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

Abstract

Through an analysis of land use and land cover (LULC) data for the years 2005 and 2017 from the Advanced Wide Field Sensor onboard the Indian Remote Sensing satellite, we find considerable changes in the LULC in three major states of south India, namely, Tamil Nadu, Telangana and Kerala. This change is mainly due to increasing urbanization, in addition to the change of prevalent mixed forest into deciduous needle/leaf forest in Kerala. Motivated by this finding, we study the impact of these LULC changes over a decade on the extremes of twelve heavy rainfall events in these states through several sensitivity experiments with a convection‐permitting Weather Research and Forecasting model, by changing the LULC boundary conditions. We particularly focus on three representative heavy rainfall events, specifically, over (a) Chennai (1 December 2015), (b) Telangana (24 September 2016), and (c) Kerala (15 August 2018). The simulated rainfall patterns of the three heavy rainfall events are found to be relatively better with the use of the 2017 LULC boundary conditions. The improvement is statistically significant in the case of the Chennai and Kerala events. On analysis of these simulations, and output from additional simulations we have conducted for nine other heavy rainfall events, we suggest that the recent LULC changes result in higher surface temperatures and sensible heat fluxes, and a deeper and moist boundary layer. This causes a relatively higher convective available potential energy and, consequently, heavier rainfall. We find the LULC changes in the three states, mainly dominated by the increasing urbanization in Telangana and Tamil Nadu, enhance the rainfall during the heavy rainfall events by 20–25%. This is the first extensive investigation of multiple and multi‐regional cases over the Indian region.

Impacts of Urbanization, Aerodynamic Roughness, and Land Surface Processes on the Extreme Heavy Rainfall Over Chennai, India

“…Previous studies suggested that the moisture transport from BOB and its convergence under the persistent synoptic low‐pressure trough caused the heavy rainfall (Chakraborty, 2016; Narasimhan et al., 2016; Srinivas et al., 2018). Also the recent studies (Boyaj et al., 2020) on urban impacts on Chennai heavy rainfall emphasized the role of enhanced thermal transport and ignored the role of urban‐induced roughness and the associated physical processes in the simulations.…”

“…A few studies analyzed the consequences of urban expansion and induced land use changes on extreme rainfall scenarios over tropical Indian cities (Boyaj et al, 2020;Kishtawal et al, 2010;Mohan & Kandya, 2015;Paul et al, 2018). Kumar et al (2008) showed that the highly localized heavy rainfall event (August 2005) over Mumbai was produced as a result of the interaction of synoptic-scale low-pressure system with the typical mesoscale land surface features of this region.…”

The Importance of the Orbital Parameters for the Indian Summer Monsoon During the Mid-Holocene, as Deciphered From Atmospheric Model Experiments

“…Any changes in the average seasonal rainfall patterns have a profound effect on agriculture, and therefore the livelihood of 1.5 billion people in South Asia (Gadgil and Rupa Kumar, 2006). The Indian summer monsoon rainfall (ISMR) is weakening over several regions (e.g., Krishnan et al, 2020), with a simultaneous increase in the extreme events in the recent ∼150 years (Boyaj et al, 2020, and the references therein). Observation-based studies in the last 50-100 years suggest that, on interannual time scales, tropical oceanic phenomena such as the ENSO dominantly influence the ISM variability (see Webster et al, 1998, and the recent reviews by Ashok et al, 2019;Mohanty et al, 2020, and the references therein).…”

The Anomalous Weather Parameters that Lead to the Extreme Rainfall of Kerala in August 2018

“…The extreme weather event during August 2018 in Kerala was attributed to anomalous weather conditions rather than the warming trend in the atmosphere by . Modi cations in the land cover resulted in higher surface temperatures, sensible heat ux, and a deeper and moist boundary layer, resulting in heavy precipitation (Boyaj et al 2020). According to Viswanadhapalli et al ( 2019), high convective instability, offshore vortex, moisture transport from mid-troposphere due to horizontal wind shear and mid-tropospheric moisture transport from the Bay of Bengal played major roles in the extreme precipitation event.…”