Landfall season is critical to the impact of a cyclone on a monsoon-regulated tropical coastal lagoon

Deepak R Mishra; Abhishek Kumar; Pradipta R Muduli; Tamoghna Acharyya; Prasannajit Acharya; Sambit Singh; Gurdeep Rastogi

doi:10.1016/j.scitotenv.2021.145235

Landfall season is critical to the impact of a cyclone on a monsoon-regulated tropical coastal lagoon

Sci Total Environ. 2021 May 20:770:145235. doi: 10.1016/j.scitotenv.2021.145235. Epub 2021 Jan 20.

Authors

Deepak R Mishra¹, Abhishek Kumar², Pradipta R Muduli³, Tamoghna Acharyya⁴, Prasannajit Acharya³, Sambit Singh⁴, Gurdeep Rastogi³

Affiliations

¹ Department of Geography, University of Georgia, Athens, GA, USA. Electronic address: dmishra@uga.edu.
² Department of Geography, University of Georgia, Athens, GA, USA.
³ Wetland Research and Training Centre, Chilika Development Authority, Balugaon, Odisha, India.
⁴ School of Sustainability, Xavier University, Bhubaneswar, Odisha, India.

PMID: 33513491
DOI: 10.1016/j.scitotenv.2021.145235

Abstract

Cyclones can produce a wide variety of short-term and long-term ecological impacts on coastal lagoons depending on cyclone's physical-meteorological characteristics and the lagoon's geographic, geomorphic, and bathymetric characteristics. Here, we theorized that in monsoon regulated tropical coastal lagoons, another important factor that could determine the impact of a cyclone is the landfall season or time of the year with reference to the monsoon season. We analyzed the impact of two cyclones which made landfall near Chilika, Asia's largest brackish water lagoon in different seasons, Cyclone Fani and Titli before and after the monsoon season. We compared field measured and satellite-derived water quality parameters including nutrient, salinity, water temperature, transparency, Chlorophyll-a (Chl-a), total suspended matter (TSM), and colored dissolved organic matter (CDOM) before and after the cyclones. We found that although both the cyclones were of similar intensities, after their land interaction, their impact on the lagoon's water quality was contrasting. The post-monsoon cyclone produced a substantial increase in total nitrogen (TN) and total phosphorous (TP), a large drop in salinity, CDOM, and Chl-a. In contrast, after the pre-monsoon cyclone, TN and TP did not show any such hike, no substantial change in salinity and CDOM either, and only a slight increase in Chl-a was observed. We found that the controlling factor in determining the impact of a cyclone is the rate and duration of freshwater discharge to the lagoon, which is normally a strong pulse for pre-monsoon and a continued high flow for post-monsoon cyclones. We conclude that the antecedent conditions of the lagoon and the watershed at the time of a cyclone's landfall is a key criterion in determining the impact. The combined use of satellite data and field data was proved critical to capture the overall impact of cyclones on the hydrological characteristics of the monsoon-regulated coastal lagoon.

Keywords: CDOM; Landfall impact; Nutrient dynamics; Remote sensing; Tropical cyclone; Water quality.