**1. Introduction**

The Sundarbans, the world's largest coastal river delta and the largest uninterrupted mangrove forest, is critical biodiversity and climate hotspot [1]. It has a complex ecosystem studded with inter-tidal and estuarine zones stretching for about 10,000 km<sup>2</sup> and is located on the borders of the state of West Bengal in India (~40%) and southern Bangladesh (~60%) where the Ganges, Brahmaputra, and Meghna rivers meet the Bay of Bengal. Coastal river deltas are often naturally low-lying areas close to the local mean sea-level. Changes in regional sea-levels a ffect coastal river delta systems geomorphologically by altering the base level, coastal erosion, and inundation, not to mention inland propagation of tidal and backwater e ffects [2,3]. The geomorphological response of a coastal river delta system to sea-level rise is determined by the delta system's capacity to adapt. The system is complex owing to the variety of feedbacks and changes in internal and external boundary conditions, including sediment supply, river discharge, ecological system feedbacks, subsidence, and human intervention; it is also mainly associated with hydrodynamic and ecological responses [2,4]. It influences system functioning and determines the ability to either adapt dynamically, mitigate the e ffects of regional

sea-level, or submerge [5,6]. In the coming decades, the e ffects of human intervention, causing further subsidence, changes in sediment supply, river discharge, and ecosystems will be dominant in determining the impacts of sea-level change in coastal river deltas [5,6].

The coastal regions of the Bay of Bengal, especially the Sundarbans delta, are among the most vulnerable areas of the world in terms of experiencing the rapid sea-level rise, seawater intrusion, and other climate change impacts [7,8]. The Sundarbans landscape is highly fragile and particularly vulnerable to global and regional climate change impacts because of its complex geomorphology and environmental settings attributable to continuing global warming, rising sea-levels, seawater intrusion, land erosion, gradual subsidence, and cyclones [1,9,10]. The Sundarbans' mangroves, which protect more than 10 million people from cyclonic storms, today stand threatened by cyclonic damage. Cyclones and tidal storm surges cause damage to the floral and faunal biodiversity along the sea-land interface [1].

The sea-level has risen approximately three to four times higher than the global mean between 1993 and 2009 in the tropical western Pacific and the Indian Ocean [11]. The coastal region in the southwest of Bangladesh has undergone a relative sea-level rise varying from 2.8 to 8.8 mm per year in the last few decades. In South Asia, the sea-level in the Ganges-Brahmaputra-Meghna delta of Bangladesh is likely to rise by 0.63 to 0.88 m by 2090 [12]. Frequent cyclones, together with increasing sea-levels, have resulted in flooding, coastal erosion, and recession of coastline in the region [13].

Coastal flooding is driven by multiple factors, including local land elevation, regional sea-level rise, heavy precipitation, tidal waves, storm surges, and tropical cyclones [14–18]. All these factors are likely to adversely a ffect the lives and livelihoods of the local community.

The remaining part of the paper describes the study area and sampling; it discusses the methodology adopted for climate change modelling, construction of fuzzy cognitive maps, and fuzzy cognitive map-based simulations. After this, we present the results of climate change projections. We describe the climate change impacts and adaptations as perceived by the community before presenting the results of fuzzy cognitive maps (FCM)-based simulations. Finally, we discuss the results in detail, drawing appropriate conclusions. The paper ends with guidance for future research.

#### *Study Area and Sampling*

The Indian Sundarbans, comprising 54 islands, is home to about 4.5 million people [19]. An analysis of the SRTM data reveals that these islands are naturally flat, mostly comprising moderately elevated areas (0 to 5 m high from the mean sea-level), with few low-lying and elevated regions (0 m and 5 to 10 m respectively).

Agriculture and fishing are the two major livelihood options available to the communities living in this region. However, both sectors have been facing stress due to seawater intrusion, coastal erosion, and the increasing salinity in agricultural fields and river water. All of this has been causing a sizeable male population to emigrate from the villages. Phenomena like global and regional climatic changes coupled with anthropogenic pressures including poaching, human encroachment for agriculture and fishing, and overexploitation of both timber and non-timber forest produce have led to multiple alterations in the mangrove flora, fauna, and ecosystem dynamics and functions posing, as a consequence, severe threats to the Sundarbans' ecosystem [9]. They also introduce many changes in the ecosystem services vital for human health, wellbeing, and livelihoods [1,9,20].

This perception mapping study engaged 46 community groups (male and female groups constituted 35 and 11 respectively) from seven villages in Sagar and Mousini islands of the South 24 Paraganas district of Sunderbans.
