Assessing Effect of Droughts and Heatwaves on Indian Tropical Forests using Time-Series Meteorological and Vegetation Biophysical Parameters

Abstract. Heat waves and droughts are recurring global phenomena that profoundly influence terrestrial ecosystems. This study assessed the impacts of drought and heat waves on the functioning of tropical evergreen (Kerela, South India) and moist deciduous (Barkot, North India) forest sites using meteorological and satellite vegetation products, including the FAPAR, SIF, GPP, and ET during 2007– 2018. The SPI, calculated from ERA5 daily data, was used to identify drought occurrences in space and time, while the Mann–Kendall test detected historical trends. Heat waves were characterized using hourly maximum temperature data from ERA5, following the criteria of IMD. Temporal anomalies were quantified using Z-scores, along with the Mann–Kendall trend test and Theil–Sen’s slope analysis. Moist deciduous showed consistent and pronounced declines in productivity and moisture related variables during droughts, particularly during monsoon season, indicating strong sensitivity to water stress. Evergreen forests exhibited more variable responses, with weaker and less consistent drought signals during the pre-monsoon season and mixed responses in vegetation variables even during monsoon drought conditions. Heat wave impacts also varied across forest types. Evergreen forests showed contrasting responses depending on the timing of heatwave events, with early and mid-heatwave phases associated with reductions in productivity, while late heatwave events showed relatively positive or mixed responses among vegetation indicators. In moist deciduous, heatwaves resulted in more consistent negative anomalies in productivity-related variables, although some years exhibited contrasting behaviour in SIF relative to other indicators. The findings underscore the heterogeneous response of forest ecosystems to extreme climatic events.