Climate, trends and variability of extreme winds along the southwest coast of India

Abstract

The extreme wind climate and its trends and variability of the southwest coast of India, particularly the Kerala coast, are investigated using hourly reanalysis wind speeds for the period 1979–2021. The observed maximum wind speed and 99th percentile wind speed off Kerala coast are 21.0 and 11.3 m·s−1, respectively. The predominant direction of high wind speeds is in the SW–WNW sector, which accounts for 93.5% of the total high winds. Extreme wind speeds in this region are not due to tropical cyclones alone, but also due to seasonal high winds. Seasonally, the premonsoon and SW monsoon extreme winds are predominantly in the WSW–WNW directional sector, while postmonsoon strong winds are present in all directional sectors, but predominantly in the SSW–WNW sector, followed by the E–SSE sector. The 99th percentile wind speeds during premonsoon, SW monsoon and postmonsoon are 8.8, 12.3 and 8.9 m·s−1, respectively. A significant decreasing trend is observed in the 99th percentile wind speeds during 1979–2021, ranging from 3 to 6 cm·s−1·year−1 off Kerala coast. This is in contrast with global increasing extreme wind speeds, and it can be attributed to regional variability as well as weakening of the land–sea thermal gradients associated with rising surface temperature in the Arabian Sea in the light of global warming. In addition to the long-term declining trend and monthly as well as seasonal features, distinct interannual variations are also noticed in the 99th percentile wind speeds. Analysis shows that the atmospheric teleconnections associated with El Niño–La Niña events and Indian Ocean Dipole have an important role in the variability of extreme wind speeds. The co-occurrence of positive (negative) IOD with El Niño (La Niña) results in a sharp decline (increase) in extreme wind speeds. Significant decadal variations are also noticed in the 99th percentile wind speeds.