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Extreme Rainfall Analysis

The Maproom facilitates the exploration of the history of extreme monthly and seasonal rainfall characteristics.

The user can define the Season and Seasonal Daily Statistics of interest and then map the probability of non-/exceeding a user-defined threshold. The map therefore illustrates how likely or unlikely the threshold is to be crossed. The user can also look at the variance or coefficient of variation of the seasonal quantity to get a sense of the range of variability across the years. Clicking on the map will then produce the probability of exceeding graph represented by a normal distribution. The graph gives a sense of the range of possible value for the seasonal characteristics of interest, including its extreme values. The different options are detailed below.

Season: Specify the start and end dates of the season , over which the rainfall characteristcs are to be computed over the full range of years of data available (1981-2017).

Wet/Dry Day/Spell Definitions: These define the amount in millimeters (non inclusive) above which a day is considered to be a wet day (as opposed to dry), and the minimum number (inclusive) of consecutive wet (dry) days to define a wet (dry) spell.

Seasonal daily statistics: Choose the seasonal diagnostic quantity (i.e the statistic of the daily data) to be computed for each season, from the following choices.
Total Rainfall: total cumulative precipitation (in mm) falling over the season.
Number of Wet Days: the number of wet days (as defined above) during the season.
Number of Dry Days: the number of dry days (as defined above) during the season.
Rainfall Intensity: the average daily precipitation over the season considering only wet days.
Number of Wet (Dry) Spells: the number of wet (dry) spells during the season according to the definitions above. For example, if a wet spell is defined as 5 contiguous wet days, 10 contiguous wet days are counted as 1 wet spell. Note that a spell, according to the definitions above, that is overlapping the start or end of the season will be counted only if the part of the spell that falls within the season reaches the minimal length of consecutive days.

Yearly seasonal statistics: choose the threshold to map the probability of non-/exceeding, or look at the variance or the coefficient of variation of the yearly seasonal time series across the 1981-2017 period.
Probability of non-/exceeding: the portion of years, in percentage, when the seasonal quantity exceeded or not a given threshold.
Variance: a measure of the variability of the seasonal quantity, expressed in square of the units. The higher, the farther the quantity departs from its mean value.
Coefficient of Variation: the ratio between the standard deviation (square root of the variance) and the mean of the seasonal quantity. It gives similar information as the variance but in perspective with the value of the mean rather than in units of the quantity.

Spatial Resolution: The analysis can be done and mapped at each 0.05˚ resolution grid point. Additionally it is possible to average the daily rainfall, prior to doing the analysis, over the 0.05˚ grid points falling within administrative boundaries for the probability of exceeding graph.

Dataset Documentation

Reconstructed rainfall on a 0.05˚ x 0.05˚ lat/lon grid from the Bangladesh Meteorological Department. The time series (Jan 1981 to Aug 2018) were created by combining quality-controlled station observations in BMD’s archive with satellite rainfall estimates.

How to use this interactive map

Helpdesk

Contact BMD with any technical questions or problems with this Map Room.

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