Analysis of Two Heavy Rainfall Episodes in May 2022 and June 2022 in Southern Parts of Assam, Northeast India
摘要
Two heavy rainfall episodes occurred during 12–16 May 2022 and 14–18 June 2022 over the southern districts of Assam, namely Dima Hasao, Cachar, Hailakandi, and Karimganj in the northeast region of India (NER). These episodes resulted in two consecutive catastrophic flood events, causing large-scale infrastructure damage and enormous losses of property and human life. Analysis of vertically integrated moisture flux convergence (VIMFC), Vorticity-Budget, vertical motion, and Iso-surface of wind have been carried out to look into the driving mechanism of two heavy rainfall episodes. A sharp rise (> 1 × 10–5 kg m−2 s−1) in district-averaged VIMFC at 1000–700 hPa levels was observed between 2100 UTC on 13 May and 0600 UTC on 14 May, with a peak value of 3.05 × 10–5 kg m−2 s−1 at 0000 UTC on 14 May over Dima Hasao district during the first episode. During the second episode, an increase in district-averaged VIMFC at 1000–700 hPa levels was noted from 0000 to 0600 UTC on 18 June, peaking at 6.88 × 10–5 kg m−2 s−1 at 0600 UTC over Cachar district. These observations indicate that the high VIMFC over the study area was primarily due to the convergence of lower-level southwesterlies from the Bay of Bengal. Common factors for both episodes include strong moisture transport from the Bay of Bengal via southwesterly winds, resulting in increased VIMFC at lower levels. Furthermore, vertical velocity was positive and more pronounced during these episodes. Vorticity budget analysis shows that during both the episodes, the horizontal advection term and convergence term contributed positively at lower levels, while the vertical advection term contributed positively between low and mid-levels. This suggests that the transport of low-level vorticity to upper and middle levels fueled deep convection, which contributed to the heavy rainfall and subsequent flooding.