“One night I learned that a hailstorm was forecast on TV to hit a nearby area that night, and it came to happen. But early the next morning, we found that it had also hit our area, which was totally unexpected. The paddy, which was about to ripen and was just four days from harvest, was destroyed…”
This is part of a story from a Sylhet rice farmer. His Boro rice crop was destroyed by a hailstorm that happened during the summer months (March-May), before the monsoon. The hail that destroyed his crop was the result of moist air rising in the atmosphere, otherwise known as convection.
This convection also causes heavy rainfall and flash floods during the same period. These summer weather events obviously impact the life of the farmer we spoke to, but is this true for many other people in the Sylhet region?
As part of the ongoing TRACKS climate research project, we spoke to more than 230 people in the Sylhet region and many agreed; the rain during the summer months is very important. Many farmers told us that the flash floods could potentially destroy their crops and damage their property. On the positive side, the floods can fill in the haors, so that fishing can begin. Whether the impacts are positive or negative, the summer rainfall has significant impacts on the livelihoods of the people in northeast Bangladesh. This is an important message for climate researchers, and in particular, the researchers in the TRACKS project.
In the TRACKS project, we directed our research to investigating rainfall and convection during the period of March-May. This period is an interesting one for the climate scientists. It is interesting because the answers to many weather-related questions remain elusive.
We still don’t completely know what causes the rainfall in northeast Bangladesh at this time of year. A number of researchers in Bangladesh and abroad have published theories about what causes this rainfall. Several of these theories connect the rainfall with the air rising over the Meghalaya’s.
Other theories discuss the impact of differences in air humidity; the air over Bangladesh is moist during this period, whereas, over India, the air is very dry. All the theories published in the scientific literature seem robust. The interesting thing is that they all might be correct. It is very likely that all these different mechanisms interact and influence each other.
To see if this is correct, we need weather observations and measurements. There are rainfall observations from the Bangladesh Meteorological Department and Bangladesh Water Development Board that we can use. These datasets provide an excellent picture over time to help us understand local climate and how it varies. However, to understand what actually causes the rainfall in the summer months, we need high-resolution information, which also extends upwards in the atmosphere.
To get this type of information, we use weather models to simulate the weather and rain over Sylhet for April several years in a row. The model we use is called WRF (Weather Research and Forecasting model) and is also used by the Bangladesh Meteorological Department to make forecasts.
At the moment, we are in the process of analyzing this information and running more simulations. We hope that we will be able to shed light on some of the causes of the summer rainfall in Sylhet Division and that these findings might help forecasting efforts in the region. All of our simulations will be made available to the research community in Bangladesh and, in particular, the Bangladesh Meteorological Department.
Who knows, we may add another theory to the list of causes for the summer rainfall in the Sylhet region. Whatever happens, we are certain that we are doing science that is driven primarily by the stories that we heard from the local people in Sylhet.
If we want to do climate science that makes an impact at the local level then we have to try and understand what the issues are at the local level. We can gain this understanding by listening to the stories of people like the rice farmer who lost his crop to the hailstorm.