The role of upper-level dynamics and surface processes for the Pakistan flood of July 2010

Martius, Olivia; Sodemann, H.; Joos, H.; Pfahl, S.; Winschall, A.; Croci-Maspoli, M.; Graf, M.; Madonna, E.; Mueller, B.; Schemm, S.; Sedláček, J.; Sprenger, M.; Wernli, H. (2013). The role of upper-level dynamics and surface processes for the Pakistan flood of July 2010. Quarterly Journal of the Royal Meteorological Society, 139(676), pp. 1780-1797. Royal Meteorological Society 10.1002/qj.2082

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In July and August 2010 floods of unprecedented impact afflicted Pakistan. The floods resulted from a series of intense multi-day precipitation events in July and early August. At the same time a series of blocking anticyclones dominated the upper-level flow over western Russia and breaking waves i.e. equatorward extrusions of stratospheric high potential vorticity (PV) air formed along the downstream flank of the blocks. Previous studies suggested that these extratropical upper-level breaking waves were crucial for instigating the precipitation events in Pakistan. Here a detailed analysis is provided of the extratropical forcing of the precipitation. Piecewise PV inversion is used to quantify the extratropical upper-level forcing associated with the wave breaking and trajectories are calculated to study the pathways and source regions of the moisture that precipitated over Pakistan. Limited-area model simulations are carried out to complement the Lagrangian analysis. The precipitation events over Pakistan resulted from a combination of favourable boundary conditions with strong extratropical and monsoonal forcing factors. Above-normal sea-surface temperatures in the Indian Ocean led to an elevated lower-tropospheric moisture content. Surface monsoonal depressions ensured the transport of moist air from the ocean towards northeastern Pakistan. Along this pathway the air parcel humidity increased substantially (60–90% of precipitated moisture) via evapotranspiration from the land surface. Extratropical breaking waves influenced the surface wind field substantially by enhancing the wind component directed towards the mountains which reinforced the precipitation.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Institute of Geography > Physical Geography > Unit Impact
10 Strategic Research Centers > Oeschger Centre for Climate Change Research (OCCR)
08 Faculty of Science > Institute of Geography

UniBE Contributor:

Romppainen-Martius, Olivia

Subjects:

500 Science > 550 Earth sciences & geology
900 History > 910 Geography & travel

ISSN:

0035-9009

Publisher:

Royal Meteorological Society

Language:

English

Submitter:

Monika Wälti-Stampfli

Date Deposited:

16 Jan 2014 10:05

Last Modified:

14 Nov 2016 08:24

Publisher DOI:

10.1002/qj.2082

Uncontrolled Keywords:

heavy precipitation, Pakistan, moisture sources, evapotranspiration, potential vorticity, inversion

BORIS DOI:

10.7892/boris.39475

URI:

https://boris.unibe.ch/id/eprint/39475

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