Bangladesh, straddling the Tropic of Cancer, has one of the wettest climates in the world, and about 80% of it’s rain falls during the monsoon season, characterized by high temperatures, high humidity, and of course…heavy rainfall. But this year the monsoon failed to arrive on time, typically expected in early June, delaying its initial downpour until the final few days of the month.
The monsoon continues in Bangladesh until the end of September, but it is in the month of June, with an average rainfall of nearly 460 millimeters that it normally delivers its heaviest showers. This year the Meteorological Society have recorded less than half of that average, and this will directly impact the rice yield, Bangladesh’s staple crop.
There are typically two main varieties of rice planted here, Aman and Boro. Aman accounts for nearly a third of Bangladesh’s annual output, and needs to be planted in mid-July. It is the Boro which relies so heavily on irrigation to bring the crop through, and has this year frequently required the diversion of electricity away from the power-hungry cities, contributing to their frequent blackouts.
During the annual monsoon period, the rivers of Bangladesh flow at around 140,000 cubic meters per second, as compared to a diminished 7,000 cubic meters per second during the dry season, and with agriculture depending so heavily on natural irrigation due to the fierce competition for electrical power, more than 60 % of the net arable land, some 91,000 km², is cultivated during the rainy season despite the possibility of severe flooding.
The monsoon is created from the contrast between low and high air pressure areas, resulting from the differential heating of land and water. During the high temperate months of April and May hot air rises over the Indian subcontinent, creating low-pressure areas into which cooler, moisture-bearing winds from the Indian Ocean then rush, called the southwest monsoon.
Dividing against the Indian landmass, the monsoon flows in two branches, one of which strikes western India. The other travels up the Bay of Bengal and over eastern India and Bangladesh, crossing the plain to the north and northeast before being turned to the west and northwest by the foothills of the Himalayas.
But as relieved as everyone appears to welcome the final arrival of this slow monsoon, there is a potential darker side. Annual flooding can result in the loss of human life, damage to property and communication systems, and a shortage of drinking water, which in turn can lead to the spread of disease. So, as I have often found here in Bangladesh, things can turn on a bitter sweet balance. Finally we have our vital rainfall, but what course this complex weather system will take over the coming months remains to be seen.