What was done
The authors say "earth's climate is warming and will continue to warm in the future, as a result of changes in atmospheric CO2 and other trace gases," noting that model studies have suggested this phenomenon should lead to changes in rainfall intensity.  Hence, they analyzed rainfall data collected from 81 gauges spread throughout the Tuscany region of Italy for three different periods: (1) from the beginning of each record through 1994, (2) the shorter 1951-1994 period, and (3) the still-shorter 1970-1994 period.  For each of these periods, trends were derived for extreme rainfall durations of 1, 3, 6, 12 and 24 hours.

What was learned
For the period 1970-1994, the majority of all stations exhibited no trends in extreme rainfall at any of the durations tested; while four had positive trends at all durations and none had negative trends at all durations.  For the longer 1951-1994 period, the majority of all stations exhibited no trends in extreme rainfall at any of the durations tested; while none had positive trends at all durations and only one had negative trends at all durations.  For the still-longer complete period of record, the majority of all stations again continued to exhibit no trends in extreme rainfall at any of the durations tested; while none had positive trends at all durations and only one had negative trends at all durations.

What it means
Either (1) the climate of the Tuscany region of Italy just happens to be one that doesn't respond as climate models predict it should, or (2) the predictions of the climate models are wrong, or (3) earth's climate has not changed over the periods studied.