Nissan, H.
Aalst, M.
Burkart, K.
Mason, S.
Perez, E.


American Meteorological Society

Year of Publication:


This paper proposes a heat wave definition for Bangladesh that could be used to trigger preparedness measures in a heat early warning system (HEWS) and explores the climate mechanisms associated with heat waves. A HEWS requires a definition of heat waves that is both related to human health outcomes and forecastable. No such definition has been developed for Bangladesh. Using a generalized additive regression model, a heat wave definition is proposed that requires elevated minimum and maximum daily temperatures over the 95th percentile for three consecutive days, confirming the importance of night-time conditions for health impacts. By this definition, death rates increase by about 20% during heat waves; this result can be used as an argument for public health interventions to prevent heat-related deaths. Furthermore, predictability of these heat waves exists from weather to seasonal timescales, offering opportunities for a range of preparedness measures. Heat waves are associated with an absence of normal pre-monsoonal rainfall brought about by anomalously strong low-level westerly winds and weak southerlies, detectable up to approximately ten days in advance. This circulation pattern occurs over a background of drier-than-normal conditions, with below-average soil moisture and precipitation throughout the heat wave season from April to June. Low soil moisture increases the odds of heat wave occurrence for 10 to 30 days, indicating that sub-seasonal forecasts of heat wave risk may be possible by monitoring soil moisture conditions.

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