Unraveling the Origin of Moisture for South West Indian Monsoon Precipitation Events over Periyar River Basin using Lagrangian Approach

Abstract:

In recent decades, as the magnitude and frequency of extreme events have been increasing, identifying moisture sources and pathways for extreme events acquired prominent importance. This will help in modelling, simulating, and forecasting extremes in space and time and, consequently, for effective resources management. A Lagrangian diagnostic approach is used to discover the direct evaporative moisture sources as well as sources of moisture change due to other physical processes for precipitation events higher than various percentiles (75^th, 80^th, 85^th, 90^th, 95^th and 99^th percentiles) during summer monsoon of 1980-2018 over Periyar basin. The HYSPLIT model, along with ECMWF Interim reanalysis dataset, was deployed to track the air parcels and to study their properties. The moisture originated from land and ocean of events higher than various percentiles range from 3.17% to 6.24% and 96.83% to 93.76% respectively, of the total moisture below the Boundary Layer (BL). The major moisture source regions and their percentage contribution to moisture precipitated over the target area (i.e., Periyar basin) are also determined. For all percentiles, time taken by the air parcels from different latitudes below the BL range from 5 to 8.9 days, and the same above the BL range from 5 to 9.75 days to reach the target area. As the number of events increases variability among the events captured by the Lagrangian approach improves. However, this approach is more appropriate for heavy rainfall events. The major moisture contributor for JJAS maximum precipitation event of the Periyar basin, which is also the cause of the 2018 Kerala flood, is the Indian Ocean.