Not sure how much an effect a long dry spell would have on water levels in a mine, as they tend to be flooded due to the ground water rather than a through flow, probably talking inches which the photo shows.
We were given the task many years ago to survey a cave system as it had never been surveyed and a housing estate was to be built above. Was sent in after a very dry month in August when the stream flow was greatly reduced. Had been told a through trip was possible as it had been done before. Alas we bailed after surveying about 60% of it as it was tight and even with a low flow many sections were flooded to almost roof level.
Researching the system afterwards we found out it had had only been done end to end the once, this was in 1961 after the feeder stream had frozen solid so there was no water flow.