Ram Mohan, H S; Subash, N; Sikka, A K(Springer, 2010)
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Abstract:
Mann–Kendall non-parametric test was employed for observational trend detection of monthly, seasonal and
annual precipitation of five meteorological subdivisions of
Central Northeast India (CNE India) for different 30-year
normal periods (NP) viz. 1889–1918 (NP1), 1919–1948
(NP2), 1949–1978 (NP3) and 1979–2008 (NP4). The trends
of maximum and minimum temperatures were also investigated.
The slopes of the trend lines were determined using the
method of least square linear fitting. An application of Morelet
wavelet analysis was done with monthly rainfall during June–
September, total rainfall during monsoon season and annual
rainfall to know the periodicity and to test the significance of
periodicity using the power spectrum method. The inferences
figure out from the analyses will be helpful to the policy
managers, planners and agricultural scientists to work out
irrigation and water management options under various
possible climatic eventualities for the region. The long-term
(1889–2008) mean annual rainfall of CNE India is
1,195.1 mm with a standard deviation of 134.1 mm and coefficient of variation of 11%. There is a significant decreasing
trend of 4.6 mm/year for Jharkhand and 3.2 mm/day for CNE
India. Since rice crop is the important kharif crop (May–
October) in this region, the decreasing trend of rainfall during
themonth of July may delay/affect the transplanting/vegetative
phase of the crop, and assured irrigation is very much needed
to tackle the drought situation. During themonth of December,
all the meteorological subdivisions except Jharkhand show a
significant decreasing trend of rainfall during recent normal
period NP4. The decrease of rainfall during December may
hamper sowing of wheat, which is the important rabi crop
(November–March) in most parts of this region. Maximum
temperature shows significant rising trend of 0.008°C/year (at
0.01 level) during monsoon season and 0.014°C/year (at 0.01
level) during post-monsoon season during the period 1914–
2003. The annual maximum temperature also shows significant
increasing trend of 0.008°C/year (at 0.01 level) during
the same period. Minimum temperature shows significant
rising trend of 0.012°C/year (at 0.01 level) during postmonsoon
season and significant falling trend of 0.002°C/year
(at 0.05 level) during monsoon season. A significant 4–
8 years peak periodicity band has been noticed during
September over Western UP, and 30–34 years periodicity
has been observed during July over Bihar subdivision.
However, as far as CNE India is concerned, no significant
periodicity has been noticed in any of the time series.