A diagnostic study of extreme precipitation over Kerala during August 2018

Abstract

The state of Kerala, located on the west coast of India, experienced a record 100‐year flood that resulted in major landslides from unprecedented prolonged and extremely heavy rainfall (50–480 mm·day−1) during August 1–19, 2018, causing extensive damage and about 500 causalities. Rainfall observations indicate that the heavy rainfall occurred over two spells (August 7–10 and 14–18) in association with an offshore trough, and a depression over the Bay of Bengal (BOB). High‐resolution 38‐year climatology data (5 km) and the ERA‐Interim reanalysis dataset show a strong low‐level jet over the Arabian Sea and a depression over the BOB with a southwestward tilt during the heavy rainfall. Very high‐resolution (2‐km) mesoscale model simulations suggest that this high convective instability due to the strong westerly jet along with the formation of offshore vortex, the transport of mid‐tropospheric moisture under the presence of conducive vertical shear of horizontal wind, and transport of mid‐tropospheric moisture from the BOB are the major factors (as shown in the schematic diagram) behind the extreme heavy rainfall over Kerala.

Increasing heavy rainfall events in south India due to changing land use and land cover

“…Of late, several heavy rainfall events have been reported in these states (e.g. Srinivas et al ., 2018; Viswanadhapalli et al ., 2019). Interestingly, one common factor across these states is an apparent urbanization as implied by the increasing industrial activity and migration to cities.…”

“…The Weather Research and Forecasting (WRF) model version 3.8.1 (Skamarock et al ., 2008), which is a mesoscale numerical weather prediction system designed for atmospheric research and operational forecasting needs, is employed in this study. The WRF model predictability of heavy rainfall events over the Indian region has been ascertained in several studies (Sahany et al ., 2010; Hariprasad et al ., 2011; Bhanu Kumar et al ., 2012; Chawla et al ., 2018; Srinivas et al ., 2018; Viswanadhapalli et al ., 2019). For this study, the model has been configured with three two‐way interactive nested domains with horizontal outer‐to‐inner resolutions of 18, 6 and 2 km.…”

“…A detailed diagnostic study of this event was carried out by Viswanadhapalli et al . (2019) through an analysis of observations and high‐resolution WRF model simulations. The present study states that several major factors, specifically, a strong monsoon flow along with the formation of an offshore vortex, a transport of mid‐tropospheric moisture from the Arabian Sea, and a convective low vertical shear of horizontal wind were instrumental for the heavy rainfall.…”

Assessment of WRF Model Parameter Sensitivity for High‐Intensity Precipitation Events During the Indian Summer Monsoon

“…Viswanadhapalli et al. (2019), Baisya and Pattnaik (2019), and Chakraborty et al. (2021) simulated the Kerala heavy rainfall event during 2018 and identified strong westerly jet, the transport of mid‐tropospheric moisture, and the horizontal moisture flux convergence as the critical drivers of convection.…”

Flood inundation mapping- Kerala 2018; Harnessing the power of SAR, automatic threshold detection method and Google Earth Engine

“…The extreme precipitation and runoff conditions observations made by Mishra et al using the Variable Infiltration Capacity (VIC) model, have shown that the 2018 extreme flood event was unprecedented in the last seven decades from 1951-2018 [33]. The simulation results by Viswanadhapalli et al, suggested that the high convective instability and transport of mid-tropospheric moisture from the Bay of Bengal were the driving factors behind the heavy rainfall over Kerala in 2018 [34]. The change in water levels of reservoir storage during extreme rainfall of Kerala in 2018 were also discussed by Ramasamy et al, Anandalekshmi et al,.…”