Delonix regia as a climate bio-indicator: The effect of climate change on flowering time in Kupang, East Nusa Tenggara

Abstract

The study of climate bio-indicators, such as the flowering time of plants, can provide valuable insights into the effects of climate change on the environment. In this study, we investigated the impact of climate change on the flowering time of Delonix regia in Kupang, East Nusa Tenggara. Delonix regia trees at 50 points were observed, and their flowering time was determined in monthly time series between 2013 and 2022 using the Normalized Difference Vegetation Index (NDVI) technique with Landsat 8 satellite imagery. The NDVI criteria for determining flowering were verified through real-time observations during the flowering season in 2021 – 2022 and confirmed using Google Earth imagery. The study’s findings indicate that Delonix regia trees in Kupang previously mass-flowered (> 75% of the population with 65 – 100% closure of the canopy area) once a year in November – December over the past decade, but the flowering time is now changing. Some observed trees in 2021 and 2022 flower twice a year, in April – May and November – December, causing flowering not to close the canopy as in previous years fully. Changes in temperature and rainfall affect the timing of flowering. Increased rain in February-March-April 2021 and 2022 (> 65 mm from the climatology 1990 – 2020) and warmer annual average temperature conditions are thought to trigger flowering initiation, which suggests that climate change significantly impacts the local environment. Our results demonstrate the potential of Delonix regia can be one of the climate bio-indicators and emphasize the importance of monitoring the flowering times of plants.