.49 m), whereas the annual average SI is observed to be highest in Kochi (0.13) and lowest in Kozhikode (0.10).

Evaluating vegetation changes using the EVI is essential for assessing the system’s effectiveness in protecting coastal areas from floods and guiding the planning of restoration and protective measures. The correlation coefficient between EVI and other climate variables was used to understand its impact on vegetation. Salinity, monsoon rainfall and summer LST are observed to be negatively correlated with the EVI in all three study areas. In contrast, during the southwest monsoon season, the tide height and LST positively correlate with EVI. This study revealed that optimum rainfall, salinity, and LST conditions are favourable for its growth, beyond which it negatively impacts vegetation compared to the rise in the tide height.