Table 6.3 indicates the lowest recorded rainfall in the 38-year period 1953-1990 was 703 mm
(1958). Based on the records, one can expect that the rainfall during the coming season will be
more than 703 mm as it was the lowest amount ever recorded. Note that all 38 monsoon seasons
had at least 703 mm of rainfall. The second driest monsoon rainfall on record was 772 mm in
1977. Out of 38 years, 37 years had at least 772 mm of rainfall. If the expectation is more than
703 mm, the chance declines considerably.
The same is true for the wettest year. The highest amount of rainfall recorded in the 1953-1990
period was 2 120 mm (1984). The second wettest year had 1 896 mm (1956). Interpreting this
indicates that the chance (probability) of getting at least 1 896 mm is only 5 percent. In
50 percent of the years, the rainfall was at least 1 377 mm. This further indicates that there
is only a 50 percent chance to receive 1 377 mm and above.
Extension personnel and farmers understand and regularly employ a range of drought
preparedness strategies. Climate forecasts decrease the risk of drought impact only when
uncertainty associated with forecasts is communicated properly. Failure to communicate or
understand the uncertainty of forecasts exposes users to excessive risk.
Figure 6.2 indicates the summer monsoon rainfall recorded at Dhaka in the 38 year-period from
1953-1990. The curve indicates that there is an extremely high chance of receiving the lowest
amount of rainfall. In other words, the chance of receiving 1 100 mm of rainfall is 88 percent,
while the chance of receiving 1 500 mm is only 22 percent