Precipitation

Trends within Varibility

Climatological averages and trends need to be seen relative to the inter-annual variability

Change and Significances

Trends determined on different length of timeseries can be a good indicator of change. A period dominated by natural variability (low trend) can be seen in contrast to the emergence of an (anthropogenically) forced trend.

Future changes and scenarios

In the long term, average amounts of precipitation in the summer months will shrink, and evaporation will increase. The ground will become drier, there will be fewer rainy days and the longest precipitation-free period will last longer.

Bangladesh’s NC3 also reports that no statistically significant changes in historical average annual precipitation have been measured. However, over the period 1975–2003, changes in the seasonality of precipitation were significant, with increases in the post-monsoon season in the range of 5–15%, and decreases in the pre-monsoon season that typically less than 5%.

Seasonal Cycle Showing the Projected Average Monthly Precipitation for Bangladesh for the Period, 2040–2059, in Relation to the Historical Reference Period, 1986–2005, RCP8.5

Trends in future precipitation in Bangladesh are highly uncertain. As shown in Figures 4 and 8, the model ensemble’s most common estimate is of a slight increase in average precipitation. However, the response of precipitation to higher emissions pathways appears not to be a simple linear relationship with temperature change. Future changes will likely depend both on climate change influences on monsoon rainfall patterns and on tropical cyclone activity. These are currently uncertain. Work by Jayasankar et al. (2015) aimed to identify the best performing sub-group of models for simulation of future monsoon rainfall changes.31 Their favored models point towards a slight reduction in the frequency of future light precipitation events which is offset by an increase in the frequency of high and extreme precipitation events. In fact, thereis agreement among the available studies that highertemperatures will increase evaporation and atmospheric moisture, leading to increases in the intensity of extreme precipitation events in the South Asian Monsoon.32 This finding is in keeping with global-climate modelling. The intensity of sub-daily extreme rainfall events appears to be increasing with temperature, a finding supported by evidence from different regions of Asia.

	RCP 2.6	RCP 4.5	RCP 8.5
Possible around mid-century	1.1( -1.3, 3.7)	1.5 (-0.9,3.9)	1.9 (-0.5, 4.4)
Possible by the end of the century	1.2 (-1.3, 3.8)	2.2 (-0.3, 4.9)	3.9 (1.4, 6.7)

A noticeable reduction in precipitation during the summer months is expected in the future. Although we are still experiencing a similar amount of rainfall on an average rainy day in summer as in the past, there are now more days without rain. The longest dry period in summer may last about a week longer on average by the middle of the century.

A noticeable reduction in precipitation during the summer months is expected in the future. Although we are still experiencing a similar amount of rainfall on an average rainy day in summer as in the past, there are now more days without rain. The longest dry period in summer may last about a week longer on average by the middle of the century.
A noticeable reduction in precipitation during the summer months is expected in the future. Although we are still experiencing a similar amount of rainfall on an average rainy day in summer as in the past, there are now more days without rain. The longest dry period in summer may last about a week longer on average by the middle of the century.
A noticeable reduction in precipitation during the summer months is expected in the future. Although we are still experiencing a similar amount of rainfall on an average rainy day in summer as in the past, there are now more days without rain. The longest dry period in summer may last about a week longer on average by the middle of the century.