[A-CG45] AsiaPEX field campaign strategies for changing Asian monsoon precipitation

[ACG45-01] Long term changes in the Frequency of Local Severe Convective Storm (LSCS) days in Assam

*Rahul Mahanta¹, Prolay Saha¹, Yusuke Yamane², Toru Terao³, Hideyuki Kamimera⁴ (1.Cotton Univ., 2.Tokoha Univ., 3.Kagawa Univ., 4.NIED)

Keywords:LSCS, Assam, CAPE, Temperature, Specific-humidity, Global warming

Local Severe Convective Storms (LSCS) are major hazardous meteorological phenomena in Assam, an Indian State and accurately predicting their trends is fundamental to the economic development of the state. This research investigated LSCS variability across all the districts in Assam, over a 55-year study period (1962–2016). A brief statistical analysis was applied for the assessment of variability. For detecting trends in monthly, seasonal, and annual scales both Nonparametric Mann-Kendall (MK) statistical tests with Sen's slope estimator and least square technique were employed. The confidence levels of slopes of trends are determined by Student’s t-test. The results underscore a blend of both positive and negative trends in monthly, seasonal, and annual LSCS days. The inter-annual LSCS days exhibit an increasing trend of ∼1 day per decade in Assam. The trend is displayed mainly in the increasing LSCS days in pre-monsoon, monsoon, and post-monsoon seasons except in winter, when the variation is negative and significant in major parts of Assam. The trend was also compared for two periods 1962-1989 and 1990-2016 to isolate meteorological factors causing the observed trend. Further, the variation in LSCS day frequency closely follows the variation in atmospheric instability, specific humidity, and temperature over Assam. We expect the changes occurring in the interaction between regional topography with different climate forcing, and other meteorological conditions arising due to human activity to be responsible for the existence of a trend in LSCS days. This study shows that in Assam we have comprehensively accumulated storm reports of evidence that the LSCS events have already changed in very significant ways. The findings from this study agree with IPCC observations that expect a significant increase in severe storm-induced extremes in a warming world, due to the increased amount of water vapor in the atmosphere, one of the primary ingredients in the development of LSCS.