Monsoon Low Pressure Systems and Hydrometeorological Disasters
UC Berkeley researchers geolocated each event in a large dataset of human mass-casualty disasters and associated it with elements of a multi-decadal storm track dataset. The researchers found that a particular type of storm called a monsoon low-pressure system produces more than half of hydrometeorological disasters in South Asia during summer.
Transient atmospheric vortices called monsoon low-pressure systems are known to produce extreme precipitation, but their quantitative contribution to human mass-casualty events was unknown. This study showed that the most intense low-pressure systems, called monsoon depressions, produce the largest number of disasters and are predictable several days in advance.
Transient atmospheric vortices called monsoon low-pressure systems (LPS) generate a large fraction of total rainfall over South Asia and often produce extreme precipitation. Here, we assess the influence of these storms on the occurrence of disasters, using information from the Emergency Events Database (EM-DAT) that we geocoded and then associated with LPS tracks. We show that more than half of hydro-meteorological disasters over South Asia during summer are associated with these LPS events. Weaker LPS (which are called monsoon lows) occur more frequently than stronger LPS (called monsoon depressions), but the stronger LPS produce a larger number of disasters. Furthermore, although many prior studies have shown that the peak rainfall in LPS falls southwest of the vortex center, the disasters are concentrated on the northern edge of the LPS tracks, along the Himalayas and upper basins of the Ganga and Brahmaputra rivers. Observations show a sharp peak in rainfall on the day of disasters, confirming the physical link between LPS and these hydro-meteorological disasters. A similar peak in rainfall is found in weather forecasts made up to five days before the disaster, suggesting that short-term precipitation forecasts can be useful in disaster preparation.