BSc-MSc (Integrated)

The Western Ghats with its strategic position plays a great role in
channelling the summer monsoon rain into the mainland. The natural ecosystems
and human livelihoods of this region are highly dependent on the Indian Summer
Monsoon rainfall and even the slightest change can trigger a change in these
systems. The global climate changing scenario is having its toll in the monsoonal
system over this region. The extreme events in the region have been analysed for
trends using Mann Kendall method and the return periods of the one day maximum
rainfall has been modelled using Generalized Extreme Value (GEV) theory.
The mean annual monsoonal rainfall over the region is 1616.15 mm and the
standard deviation is 242.966.It was observed that the mean annual monsoonal
rainfall varied from 231.4mm in grid 117 to 3416 mm in grid 253. The one day
maximum rainfall extracted from the 32 constituent grids for the entire period
showed a variation from 118.63 mm in 1981 to 316.63 mm in 2005. The temporal
variation in one day maximum rainfall for the time series had a significant trend.
The values were seen to increase steadily and a profound increase was observed in
the recent decades. When the One day maximum rainfall was analysed for different
latitudes, two latitudes (14°N and 21°N) had significant positive trends in One Day
Maximum Rainfall in the whole region. Out of the 32 grids, 7 grids (186, 359, 394,
428, 429, 497 and 498) showed a significant rising trend in one day maximum
rainfall. It was also observed that during the recent years, the occurrence of One
day maximum Rainfall has shifted to the far end of the season.
The number of grids getting heavy, very heavy and extreme rainfall events
was found to have increased during the later years of the study. No significant trend
in the instances of occurrence of heavy rainfall over the years was observed. But a
significant trend was observed in the occurrences of rainfall events of very heavy
and extreme magnitudes. When Split period analysis of the contribution of
moderate and high intensity rainfalls was carried out, it was observed that the share
of high intensity rainfalls had increased and a decrease was observed in the share
of moderate events over the years. The return period analysis of the one day
maximum rainfall events was done and it was observed that the 2 year, 5 year, 10
year, 25 year, 50 year and 100 year return levels of rainfall as 186.2mm, 224.3 mm,
250.2 mm, 283.8 mm, 309.3 mm and 335.1 mm for the complete region. The return
levels for the two year return period were seen to be over 100 mm for the grids of
184 (118mm), 219 (114.9mm), 253 (145.8mm), 285 (104.5mm), 357 (147.6 mm),
392 (144.2mm), 427 (129.9mm) and 462 (122.4mm).
A significant rising trend in the extreme events of summer monsoon rainfall
over the Western Ghats was observed. This calls for better planning in all areas of
livelihoods and management strategies to contain the disasters of a changing
climate.