Drought is a prolonged, continuous period of dry weather along with abnormal insufficient rainfall. It occurs when evaporation and transpiration exceed the amount of precipitation for a reasonable period. Drought causes the earth to parch and a considerable hydrologic (water) imbalance resulting in water shortages, wells dry, depletion of groundwater and soil moisture, streamflow reduction, crops withering leading to crop failure, and scarcity in fodder for livestock [1]. In the context of global warming, most of the climatic models project a decrease in precipitation in the dry season and an increase during monsoon in south Asia. This will cause a cruel combination of more extreme floods and droughts in the region. One of the aspects of global climate change scenarios in Bangladesh is the increased frequency and severity of droughts [2]. Drought is one of the most frequent natural disasters in Bangladesh which severely affect the agro-based economy and people's livelihood almost every year [3].  The country suffers from severe droughts at least once a decade. During the last 50 years, Bangladesh suffered about 20 drought conditions. Among them, droughts in 1951, 1957, 1972, 1979, and 1994 were very severe in nature, affecting more than 39% area of the country, and half of the population [1, 3].

In Bangladesh, drought is defined as the period when the moisture content of the soil is less than the required amount for satisfactory crop growth during the normal crop-growing season. The droughts in Bangladesh are mostly seasonal in nature. Bangladesh has a tropical monsoon climate characterized by wide seasonal variations in rainfall. Seasonal droughts occur due to a deficit of rainfall in a particular season. The water shortage due to the deficit of rainfall leads to streamflow reduction, and depletion of groundwater and soil moisture, and hence hampers crop growth and production [1, 3]. Drought mostly affects Bangladesh in pre-monsoon and post-monsoon periods. Two critical dry periods are distinguished. “Rabi” (December-February) as well as “Pre-Kharif” (March-May) drought occur due to: the cumulative effect of dry days; higher temperatures during pre- Kharif and low soil moisture availability. “Kharif” droughts in the period June/July to October, is created by sub-humid and dry conditions in the highland and medium highland areas of the country [3, 4].

Fig.1: Drought-prone areas in Bangladesh [1].

Droughts are common in the northwestern districts of Bangladesh (i.e. Barind Tract) in recent decades. Barind Tract covers most parts of the greater Dinajpur, Rangpur, Pabna, Rajshahi, Bogra, Joypurhat, and Naogaon. Rainfall is comparatively less in Barind Tract than in the other parts of the country. The average rainfall is about 1,971 mm, which mainly occurs during the monsoon. Rainfall varies aerially as well as yearly. For instance, rainfall recorded in 1981 was about 1,738 mm, but in 1992 it was 798 mm. The distribution of rainfall is rather variable from one place to another. Thus, this region has already been known as a drought-prone area of the country. The average highest temperature of the Barind region ranges from 35'C to 25'C for the hottest season and 12'C to 15'C for the coolest season. Generally, this particular region of the country is rather hot and considered a semi-arid region. Again, in the winter the temperature even falls at 5'C in some places in the Dinajpur and Rangpur districts. So this older alluvium region experiences the two extremities that clearly contrast with the climatic condition of the rest of the country [1].

However, drought can also occur in areas that usually enjoy adequate rainfall and moisture levels [1]. Inadequate pre-monsoon showers, a delay in the onset of the rainy season or early departure of the monsoon may create drought conditions in Bangladesh. The eastern part is prone to drought mainly because of rainfall variability in the pre-monsoon and the post-monsoon periods [4].

In Bangladesh, about 2.7 million ha are vulnerable to annual drought; there is about a 10% probability that 41-50% of the country experiences drought in a given year [5].  About 12.49 million ha of “Aman” rice cultivable land and 9.32 million ha of winter crop (Rabi crop) land area were affected by drought during the Pre-Kharif season and the Rabi season, respectively. Besides crops, droughts also affect orchards, forests, and the environment as a whole. Therefore, droughts are considered one of the key hindrances to ensuring optimum agricultural growth and achieving food security in Bangladesh [3].

Table 1: Major drought events in Bangladesh and impacts

Source: [1]

References

1. Banglapedia. Drought. Banglapedia: National Encyclopedia of Bangladesh. Dhaka, Bangladesh: The Asiatic Society of Bangladesh; 2021.
2. Shahid S, Behrawan H. Drought risk assessment in the western part of Bangladesh. Natural Hazards. 2008;46(3):391-413. doi: 10.1007/s11069-007-9191-5.
3. Alamgir M, Shahid S, Hazarika MK, Nashrrullah S, Harun SB, Shamsudin S. Analysis of Meteorological Drought Pattern During Different Climatic and Cropping Seasons in Bangladesh. JAWRA Journal of the American Water Resources Association. 2015;51(3):794-806. doi: https://doi.org/10.1111/jawr.12276.
4. Keka AI, Matin I, Rahman M, Banu D. Analysis of drought in Eastern part of Bangladesh. Daffodil International University Journal of Science and Technology. 2012;7(1):20-7. doi,
5. Tanner T, Hassan A, Islam K, Conway D, Mechler R, Uddin Ahmed A, et al. ORCHID: piloting climate risk screening in DFID Bangladesh. University of Sussex, UK: Institute of Development Studies; 2007.