Pakistan's two-stage monsoon and links with the recent climate change

Abstract

[1] Meteorological conditions related to the Pakistan floods of 2010 were examined in the context of monsoon dynamics and large-scale circulations. Case and climatological analyses suggest that summer precipitation in northern Pakistan comprises two distinct phases: (1) a premonsoon trough phase (July) whose rainfall is more episodic and intense, occurring prior to arrival of the monsoon trough, and (2) 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 premonsoon 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 premonsoon trough phase agrees with the projected increase in the intensity of heavy rainfall events over northern Pakistan. Largescale circulation analysis reveals an upper-level cyclonic anomaly over and to the west of Pakistan-a feature empirically associated with weak monsoon. 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.

Impact of Climate Change on Flood Frequency and Intensity in the Kabul River Basin

“…Increases in extreme precipitation events and a rise in temperature are the major sources of floods in the HKH region e.g., [1,67,68]. In our study, FFA has been carried out for the near future and far future peak flows (see Figure 7).…”

Tropical SST forcing on the anomalous WNP subtropical high during July–August 2010 and the record-high SST in the tropical Atlantic

“…10a, b, 11a, b), where a strong Indian summer monsoon and record-breaking flood occurred from late July to mid-August 2010 (e.g., Wang et al 2011;Webster et al 2011). Furthermore, a broad anticyclonic circulation over the Eurasian continent was observed, but the simulated stream function was nearly normal.…”

Brief Communication: Climatic, meteorological and topographical causes of the 16–17 June 2013 Kedarnath (India) natural disaster event

“…The intrusion of cold air in the presence of moist/humid air along with orographic uplift could have triggered intense convection and low convergence, resulting in heavy rainfall over the Uttrakhand state. In a similar case of extreme rainfall (July-early August, 2010), associated with devastating floods in Pakistan (Hong et al, 2011;Wang et al, 2011;Lau and Kim, 2012), Hong et al (2011) advocated that southward penetration of cold dry air, associated with the trough east of the blocking of air masses, induced anomalous low-level convergence and upward motion and provided a favorable environment for the northward propagation of monsoon surges. Houze et al (2011) attributed this event to an association with the anomalous propagation of a depression formed over the Bay of Bengal.…”