The coastal regions of South Asia, for example Bangladesh, have a long history of cholera outbreaks and are collectively considered the native homeland of the cholera disease since the early 19th century. Cholera incidence data at the International Center for Diarrhoeal Disease Research in Bangladesh (ICDDR,B) is well documented and is perhaps one of the longest and most detailed cholera datasets in the world. Cholera incidence time series in Bengal delta is unique in a sense that it shows two cholera outbreaks in a given season. We hypothesized that spring outbreaks are the results of intrusion of coastal water in Bay of Bengal (BoB) aided through low river discharge while autumn cholera outbreaks are the result of flooding caused by high river discharge. Cholera incidence in this region have been historically linked to environmental and climate variables such as precipitation, floods, river level, sea surface temperature, coastal salinity, dissolved organic material and fecal contamination. The above studies on Bengal Delta cholera dynamics primarily focused on environmental and climatic variables with a single annual peak – and consequently were unable to identify the underlying seasonal processes or drivers behind the dual peaks.

Cholera and Remote Sensing: Almost all major cholera epidemics start in the coastal regions (Figure 1), indicating a strong link between estuarine and riverine water systems and outbreaks of the disease. From initial outbreaks in coastal regions, cholera then spreads to inland areas through river network. Cholera bacteria attach to zooplankton, especially copepods, to form a thin biofilm. Since copepods feed on phytoplankton, a high correlation is expected between copepods and phytoplankton. Consequently, observed abundance in phytoplankton may correspond to an increase in the number of cholera bacteria. The causative agent of cholera outbreaks, V. cholerae, cannot be measured from space. However, the bacteria shows strong affinity with plankton blooms which can be estimated from satellites by measuring chlorophyll present in plankton. Chlorophyll, a key biochemical component that gives plants its green color, is responsible for facilitating absorption of sunlight for photosynthetic purposes. Currently, satellite measured chlorophyll is the only effective way to monitor space-time variations of plankton abundance over large coastal areas. Potentials of using remote sensing data (such as chlorophyll, SST etc) for understanding cholera dynamics across a range of spatial and temporal scales has been highlighted in several studies, however, it is not elaborative on the precise role of remotely sensed variables for understanding cholera dynamics.