68
3.4.2.3 Post-monsoon Rainfall Trend
The spatial distribution of the results of ITA, MK/mMK and Sen’s slope of rainfall
of post-monsoon are presented in Fig. 3.4c, g and k. In this period, most of the stations (66.73%) showed negative trends (ITA) in rainfall (Table 3.3), distributed
over whole study area except few pocket area (Fig. 3.4c) and approximately one
fifth (19.11%) of the stations showed significant negative trend (Z statistics) at the
confidence level of 99%, 95% and 90%, respectively, sparsely distributed over the
study area with maximum concentrated in the northern part (Table 3.4 and
Fig. 3.4k). Sen’s slope analysis revealed that average rainfall decreases at a rate of
0.08 mm/year over the area. The degree of decreasing trend for the major part of
the area varied between −0.01 and −6.50 mm/year (Fig. 3.4h). However, the highest decreasing trend (−6.50 mm/year) of rainfall obtained from ITA was observed
at Imphal in Manipur state of India. On the contrary, a little portion (7.15%) of the
observation station showed significant positive trend (MK/mMK) during
1951–2015 (Table 3.4) with the highest significant positive trend (4.28 mm/year)
for Teknaf in Bangladesh.
3.4.2.4 Winter Rainfall Trend
The rainfall trend in winter season obtained from ITA revealed that more than half
(70.75%) of the stations showed increasing trends, and rest of the stations (29.25%)
showed decreasing trend throughout the study area during 1951–2015 (Table 3.3
and Fig. 3.4d). On the contrary, results of the Z statistics denoted that about onesixth (16.28%) of the stations had a significant increasing tendency, and only 2.64%
stations showed significant decreasing tendency at different confidence levels
(Table 3.4 and Fig. 3.4l. The significant increasing trends were sparsely distributed
in the study area, and the magnitude of slopes was comparatively lower (0.01 to
1.82 mm/year) during this season with an average of 0.16 mm/year (Sen’s slope) for
the study area. The highest increasing (1.82 mm/year) trend was observed in India
at Doda stations under the state of Jammu and Kashmir. While spatiotemporal variation of rainfall of ITA test result is shown in Fig. 3.4d which clearly showed an
increasing trend in the whole study area except little portion of eastern, western and
southern part, more or less similar to the results of Z statistics (Fig. 3.4l). The highest increasing rate (3.06 mm/year) (ITA) was found also in Doda located in the state
of Jammu and Kashmir and the highest decreasing rate (−1.30 mm/year) was found
in India at Bagalkot station under the state of Karnataka. The significant increasing
trend of rainfall in this season is explained as the overactive of Western disturbance
and retreat monsoon.
T. Mandal et al.
3.4.2.3 Post-monsoon Rainfall Trend
The spatial distribution of the results of ITA, MK/mMK and Sen’s slope of rainfall
of post-monsoon are presented in Fig. 3.4c, g and k. In this period, most of the stations (66.73%) showed negative trends (ITA) in rainfall (Table 3.3), distributed
over whole study area except few pocket area (Fig. 3.4c) and approximately one
fifth (19.11%) of the stations showed significant negative trend (Z statistics) at the
confidence level of 99%, 95% and 90%, respectively, sparsely distributed over the
study area with maximum concentrated in the northern part (Table 3.4 and
Fig. 3.4k). Sen’s slope analysis revealed that average rainfall decreases at a rate of
0.08 mm/year over the area. The degree of decreasing trend for the major part of
the area varied between −0.01 and −6.50 mm/year (Fig. 3.4h). However, the highest decreasing trend (−6.50 mm/year) of rainfall obtained from ITA was observed
at Imphal in Manipur state of India. On the contrary, a little portion (7.15%) of the
observation station showed significant positive trend (MK/mMK) during
1951–2015 (Table 3.4) with the highest significant positive trend (4.28 mm/year)
for Teknaf in Bangladesh.
3.4.2.4 Winter Rainfall Trend
The rainfall trend in winter season obtained from ITA revealed that more than half
(70.75%) of the stations showed increasing trends, and rest of the stations (29.25%)
showed decreasing trend throughout the study area during 1951–2015 (Table 3.3
and Fig. 3.4d). On the contrary, results of the Z statistics denoted that about onesixth (16.28%) of the stations had a significant increasing tendency, and only 2.64%
stations showed significant decreasing tendency at different confidence levels
(Table 3.4 and Fig. 3.4l. The significant increasing trends were sparsely distributed
in the study area, and the magnitude of slopes was comparatively lower (0.01 to
1.82 mm/year) during this season with an average of 0.16 mm/year (Sen’s slope) for
the study area. The highest increasing (1.82 mm/year) trend was observed in India
at Doda stations under the state of Jammu and Kashmir. While spatiotemporal variation of rainfall of ITA test result is shown in Fig. 3.4d which clearly showed an
increasing trend in the whole study area except little portion of eastern, western and
southern part, more or less similar to the results of Z statistics (Fig. 3.4l). The highest increasing rate (3.06 mm/year) (ITA) was found also in Doda located in the state
of Jammu and Kashmir and the highest decreasing rate (−1.30 mm/year) was found
in India at Bagalkot station under the state of Karnataka. The significant increasing
trend of rainfall in this season is explained as the overactive of Western disturbance
and retreat monsoon.
T. Mandal et al.