The Mahanadi delta in Odisha is a composite delta fed by water, sediments and nutrients from a network of three major rivers: Mahanadi, Brahmani and Baitarini. The coastline of the delta is approximately 200 km long, extending from the Chilika lagoon in the south to the Dhamara river in the north. It has five coastal districts - Puri, Khordha, Jagatsinghpur, Kendrapara and Bhadrak which constitute 83% of the delta area and have large areas below the five metre contour where floods due to cyclones and sea-level rise are common.
A research study ‘The Mahanadi delta: A rapidly developing delta in India’ looked at the changes in the Mahanadi catchment basin since the onset of the Anthropocene (i.e., since 1950). It focused on the evolution of the Mahanadi delta, both in terms of biophysical and socio-ecological change over time including delta management and policy evolution.
Post 1950, the growth rate of the delta declined significantly, in line with a period of intense dam building. This started with the construction of the multipurpose Hirakud dam on the Mahanadi river near Sambalpur in 1957, and has resulted in a total of 254 mainly small and medium scale dams within the drainage basin.
The once prograding delta that was advancing towards the sea as a result of the accumulation of waterborne sediment is retreating since 1950s. The reasons include: sediment starvation, sea-level rise, experiencing accelerated population growth, decline in income from agriculture or fisheries, increasing pollution in the river system with potential of acidification of estuaries, proliferation of plastics in the environment, degradation of mangroves with loss of biodiversity and human migration.
Major challenges in the Mahanadi delta
- Restoring or maintaining the natural delta dynamics to combat the cumulative threat of sea-level rise and land subsidence is a challenge. There is a need to address the water-sediment-pollution-biodiversity interactions, while maintaining the socio-economy of the delta in an integrated and inclusive way to make the delta sustainable for the future generations. The interactions of the rural delta areas with the urban delta areas also need to be considered.
- Since the 1950s, the coastal districts of the delta have also witnessed rapid increase in population (especially Bhubaneswar city), growth of a port, industrial development along with increased groundwater extraction, small- and medium-scale irrigation projects and deforestation of mangroves. The Mahanadi river system has experienced a substantial increase in the amount of untreated sewage and industrial effluent and rising levels of pollution.
- More than 57% of the land area of the Mahanadi delta is under cultivation, with a subsidiary occupation of capture and culture fisheries, provides the subsistence for the predominantly rural population of the delta. The rapid urbanisation and development in agricultural practice over recent decades have left a mark on the environment. Land use analysis finds that between 2001 and 2011 alone, the delta has lost 4600 hectares of agriculture land and 360 hectares of pristine mangrove forest to urban/rural settlements and aquaculture.
- The delta is now shrinking and a more challenging situation is emerging. The most vulnerable communities often suffer disproportionately at times of natural disasters with potential loss of life, livelihoods and assets.
- The decline in sediment supply has been significant, amounting to 67% for the Mahanadi river and around 75% for the Bramhani river. As a consequence, over 65% of the coastal margin is presently experiencing moderate to severe erosion, with increasing rates from south to north. For example, between 1990 and 2015, the shoreline (as mapped in 1950) receded at a rate often exceeding 10–15 m/year. Near the Mahanadi estuary, the rate has exceeded 50 m/year. Hence, erosion is now a key feature of the once prograding delta.
Extreme events and climate change
Climatic extremes have a potential to affect the delta adversely. The Mahanadi delta is situated in the most cyclone-prone region of India. Historical data on cyclones in Odisha indicate high disaster losses due to cyclone and surges in the Anthropocene period with eight high-intensity flooding events reported during the period 2001–2015.
Future climate data from regional modelling also indicates that precipitation along with high rainfall events may increase significantly in the later part of this century. The greatest impact of these high discharge events and flooding would be on agricultural land along with a number of urban areas across the delta. In addition, the rate of relative sea-level rise in the last decade has increased to nearly 6 mm/year.
Future projections under a business as usual scenario are not encouraging for the Mahanadi delta. Higher sea surface temperatures (a rise of potentially 2.3–2.9 °C and sea levels along with an increasing number of high rainfall events, particularly in the later part of the century, has a potential for increased number of flood events endangering life and livelihoods of the delta community.
Climate change and climatic shocks also have the potential to reduce crop yield in the delta. It is estimated that by 2050, the economic loss from agriculture could be about 5% of GDP per capita. However if loss of infrastructure is considered, climate change and climatic shocks (flood, cyclone, etc.) may lead to cumulative per cent loss in GDP per capita of about 11% in the delta. At the same time, with the projected loss of fisheries production, the socio-economic integrated model indicates that losses from the fishery sector alone to be around 0.25% of the total GDP in the delta by 2050. These together impose a serious constraint on the livelihood of the delta community in future.
65% of the deltaic coast is also currently experiencing varying degree of erosion, a situation which is expected to worsen by 2050, implying compounded threat to the coastal habitations particularly between Puri to Paradip and promoting increased out-migration of people from the coast.
This research has the following three key observations for the Mahanadi delta:
- Assessing the Mahanadi Delta region as a unit of planning and implementation offers opportunities to enable coherent policy responses to reduce the risk of climate change to populations by supporting gender-sensitive adaptations;
- The most practiced adaptation activities are not always the most successful in the Mahanadi delta. Adaptation activities are not always gender-sensitive with the effect that men are benefiting more than women. Thus, it has to be ensured that the most vulnerable groups including the elderly, the severely poor, the physically challenged and women are involved in the development of migration-related adaptation as stakeholders. So, a variety of types of adaptations should be used to reduce climate change risk; and
- To encourage migration as an adaptation, targeting trapped populations with skill development (as observed in Pattamundai, Kendrapara district) can improve their migration capability. Alternatively, designing income-generating opportunities like skills training, livelihood programmes and development initiatives for those who remain behind in areas affected by disasters/climate change will reduce their vulnerability and increase their ability to cope during an extreme weather event.
The full study can be accessed here