Cam here to say the same thing, the map appears to be overly smoothed and does not capture the sharp rainfall changes that often occur due to the local topography - e.g. when going from the windward side of a mountain to the leeward side.

For example, according to the map the rainfall at world's wettest place Mawsynram, is about 4300mm, which is about 35% of the the actual. https://en.wikipedia.org/wiki/Mawsynram