• P DINESH KUMAR

      Articles written in Journal of Earth System Science

    • Flood impact assessment using field investigations and post-flood survey

      ALEENA ELSA MATHEW S SUJITH KUMAR G VIVEK M IYYAPPAN R KARTHIKAA P DINESH KUMAR S K DASH G GOPINATH TUNE USHA

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      Kerala, located in the southwest part of India experienced heavy flooding during 2018. A post-flood field survey was conducted by National Centre for Coastal Research (NCCR), Chennai to study the flood. The survey was conducted using in-situ measurement and fed to NCCR-Geo surveyor app. The app is indigenous and transfers the data including flood depth and geo-tagged photos to NCCR server. The survey also focuses on the peoples experience at the time of flood of central and southern parts of Kerala with a total of 206 respondent data. The district-wise survey results are presented. From the study, it was concluded that Pampa River basin and Periyar River basin were severely affected and respondents reported sudden rise in the water levels in locations near to the river banks. Major river banks of the state overflowed and destroyed houses, roads, etc. The field survey points towards long term solutions including advanced flood warning system to create an effective mitigation and preparedness plan to reduce the risk from the fury of future floods and for a resilient community.

      $\bf{Highlights}$

      $\bullet$ The post-flood field survey was conducted for Kerala floods of 2018. A team from NCCR visited the flood affected central and southern parts of Kerala.

      $\bullet$ NCCR Geo-Surveyor app built in-house was used for the survey. A Geo-tagged image together with the flood depth is stored in transferred online into the NCCR server.

      $\bullet$ Presented the district-wise field survey result in the paper. It was noticed that the flood intensified and affected millions due to unscientific way of dam operations, which affected infrastructure and lives of many living on the banks of the river.

      $\bullet$ Kerala need to consider long-term solutions like early flood warning systems, conservation of environment and proper engineered constructions near to the river banks.

    • The impacts of climate change and post bleaching effects on the octocoral communities of Gulf of Mannar, India

      MAHALAKSHMI BOOPATHI P DINESH KUMAR J K PATTERSON EDWARD

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      The objective of the present study is to assess the status of the octocoral communities, and the extent of bleaching they suffered in 2016 (in line with the third Global Bleaching Event). Bleaching survey was carried out in the permanently fixed study sites in the 21 island of Gulf of Mannar. A focused study was carried out in Kariyachalli Island to monitor post-bleaching effects on octocorals. The overall octocoral cover in 2015 was 1.59±0.29%, and octocoral genera such as Sinularia, Sarcophyton, Lobophytum and Subergorgia were observed predominantly in GoM (Gulf of Mannar). Temperature reached a maximum of 32.5°C (March) during 2016 bleaching. The extent of bleaching in 2016 was 1.05±0.65% and the overall octocoral cover was reduced to 1.16±0.22%. Multiple paired t-test results indicate a significant variation in the octocoral covers between 2015 and 2016 (t = 3.173, p${\le}$0.01). Sinularia, Xenia, and Subergorgia were the most affected genera during this bleaching episode. The percentage bleaching in octocorals was the highest in Vembar group of islands (1.9±0.62%) and the continuous monitoring studies reveal the increase in the octocorals diversity from 1.16±0.22% to 1.34±0.21% in 2018 indicating the recovery pattern of octocorals in GoM. Post-bleaching surveys carried out in Kariyachalli Island revealed the occurrence of tissue degradation and algal overgrowth following the bleaching event. However, this study concludes that octocorals in GoM could adapt and Courish in the context of changing climatic conditions. However, more studies on octocoral ecology and biology are warranted.

      $\bf{Highlights}$

      $\bullet$ Percentage cover of the octocorals in Gulf of Mannar was assessed with a total of 16 octocoral genera was recorded during the study.

      $\bullet$ The octocoral cover decreased from 1.59±0.29% (2015) to 1.16±0.22% (2016) and then again increased to 1.34% (2018); with the extent of bleaching of 1.05±0.65% (2016).

      $\bullet$ Sinularia, Xenia and Subergorgia were the most affected genera during this bleaching episode of octocorals.

      $\bullet$ Unusual tulf algal overgrowth with tissue degradation was witnessed in the octocoral genera Sinularia sp.

    • Ocean state forecasting during VSCS Ockhi and a note on what we learned from its characteristics: A forecasting perspective

      R HARIKUMAR P SIRISHA ANURADHA MODI M S GIRISHKUMAR S VISHNU K SRINIVAS RAKHI KUMARI G YATIN P DINESH KUMAR T M BALAKRISHNAN NAIR M MOHAPATRA

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      Tropical Cyclone Ockhi was an intense cyclone, with a peculiar and long track, in the Arabian Sea in 2017. It caused severe damage to coastal infrastructure and death of 282 people. Indian National Centre for Ocean Information Services (INCOIS) issued the Joint INCOIS-IMD (India Meteorological Department) bulletins on the Ocean State Forecasts (OSF) and alerts/warnings during Ockhi. Validation of the OSF from INCOIS using buoys reveals that the forecasts were in good agreement with the observations [average correlation 0.9, RMSE ${\le}$0.8 m (for larger waves), and scatter index ${\le}$25%]. Climatological analysis of Genesis Potential Index (GPI) suggests that the southeast Arabian Sea, where the TC-Ockhi was intensified, had all the favourable conditions for intensification during November/December. Moreover, it was found that four days before the genesis of Ockhi, the environmental vorticity and relative humidity were more favourable for the cyclogenesis compared to vertical wind shear and potential intensity. The intensification rate was rapid as experienced by earlier cyclones in this region. Also, the cyclone track closely matched the background tropospheric winds. The present study suggests that the forecasters should look into the background dynamic and thermodynamic conditions extensively in addition to multi-model guidance to better predict the genesis, intensity and track of the cyclones.

      $\bf{Higlights}$

      $\bullet$ In the Arabian Sea, during the TC-Ockhi, the forecasts of wave parameters from the model forced with bias-corrected ECMWF winds resulted in very good agreement with observations.

      $\bullet$ Climatologically, TC-Ockhi region has large potential for the genesis and intensification of TC due to an enhanced low-level cyclonic vorticity and the reduction in vertical wind shear.

      $\bullet$ During the TC-Ockhi period, low-level vorticity and mid-tropospheric relative humidity were the dominant contributing factors, which lead to an enhanced GPI in the Arabian Sea.

      $\bullet$ TC-Ockhi also had rapid intensification in a similar fashion the earlier cyclones in this region behaved.

      $\bullet$ There is no abnormality also in the TC-Ockhi track, as the TC-Ockhi track matches well with the background tropospheric flow.

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