Catastrophic Heavy Rainfall Episode over Uttarakhand during 16-18 June 2013 - Observational Aspects

Widespread very heavy to extremely heavy rainfall occurred over Uttarakhand and its neighbouring states during 16-18 June 2013, which caused flash floods, landslides, large-scale loss of lives and damage to property. The present study analyses the dynamical and thermodynamical features associated with this torrential rainfall episode. The analysis suggests that due to strong interaction between an oncoming midtropospheric trough in the westerlies and the strong lower-tropospheric southeasterly monsoon wind flow in association with a monsoon low-pressure system over the North Indian region, a lower tropospheric wind convergence zone developed over Uttarakhand and its neighbouring regions. A strong Bay of Bengal current of air with wind speed of 40 kts in the northern periphery of the monsoon low, pumped a lot of moisture into the region. Supported by strong orographic effect due to high terrain and strong moisture feeding from both the Arabian Sea and the Bay of Bengal, a large-scale quasistationary regenerative mesoscale convective system (MCS) developed over the zone of convergence. The episode was comparable to the 2010 Leh flash flood episode, in that the synoptic conditions were similar in both cases. However, while the Leh episode resulted from repeated surges of westward travelling MCS across the Tibetan Plateau, the present case was due to quasistationary regenerative MCS over the region.