Rabi Drought

The drought problem in Bangladesh perhaps reaches it peak during the Rabi season that extends from mid-October to early April. December, January, and February are the months with negligible rainfall across the 1.75 million ha of the combined catchment area of the Ganges-Brahmaputra-Meghna (GBM) river systems in the eastern Himalayan region (Ahmad et al., 1994). As a result, river flows are at their minimum. From March to early April, the temperatures shoot up rapidly, particularly during the day. These conditions lead to high potential evapotranspiration (PET), causing acute moisture stress in the topsoils. When residual moisture can no longer support the standing crops, drought develops and adversely affects crop production. The land with very poor moisture-holding capacity, found in the Barind tract, faces the worst consequences of drought during the Rabi season.

Drought severity during the Rabi season can be determined by the length of growing period (LGP). If the LGP in an area is very short (about 80-90 days), the area is likely to suffer very severe drought. With an increase of LGP by 10 days, the drought severity class changes from very severe to severe, from severe to moderate, from moderate to slight, and slight to no drought (Iqbal and Ali, 2001). Figure 24.2 presents the drought-affected regions of Bangladesh for the Rabi season. Iqbal and Ali (2001) categorized

Figure 24.2 A map showing drought-affected areas in Bangladesh during the Rabi cropping season.

drought on the basis of yield losses. Yield losses are 45-70% for very severe drought, 35-45% for severe drought, 20-35% for moderate drought, and 15-20% for slight drought. Table 24.2 gives a summary of affected areas under drought in the three cropping seasons.

Timing of planting is also a major factor in determining yield losses. The Bangladesh Rice Research Institute (BRRI, 1999) showed different levels of yields with respect to the planting dates for the variety Brridhan-29. If this variety was planted on July 15, the yield was 5.40 tons/ha after 148 days to maturity. If the same variety was planted on July 30, its growing period was reduced by only 3 days, but the yield loss was about 0.3 tons/ha. If the

Table 24.2 Summary of drought-affected areas by cropping seasons in Bangladesh

Area under various drought severity class (million ha)

Cropping season Very severe Severe Moderate Slight No drought Non-T. Aman

Pre-Kharif

Kharif (T. Aman only) Rabi

C.4C3 1.15 4.76 4.C9 2.C9 C.344 C.74 3.17 2.9C C.68 C.446 1.71 2.95 4.21 3.17

4.71

Source: Iqbal and Ali (2001).

planting date was August 30, the crop was forced to mature in about 128 days, resulting in a yield loss of about 28%.

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