69
3.4.3 Annual Rainfall Trend
The trend analysis of annual rainfall using ITA, MK/mMK and Sen’s slope test and
their results are presented in Tables 3.3, 3.4 and Fig. 3.5. The ITA slope clearly
revealed that the decreasing (67.25%) trends are dominating throughout the study
area, mostly found in the eastern, central, western and south-eastern part except few
pocket regions. It is also observed from the results of MK/mMK that two-third
(65.50%) of 571 meteorological stations showed decreasing trends during the study
period, out of these, 121 station (32.35%), 46 stations (12.30%) and 32 stations
(8.56%) are statistically significant at 99 % , 95 % and 90%confidence level, respectively. The significant decreasing trends (Z statistics of MK/mMK) were mostly
concentrated in the central, western, extreme east and extreme southern part of the
study area and the magnitude of slope varied from −1.72 to −45.68 mm /year with
an average of −6.27 mm/year (Sen’s slope). On the other hand, 34.50% stations
showed an increasing trend (Z statistics) and of this 6.60%, 15.23% and 7.61% are
statistically significant at 99%, 95% and 90% confidence level, respectively.
Significant increasing trends are detected in the south-eastern part of India particularly in the coastal region of Bay of Bengal (Fig. 3.4c) and the trend varied from
2.26 mm/year to 27.86 mm/year (Sen
′
s Q = − 1.20 to 27.86). But while focused
individually, it was found that most of the stations in Bangladesh showed increasing
trends (60%) in annual rainfall, among them 33.33% were statistically significant
(α = 0.05). On the other hand, India was dominated by significant decreasing trend
(66.66%) for annual rainfall. Significant increasing trend of annual rainfall in
Bangladesh is explained as the location of the Mizo hills, Arakan Mountains, monsoon depression across the Bay of Bengal and early arrival of monsoon wind from
Bay of Bengal in relation to the western, northern and eastern parts of the country
(Ahmed and Kim 2003; Rahman et al. 2017).
Fig. 3.5 Distribution of slope and trend of annual rainfall (a) slope obtained from innovative trend
analysis (b) Sen’s slope, (c) Z statistics
3 Rainfall Insight in Bangladesh and India: Climate Change and Environmental…
3.4.3 Annual Rainfall Trend
The trend analysis of annual rainfall using ITA, MK/mMK and Sen’s slope test and
their results are presented in Tables 3.3, 3.4 and Fig. 3.5. The ITA slope clearly
revealed that the decreasing (67.25%) trends are dominating throughout the study
area, mostly found in the eastern, central, western and south-eastern part except few
pocket regions. It is also observed from the results of MK/mMK that two-third
(65.50%) of 571 meteorological stations showed decreasing trends during the study
period, out of these, 121 station (32.35%), 46 stations (12.30%) and 32 stations
(8.56%) are statistically significant at 99 % , 95 % and 90%confidence level, respectively. The significant decreasing trends (Z statistics of MK/mMK) were mostly
concentrated in the central, western, extreme east and extreme southern part of the
study area and the magnitude of slope varied from −1.72 to −45.68 mm /year with
an average of −6.27 mm/year (Sen’s slope). On the other hand, 34.50% stations
showed an increasing trend (Z statistics) and of this 6.60%, 15.23% and 7.61% are
statistically significant at 99%, 95% and 90% confidence level, respectively.
Significant increasing trends are detected in the south-eastern part of India particularly in the coastal region of Bay of Bengal (Fig. 3.4c) and the trend varied from
2.26 mm/year to 27.86 mm/year (Sen
′
s Q = − 1.20 to 27.86). But while focused
individually, it was found that most of the stations in Bangladesh showed increasing
trends (60%) in annual rainfall, among them 33.33% were statistically significant
(α = 0.05). On the other hand, India was dominated by significant decreasing trend
(66.66%) for annual rainfall. Significant increasing trend of annual rainfall in
Bangladesh is explained as the location of the Mizo hills, Arakan Mountains, monsoon depression across the Bay of Bengal and early arrival of monsoon wind from
Bay of Bengal in relation to the western, northern and eastern parts of the country
(Ahmed and Kim 2003; Rahman et al. 2017).
Fig. 3.5 Distribution of slope and trend of annual rainfall (a) slope obtained from innovative trend
analysis (b) Sen’s slope, (c) Z statistics
3 Rainfall Insight in Bangladesh and India: Climate Change and Environmental…