DecadeS

89INDIA

4.4 Post-monsoon .1 Average rainfall

4.4.2 Rainfall anomaly

4.4.2.5 DecadeS

rainfall anomaly is -0.5 mm/day through Srimongal and increases through zero to positive towards northeast direction. In the southeast hilly regions of the country rainfall anomaly line is anomalous.

27

INDIA

BAY OF BENGAL

ati

INDIA Post-monsoon rainfall anomaly (Decade4)

( 1980-1989)

oBogra /

( OMymensing

o;..

DJessore OIshurdi o;...

INDIA 25

23

21 26

22

88 89 90 91

Longitude (E)

92 93

Fig. 4.4.2.4. Rainfall anomaly (mm/day) during post-monsoon over Bangladesh for Decade4.

63

27

BAY OF BENGAL INDIA

Post-monsoon rainfall anomaly (DecadeS) (1990-1999)

oDSatkhiraDKhulna .2

ORajshahi OIshurdi

INDIA 26

21 23 25

22

88 89 90 91

Longitude (E)

92 93

Fig. 4.4.2.5. Rainfall anomaly (mm/day) during post-monsoon over Bangladesh for DecadeS.

64

27

BAY OF BENGAL

Rainfall anomaly over Bangladesh (Pre-monsoon) (1950-1999)

INDIA 26

21 22

INDIA

25

)

D~shahi

I

""' _{DIsh rdi}

b

₀ ²⁴

-

^,

'" _.a

.-

_ti:i

...:l 23

88 89 90 91

Longitude (E)

92 ₉₃

-

Fig. 4.5.1. Rainfall anomaly (mmJday) during pre-monsoon over Bangladesh.

65

northeastern region of the country. In the southeast hilly region of the country rainfall anomaly increases from south to northward direction.

Rainfall anomaly over Bangladesh during monsoon is shown in Fig. 4.5.2. A- 4 mm/day rainfall anomaly line passes through Bogra, Tangail, Faridpur, Khulna and Satkhira. A -2 nun/day rainfall anomaly line passes through Srimongal and Mymensing and extends up to the northern most comer of the country. From this line rainfall anomaly increases through zero to positive values towards north- northeast direction. Another -2 mm/day rainfall anomaly line passes through Comilla, Chandpur, Barisal and extends up to the southwest comer of the country. From this line rainfall anomaly also increases through zero to positive values towards southeast direction in the southern part of the country. In the southeast region of the country rainfall anomaly increases from negative value to positive values from east to west (negative anomaly means decrease in rainfall and positive anomaly means excess of rainfall).

Rainfall anomaly (nun/day) over Bangladesh during post-monsoon is shown In Fig. 4.5.3. From the central part of the country rainfall anomaly increases negatively (i.e. rainfall decreases) towards west. In the southern coastal region of the country rainfall anomaly increases positively (i.e. rainfall increases) towards south. In the northeast region of the country rainfall anomaly increases positively towards north-northeast direction. In the southeast hilly region of the country both positive and negative anomaly are seen. Rainfall anomaly ranges from -1.5 to 1.5 mm/day over the country during this season.

At last distribution of average rainfall from March to November for each decade and also during 1950-1999 have been studied and is presented in the following pages.

Daily average has been made for each station from March to November daily rainfall data during 1950-1999. The distribution of this average rainfall (nun/day) is shown in Fig. 4.6.0. Rainfall slowly increases from west to eastward in the western part of the country and rapidly increases towards northeast direction in the

.

.

northeastern part of the country. In the southern part of the country average rainfall .•

27

BAY OF BENGAL

INDIA

ensing

INDIA

ODhak.

Faridpur OBogr.

OJessore

Rainfall anomaly over Bangladesh (Monsoon) (1950-1999)

OIshurdi

INDIA

21 23 26

22 25

88 89

90 91

Longitude (E)

92 93

Fig. 4.5.2. Rainfall anomaly (mm/day) during monsoon over Bangladesh.

67

27

BAY OF BENGAL

26

2

23

INDIA

22

21

Rainfall anomaly over Bangladesh (Post-monsoon) (1950-1999)

INDIA

INDIA

88 89 90 91

Longitude (E)

92 93

Fig. 4.5.3. Rainfall anomaly (mm/day) during post-monsoon over Bangladesh.

68

Average rainfall all over the country is 7.38 mrn!day 27

2

DR.jsh.hi

~

DIshur i

..,

24

]

'.0

j

23

INDIA

22

21

INDIA

•

BAY OF BENGAL

INDIA

ati

88 89 90 91

Longitude (E)

92 93

Fig. 4.6.0. Distribution of average rainfall (mm/day) from March to November during 1950-1999.

69

Increases towards southeast direction. In the southeast region average rainfall increases from east to westward. It is worth mentioning that the average rainfall over all 30 stations during this period is 7.38 mm/day.

Distribution of average rainfall (mm/day) over Bangladesh from March to November for Decadel is shown in Fig. 4.6.1. Average rainfall increases from west to eastward in the western part of the country. Rainfall increases rapidly towards north- northeast direction in the northeast part of the country. Rainfall also increases towards coastal region. In the southeast part of the country rainfall increases from east to westward direction.

Distribution of average rainfall (mm/day) over Bangladesh from March to November for Decade2 is shown in Fig. 4.6.2. There is a closed contour encircling Ishurdi with average rainfall 4 mm/day. A 6 mm/day average rainfall line passes through Mymensing, Srimongal, Dhaka and extends up to southeast part of the country. From this line average rainfall increases towards northeast direction in the northeast part of the country. Rainfall also increases towards southeast direction in the coastal region. In the southeast hilly region of the country rainfall increases from north to southward direction.

Distribution of average rainfall (mm/day) over Bangladesh from March to November for Decade3 is shown in Fig. 4.6.3. There is a closed contour encircling Faridpur, Dhaka and Tangail marked as 6 mm/day. Another 6 mm/day-average rainfall linc" passes through Rangpur, Mymensing, Comilla and extends up to• southwest region of the country. From this line rainfall increases towards northeast direction in the northeast region of the country. Rainfall also increases towards coastal region. In the southeast region of the country distribution of average rainfall is anomalous.

Distribution of average rainfall (mm/day) over Bangladesh from March to November for Decade4 is shown in Fig. 4.6.4. In many places over the country rainfall is only 6 mm/day. Average rainfall increases from west to eastward in the western part of the country and then increases towards northeast direction in the north

27

BAY OF BENGAL

26

25

,-..

_{Olshur i}

b .,

²⁴

"t:l

.~.E!

...:Itil

••• OJes ore

23

os

INDIA

22

21

Average Rainfall

March-November (Decade 1)

INDIA

88 89 _{90 91}

Longitude (E)

92 93

Fig. 4.6.1. Distribution of average rainfall (mm/day) from March to November during 1950-1959.

71

27

26

2

~ 24

~

.a

.~c;l ...:I

23

INDIA

22

21

88 89

Average Rainfall

March-November (Decade2)

INDIA

BAY OF BENGAL

90. 91

Longitude (E)

92 93

Fig. 4.6.2. Distribution of average rainfall (mm/day) from March to November during 1960-1969.

72

27

BAY OF BENGAL