Anomalous Atmospheric Events Leading to the Summer 2010 Floods in Pakistan

Major rainstorms can occur in mountainous regions when air is lifted over the terrain. When the environment is especially unstable, storms may form that contain locally intense buoyant updrafts, heavy downpours of rain, and sometimes hail. The stratiform region features gentler rain but covers a much greater area and can last for long periods of time if the environment is favorable. The satellite radar on TRMM provides a unique vision of storms in regions inaccessible to land-based surface observations such as the mountains of Pakistan. The air in the depression is very humid, and the counter-clockwise winds on the northeast side of the depression bring a deep layer of moist air over land in the mountainous region to the northeast of the depression. This flow anomaly extended to lower levels, conveyed moisture into a region of Pakistan orthogonal to the Himalayan barrier, and was thus largely responsible for establishing the environment of the mesoscale rain systems that produced the flooding in the Indus region.