Construction and Quality of Best Tracks Parameters for Study of Climate Change Impact on Tropical Cyclones over the North Indian Ocean during Satellite Era - Monitoring and Prediction of Tropical Cyclones in the Indian Ocean and Climate Change - page 12

Table 5: Trends (per decade) in frequency of (i) CDs, (ii) CS or higher intensity
and (iii) SCS or higher intensity over BOB, AS and NIO as a whole for the period of
1965-2010

Period Cyclonic Cyclonic storms Severe cyclonic

disturbances or higher or higher

intensity intensity

R 2 R 2 R 2 Trend Trend Trend

Bay of Bengal (BOB) -1.5 0.51 -0.64 0.36 -0.52 0.33

Arabian Sea (AS) -0.1 0.01 -0.02 0.001 0.00 0.00

North Indian Ocean (NIO) -1.6 0.44 -0.66 0.32 0.52 0.22

4.4 Trend in Frequency of Very Severe Cyclonic Storm

(VSCS) or Higher Intensity Storms

There is significant (at 95% level of confidence) decreasing trend over the
BOB and NIO as a whole (Fig. 3). The frequency has decreased at the rate of
about 0.56 per decade over the NIO. Further analysis indicates that the trend is
significant during monsoon (June-September) and post-monsoon (October-
December) seasons (Table 6). Mandal and Prem Krishna (2009) have also
shown decreasing trend of frequency of very severe TCs over the NIO during
1965-2008 (satellite era) and no trend in the maximum wind associated with
very severe TCs during the same period.

Table 6: Trends (per decade) in frequency of VSCS during pre-monsoon, monsoon
and post-monsoon seasons and year as a whole for the period of 1965-2010

R 2

Period Trend (Per decade)

Pre-monsoon season -0.04 0.01

Monsoon season -0.18 0.14

Post-monsoon season -0.35 0.21

Year as a whole -0.56 0.28

5. Conclusions

The annual frequencies of CDs, CS or higher intensity, SCS or higher intensity
and VSCS or higher intensity storms show significant decreasing trend over
the BOB and NIO as a whole during the satellite era (1961-2010). However,
there is no significant trend over the AS during the same period.
The NIO being the data sparse region, the best track estimates are subject
to errors of about 55 km in the mid-oceanic region during satellite era. There is
scope for improvement, as evident from the recent past cases, due to existing
and proposed buoy network over the NIO, ongoing modernization programme
of IMD resulting in improved observational system like Doppler weather radar