State's sea levels may rise by 0.38 metre by 2050

Few decades on, structures near Mumbai's seashores may be inundated by rising sea levels. In what may drastically alter perceptions about climate change and its impact on coastal cities like Mumbai, a state government study has predicted a 0.38 metre rise in sea levels across Maharashtra by 2050.

The Maharashtra Maritime Board's (MMB) shoreline management plan (SMP) has suggested that construction near the coast in Mumbai must rise to a minimum 7.59 metres above mean sea levels by 2050 to withstand storm surges and floods. While Coastal Regulation Zone (CRZ) notifications regulate a 500 metre horizontal region from the high-tide line, the SMP lays down a vertical impact of the sea-level rise. This can be incorporated into urban and land use planning, serving as baseline data for planners executing shoreline infrastructure projects like Mumbai's coastal road.

"This is Maharashtra's first SMP. Developed countries like Singapore and Australia have SMPs and consider them as reference points in coastal planning," explained Jitendra Raisinghani, Deputy Director, Co-Ordination, Asian Development Bank project, MMB.

The MMB will circulate the SMP to state and central agencies, local bodies like BMC and district authorities.

"The maximum reported tidal level in Mumbai is 2.83 metres above mean sea level. This means by 2050, another 0.38 metres is estimated to be added to it during high-tides due to sea-level rise," explained a source. Sea-levels are estimated to rise by a uniform 0.38 metres across Maharashtra's 720-km coast.

The SMP predicts a maximum possible storm surge of 2.09 metres above prevailing sea levels for Mumbai, which will be a "freak event" but must be considered while planning major projects.

"The southern parts of Maharashtra's coast in Ratnagiri and Sindhudurg have rocky cliffs to mitigate the sea-level rise. However, in the northern part, including Mumbai, it may cause inundation," he said, stressing on the need to consider the SMP in urban and developmental planning.

Construction standards will have to be based on the area, survey maps and height of the location from the mean sea level. The plan has been finalised after visiting all 103 beaches in the seven coastal districts. It is based on GIS maps and factors like Bathymetry, geo-morphic conditions, computer simulatuions about the climate change scenario, land use, sand quality, gradient of beaches into the sea, sea rise projections and wave impact for the next 50 and 100 years. Sea level changes, coupled with storm surges and increase in the magnitude of tropical cyclones will pose a risk to coastal cities.

Mumbai has seven beaches, namely, Girgaum Chowpatty, Priyadarshani Park, Dadar, Juhu, Versova, Aksa and Gorai.

Raisinghani said around 90 per cent of Maharashtra's beaches will be stable as they were sheltered. The around Rs 648 crore Sustainable Coastal Protection and Management Investment Programme (SCPMIP) is being implemented at 11 vulnerable coastal sites to protect the coastal ecosystem and check erosion and accretion. The SMP needs to be updated on a five-year time scale. Experts note that dams and sand mining in rivers affect supply of new sand to beaches and cause erosion.