Abstract:
This study investigates long-term variation of low-level vertically integrated moisture
flux (VIMF) for 37-year from 1979 to2015 and its contributions to the total rainfall over
South Asia (SA), which includes also the Bay of Bengal and the eastern part of Arabian
Sea. For this purpose wind, specific humidity, precipitation and evaporation data are
collected from ERA-Interim reanalysis data generated by European Centre for Medium-
Range Weather Forecasts (ECMWF) having horizontal resolution of approximately 80
km. The region is further sub divided into six areas i.e. South-West (SW), Bay of Bengal
(BoB), South-East (SE), North-West (NW), Bangladesh and surrounding (BAN) and
North-East (NE) for understanding details of spatial and temporal characteristics of lowlevel
moisture flux and its effect on precipitation. SW, BoB and SE domains are
considered as Southern part and NW, BAN and NE domains are considered as Northern
part. The averaged VIMF is found to be 113.71 kg m-1 s-1 for the total study area. The
annual variation of VIMF remains almost constant for 37 years over SA with average
increasing rate of only 0.14% per year. Southern parts of the study area (SW, BoB and
SE) acquire 67% of the total flux, whereas, 33% of the total moisture flux is observed
over the Northern parts (NW, BAN and NE), which are mainly the land area. According
to season, about 41% of the total VIMF is found to be advected in the monsoon season,
whereas, only 17% of the total VIMF is found in the winter season. The monthly value of
VIMF (191.74 kg m-1 s-1) is highest in July over SA which is 33% more than the
minimum value in March. For six individual domains, highest amount of VIMF (27% of
the total VIMF) is found over the BoB whereas only 6% of the total VIMF is found over
the NE domain. The SW, SE, NW and BAN regions receive 21%, 19%, 13% and 14% of
the total flux, respectively. Annual variation of VIMF for individual domain is also found
constant except in the NE domain where VIMF is increased significantly with coefficient
of determinant (R²) value of 0.54. However, the NE region has the lowest amount of
VIMF (35.01 kg m-1 s-1). Seasonal variation in the domains indicates that the Southern
parts of the study area have two times higher VIMF than the Northern parts during the
the monsoon season. The lowest amount of VIMF approximately 29.73 kg m-1 s-1 is
observed in January for the Northern region and for the Southern region the lowest value
of approximately 76.78 kg m-1 s-1 is found in March.
