Agriculture Reference
In-Depth Information
rainfall exhibited significant increasing trends, while contribution of July
rainfall exhibited decreasing trend. However, no significant trends in the
number of breaks and active days during the south-west monsoon season
during the period 1951-2003 were observed.
2.2.4 CLOUD COVER OVER THE INDIAN SEAS
Both total and low cloud cover over Arabian Sea and the equatorial Indian
Ocean are observed to decrease during the ENSO events. However, cloud
cover over Bay of Bengal is not modulated by the ENSO events. On in-
terdecadal scale, low cloud cover shifted from a “low regime” to a “high
regime” after 1980, which may be associated with the corresponding in-
terdecadal changes of sea surface temperatures over north Indian Ocean
observed during the late 1970s (Rajeevan et al.
,
2000).
2.2.5 HEAT WAVE AND COLD WAVE
A significant increase was noticed in the frequency, persistency and spatial
coverage of both of these high frequency temperature extreme events (heat
and cold wave) during the decade (1991-2000) (Pai et al., 2004).
2.2.5.1 CYCLONES
1. A slight decreasing trend in the annual frequency of cyclones that
formed over Bay of Bengal (BOB) during 1900-2009 is seen. But,
there is a slight increasing trend in the annual frequency of severe
cyclones that formed over the BOB during the same period. Also,
there is an increasing trend in the intensification of cyclones to
severe cyclones.
2. No trend is noticeable in the frequencies of cyclones and severe
cyclones that formed over the Arabian Sea during the period 1900-
2009.
3. Decreasing trend in frequency of cyclonic disturbances (depres-
sion and above) during 1891-2009 and increase in low-pressure
areas during 1888-2009 have been observed.
