Severe Flooding in Pakistan in August 2022 Associated with an Unusually Amplified Large-Scale Flow Pattern that Facilitated Midlatitude-Tropical Interactions

Widespread heavy rains cause catastrophic flooding over parts of Pakistan and India in August 2022. The extensive flooding killed more than 1500 people and caused billions of dollars in damages and economic losses. This aforementioned extensive flooding was associated with anomalously heavy monsoon rains, westward-moving Bay of Bengal cyclones, and rapidly melting glaciers. An important antecedent to the severe flooding that occurred across Pakistan and India was widespread severe weather outbreak that occurred across southern Europe in mid-August 2022 in conjunction with a rare serial derecho. This derecho was associated with an unusually strong summer 500-hPa cutoff cyclone that deepened as it moved southeastward across France into the western Mediterranean Sea and northern Italy. This cutoff cyclone subsequently turned northeastward and weakened as it moved toward central Europe on the western side of a strong blocking anticyclone situated over higher-latitude eastern Europe and western Russia. This blocking anticyclone served as a “meteorological traffic cop” for a series of eastward-propagating upper-level cyclonic disturbances of western European origin that subsequently reached central and eastern Asia.

On the eastern side of the aforementioned blocking anticyclone a parade of troughs that had crested this anticyclone dropped south-southeastward toward a persistent trough that was situated across eastern Iran, Afghanistan, Pakistan, and the Tibetan Plateau. A persistent quasi-stationary 700-hPa cutoff cyclone associated with this trough was located on the border of Pakistan and India. This cutoff cyclone facilitated the northeastward transport of very moist air (precipitable water values > 60 mm and integrated water vapor transport values > 1000 kg/m/s) across the Arabian Sea toward western India and from there northwestward toward Pakistan. Preliminary evidence suggests that the aforementioned moist southwesterly flow across the Arabian Sea was enhanced by a merger with a westward-directed equatorial flow of very moist air from the tropical western Pacific Ocean. Preliminary evidence also suggests that the extraordinary heavy rains that fell across Pakistan were associated more with duration than with rainfall intensity, given the large-scale “flow constipation” that persisted from eastern Europe to western Asia during much of August 2022. The key player in the aforementioned “flow constipation” process was an unusually persistent, high-amplitude, quasi-stationary ridge centered over eastern Europe and western Russia.