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Kharif
Drought (T Aman) in Bangladesh |
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Kharif Drought (T Aman) in Bangladesh |
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The
Kharif drought classification for delineating the drought prone areas
is based on the percentage of sub-humid and dry decades present in each
Kharif humid period. The dry sub-humid decades may be defined as a period
when precipitation (P) is less than half of the potential evapotranspiration
(PET), while the dry decade can be defined as a period when there is no
precipitation.The total number of dry days can be derived from the percentage
of decades in each Kharif humid period. Combinations of parameters for
each drought prone class were made with the frequency of these decades
on the basis of available soil moisture in the highland and medium highland.
The severity of either of the parameters was the dominant factor in ranking
in the higher classes of the drought prone areas.
Kharif drought prevails intermittently during June through
October on the highland and medium highland soils of the country. The
T. Aman crops grown on these lands are affected by drought. Four drought
prone classes have been identified in the Kharif period for the whole
country (Figure 1.2). Areas occupied by each drought prone class are
shown in percentage within brackets. These classes are Very severe (8.1
%), Severe (24.6 %), Moderate (30.7 %) and Slight (36.6 %).
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Impacts
of drought on crop yield: |
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The
T. Aman crop is also vulnerable to drought due to uncertain rain and its
uneven distribution. In the T. Aman season, drought has a great impact
on agricultural production. Early drought delays transplanting and harvesting
of this crop which affects the growing of Rabi crops after T. Aman. As
a result, a large area remains fallow after T. Aman is harvested. Early
drought also retards tillering and vegetative growth, which reduces the
yield of the crop. This crop also faces maximum drought stress during
its panicle initiation to the maturity stage. Yield reduction of T. Aman
in different Kharif drought prone classes is shown in the Table: |
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Intensity
of Kharif drought and yield reduction of T. Aman
crop |
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Drought
prone classes |
Yield
with no stress (t/ha) |
Reduction
over no stress yield (%) |
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Very
severe |
4.5
– 5.5 |
>
45 |
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Severe
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4.0
– 5.0 |
35
– 45 |
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Moderate
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4.5-
5.5 |
20
– 35 |
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Slight
|
3.5
– 5.0 |
<
20 |
| Source:
BARC, 1990 |
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Copyright ©
2005, Bangladesh Water Development Board |
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