The 2010 and 2014 floods in India and Pakistan: dynamical influences on vertical motion and precipitation

Abstract: Devastating floods in northeast Pakistan and northern India occurred in July 2010 and September 2014 as a consequence of extreme precipitation events. The 2010 and 2014 flood events had similar synoptic flow patterns that led to an anomalously high moisture content in the flood region. The quasi-geostrophic omega equation is inverted in order to attribute components of the large-scale vertical motion profile to synoptic forcing, diabatic heating, and mechanically forced orographic ascent. The results show that diabatic heating is the dominant contributor to the large-scale vertical motion, and suggest that the orographic forcing by flow over the Himalayas is the dominant mechanism by which the convection that produces the heating is forced. Analysis of a longer data record shows that instances of extreme precipitation in this region over the last eleven years are closely associated with simultaneously large values of orographic forcing and column-total precipitable water vapor.