Interannual variability of monsoon onset and withdrawal in Bangladesh

Abstract

This research investigates the interannual variability of monsoon onset and withdrawal in Bangladesh, both of which are major climate features shaping multiple societal activities. There is considerable research on the monsoon timing in South Asia, but with much less focus on Bangladesh. We applied a local monsoon onset and withdrawal definition to observations and the latest-generation high-resolution gridded precipitation data from the Climate Hazards Center for the period 1981 through 2018. We analyzed the interannual variability in monsoon timing in Bangladesh and its teleconnection with the sea surface temperature anomalies (SSTA) over the Pacific Ocean (El Niño Southern Oscillation, ENSO) and the Indian Ocean (IO). The monsoon starts with early significant rains in northeast Bangladesh and propagates westward, and a similar pattern is observed for withdrawal, which tends to be more homogeneous in time and space. A high spatial and temporal variability in monsoon onset and withdrawal is observed in Bangladesh, with a within-country average range of around 1 month despite it being a country of relatively small size. The association between monsoon onset and withdrawal and ENSO and IO is addressed at the country and regional level by analyzing composites for different ENSO and IO phases and associated atmospheric circulation and moisture transport. A similar association between monsoon onset and ENSO and IO phases was found, with generally earlier (later) onset dates during the negative (positive) phase of ENSO and IO. Monsoon withdrawal shows a clearer association with ENSO, with earlier (later) dates during the positive (negative) phase. Monsoon withdrawal is earlier during the negative IO phase. SSTA-induced anomalies in circulation and moisture transport contribute to anomalies in monsoon timing. Results suggest both ENSO and IOD can be potentially used as sources of predictability of monsoon onset and withdrawal over specific regions of Bangladesh.

Agronomic monsoon onset definitions to support planting decisions for rainfed rice in Bangladesh

“…The dates obtained by Dynamic 2 vary from May 30 th in Dinajpur to June 6 th in Rajshahi. These mean values and range of interannual variability agree with previous studies (Ahmed and Karmakar 1993 ; Montes et al 2021b ; Stiller-Reeve et al 2014 ), as well as the spatial pattern of later onset dates over Rajshahi and earlier over Barishal and Dinajpur. The time series of onset dates also indicate a relatively high interannual variability obtained by both methods, with a standard deviation ranging from 10 to 15 days.…”

“…The four weather stations were selected according to the availability of data necessary for both the implementation of the monsoon onset method and crop modeling. Despite the limited number of locations, they can represent an early to late gradient of monsoon onset (Montes et al 2021b ). Daily rainfall, minimum and maximum air temperature, sunshine hours, relative humidity and wind speed data for the period 1981-2017 were provided by the Bangladesh Meteorological Department (BMD).…”

“…Information on the timing of the monsoon onset is crucial for livelihoods in Bangladesh, driving the decision-making of multiple stakeholders. The climate science community has made long-standing efforts to better understand the physical mechanisms of monsoon development and progression and, eventually, to advance in the predictions of monsoon timing in Bangladesh (Montes et al 2021b ). However, there have been historical 'usability gaps' between the knowledge producers (i.e., National Meteorological Services) and the actual users (i.e., extension workers or farmers in the case of agriculture) from the perspective of climate services (Lemos et al 2012 ; Raaphorst et al 2020 ).…”

Planting Rice at Monsoon Onset Could Mitigate the Impact of Temperature Stress on Rice–Wheat Systems of Bihar, India

“…These definitions vary from local to regional, in which the variables considered may be rainfall, wind direction, or atmospheric circulation [30]. Previous studies have used and compared monsoon onset definitions in South Asia and over the Eastern IGP, describing the main features in the regional monsoon timing patterns and variability [31][32][33]. In this work, the local agronomic onset definition of Marteau et al [34] was used, which was developed for agricultural applications.…”

Planting <em>Aman</em> Rice at Monsoon Onset Could Mitigate the Impact of Temperature Stress on Rice-Wheat Systems of Bihar, India

“…These definitions vary from local to regional, in which the variables considered to define the onset of the monsoon may be rainfall, wind direction, or other variables associated with atmospheric circulation [32]. Previous studies have used and compared monsoon onset definitions in South Asia and over the Eastern IGP, describing the main features in the regional monsoon timing patterns and variability [33,34,35]. In this work, the local agronomic onset definition of Marteau et al [36] was used, which was developed with a focus on agricultural implications.…”