Wednesday, 25 January 2012: 9:15 AM
Changes in Monsoon Extremes Affecting Climate Prediction—Example of the 2010 Pakistan Floods
Room 354 (New Orleans Convention Center )
Meteorological conditions related to the 2010 Pakistan floods were examined in the context of monsoon dynamics and climate change. Case and climatological analyses suggest that summer precipitation in northern Pakistan comprises two distinct phases: a) a pre-monsoon trough phase (July) whose rainfall is more episodic and intense, occurring prior to arrival of the monsoon trough; and b) a monsoon trough phase (August) whose rainfall is persistent, yet less episodic, driven by northward migration of the monsoon trough. Analyses of conditional instability, moisture flux, and circulation features support a persistent increase in conditional instability during the July pre-monsoon trough phase, accompanied by increased frequency of heavy rainfall events. Conversely, evidence does not support intensification of the August monsoon trough phase. The increased convective activity during the pre-monsoon trough phase agrees with the projected increase in the intensity of heavy rainfall events over northern Pakistan. Large-scale circulation analysis reveals an upper-level cyclonic anomaly over and to the west of Pakistan – a feature empirically associated with weak monsoon and therefore would give false prediction for the strong monsoon in 2010. The analysis also suggests that the anomalous circulation in 2010 is not sporadic but rather is part of a long term trend that defies the typical linkage of strong monsoons with an anomalous anticyclone in the upper troposphere. This long term trend of the upper tropospheric circulation may be linked to increased extremeness of precipitation events in other midlatitude regions.
Supplementary URL: http://www.agu.org/pubs/crossref/2011/2011JD015760.shtml