Abstract:
This study used a series of mesoscale cloud-resolving simulations with Weather
Research and Forecasting (WRF) Model to reproduce the heavy rainfall and
persistent flooding event over Sri Lanka during 14th - 20th May 2016. This major
precipitation event, associated with a case of a depression over the Bay of Bengal in
the Indian Ocean, originated southeast of Sri Lanka and moved along the east coast
of Sri Lanka. This low-pressure system affected most of the country and caused
severe flooding and damages particularly in the western part of the Island during this
period. Timely availability of an accurate weather forecast can give the lead time for
hazards preparedness and minimize potential damages in such situations. Numerical
weather prediction with models like WRF is highly utilized for this purpose in many
parts of the world. Hence this study aims in finding the ability of the WRF model to
reproduce extreme heavy rainfall event and its usefulness in numerical weather
prediction in Sri Lanka. The model domain consists of one domain with 9 km grid
resolution. Model simulation fields are compared with available daily rainfall data
from in-situ weather stations of the Department of Meteorology, Sri Lanka. The
WRF model simulated the initiation of the low-pressure system and its development
along the east coast of Sri Lanka at nearly the right time. The corresponding
precipitation simulation was also reproduced in its spatial distribution aligning with
the weather station data, although the overall amount was overestimated. A
sensitivity experiment that excludes the orography over the model domain revealed
that orographic forcing over the central mountains in Sri Lanka is responsible for
about 23% increase in precipitation over the heavy rainfall area in the western Sri
Lanka during this event. Moreover, the WRF model able to capture the daily rainfall
tendency of this event over Sri Lanka, suggesting it has a potential for operational
use in numerical weather prediction in Sri Lanka.
