Last month I posted a complete log of days at Manilla that had more than 50 mm of rainfall.
I call days that have more than 50 mm of rainfall “very wet days”. At Manilla, on the average, these have come only once per year. Days with more than 50 mm of rainfall have no special meaning, but they can be taken as a rough indication that local flooding, or even general flooding, is likely: the “Flooding Rains” of Dorothea Mackellar.*
The graph I posted did not show whether these very wet days, likely to cause floods, had a bigger effect at some times than at others. This graph shows that.
Since it is only the excess rainfall that runs off, leading to flooding, I have subtracted 50 mm from each “very wet day” rainfall amount. Then I have summed all such excesses for each half-decade. I summed the half-decades in pairs to give a decade sum (in mm) centered on the years 1885, 1890, 1895, etc. For example, the decade centered on 1925 had a total of daily rainfall excesses of 157 mm. (Values for 1880-84 were estimated from those for 1883 and 1884.)
Some decades had very high values of excess rainfall: there was about 250 mm in the decades centered on 1900, 1960, 1965, 1980, and 2000. There were very low values, below 100 mm, in the decades centered on 1885, 1890, 1950, and 1990. There appears to be no trend.
Note added June 2015.
The close similarity of two graphs, the one of heavy rainfalls in this post, and the one of year-long droughts in an earlier post led me to write a further series of three posts:
More droughts After Heavier Rains I.
More droughts After Heavier Rains II.
More droughts After Heavier Rains III.