Satellite study identifies critical impacts of coastal inundation along Mumbai Metropolitan Region
While there are several projections of sea-level rise along the Mumbai and Maharashtra coast leading up-to 2030, a latest study assessing satellite data over 30 years (1990 and 2019) has already begun identifying critical impacts of coastal inundation along Mumbai Metropolitan Region (MMR) and Konkan region.
As per a study undertaken by Srushti Conservation Foundation (SCF) - a Pune based non-profit organisation, siltation at the mouth, causing shrinking width of creeks and waterways along MMR including Mumbai, Thane, Navi Mumbai, Uran among others. Further the volume of water in the estuary between high tide and low tide (tidal prism) during non-monsoon months is altered due to land use changes, and is putting many coastal townships in the MMR at risk of increased inundation especially during monsoon months.
Preliminary findings of this study indicate that a total area of 107.6 square kilometres (a little over the size of the Sanjay Gandhi National Park - 103 square kilometres) of waterways and agricultural land has been lost and naturally converted into mudflats or mangrove areas in MMR due to rapid changes in the coastal ecosystem over the last 30 years.
Rising Sea…Shrinking creek
Dr Deepak Apte, Executive Director of Srushti Conservation Foundation (SCF) stated that without policy and on site interventions, such creek areas will overtime be converted into mangrove forests, extremely shallow swamps or even dry lands in many parts, which will become unfit for navigation, reduce storm water drainage capacity, and will render the habitats unsuitable. It will especially affect the flamingo habitat in areas like Thane Creek, he said.
The report predicts the possibility of excessive flooding in MMR if corrective measures are not taken. “The shrinking creek is not good for a city because the drainage capacity during monsoon will reduce significantly leading to excessive flooding for this region. Once it becomes shallow the water carrying capacity of the creek will be reduced. As a result, during heavy rains and high tide water will enter the city spaces even with a subtle increase in sea level rise scenario,” said Apte.
Apte informs that sea level rise leading to coastal inundation is a reality, which will affect millions of coastal populations causing loss of livelihood, land degradation etc. He recommends building resilience of coastal communities, promoting nature based solutions, and preparing them for mitigating climate- related risks to be of paramount importance for the resilience of the city.
The National Centre for Coastal Research (NCCR) under the Ministry of Earth Sciences along with the Municipal Corporation of Greater Mumbai last year developed an Integrated Flood warning system called i-flows for Mumbai for flood mitigation during monsoons and extreme events. “The expertise of NCCR could be utilised for drawing a comprehensive plan for conservation /restoration ecosystem
using scientific study and also to prevent the impact of sea-level rise, which is of serious concern for the island city of Mumbai and adjoining areas,” said Apte.
Cases Studies in MMR
SCF is building satellite datasets for 15-20 locations across the Maharashtra coastline working over this year to bring out a comprehensive report to aid policymakers on the issue of coastal inundation and land degradation. Incursion of saline water and emergence of mangroves on agricultural (paddy
fields) landscapes for example in Karanja area of Uran has led to a 4.5-fold increase in mangrove area by formation of creek-lets and saltwater invasion across 60.6 sq. km of cultivable area replaced by mangroves. Similarly, approximately 47 sq. km of waterways were replaced along Mumbai- Thane creek by land (mangrove/mudflats, etc.) with 24 sq. km alone along Thane Creek. This was a result of accumulation (of silt), land reclamation, reduction in freshwater during non-monsoonal time and consequent impacts of rising seas. The case is the same for other creeks along this megacity (MMR), the study said.
Choking creeks, excessive mangrove growth may cause flamingos to permanently move away
The analysis revealed that surface waters across Mumbai and Thane creeks along the eastern seafront witnessed a steep decline from close to 400 sq. km in 1990 to over 350 sq. km by 2019. At the same time, average flamingo numbers gradually increased from a few thousand to 20,000 between 1995 to 2005 and then shot up, touching 1,20,000 by 2019 as seen through various media releases of the Bombay Natural History Society.
“Flamingos and migratory waders are presently benefiting from the shrinking waterways as their population increase is being witnessed in the same trajectory as the expansion of mudflats and mangroves. This in combination with high sewage load that MMR is pumping into the creek as well as warm water from refineries and power plants make it a perfect feeding ground (with nutrient rich flora and fauna),” said Apte.
Another factor that is aiding such high abundance especially in Thane Creek is loss of wetlands in MMR and Uran region as reported by Bombay Natural History Society that is squeezing these birds in relatively safe Thane Creek, added Apte. However, once the accreted land is taken over by mangroves in combination with reduction in tidal prism during non-monsoon months, soft mudflats turn into hard and barren land. “Thus, flamingos will permanently move away from such habitats,” he said.
Impact on agricultural lands and livelihoods
The study revealed there was another issue pertaining to kharland bunds. Along coastal zones, most of the agricultural lands along the banks of estuaries or near the sea are slowly being converted to saline land also called kharlands.
In the case of Karanja in Uran, the satellite data revealed that while mangrove area increased from just 17.5 sq. km in 1990 to 78.1 sq. km in 2019, a parallel decline in agricultural land saw reduction of 17.8 sq. km in 1995 and 60.6 sq. km by 2019. “The issue has to be addressed as we are fast losing these agricultural areas to changing climatic conditions, and building kharland bunds is not the long term solution as the height of these bunds have to be increased keeping with the pace of sea level rise and coastal inundation,” said Apte adding that these bunds not only kill mangroves that work as shore protectors but also cause livelihood loss for the coastal fishing community.