In the analysis of flood statistics, one should always have recourse to comparisons of reconstructions of precipitation intensity. Increased flood situations, in addition to frequent heavy rain, may have completely different reasons, such as river regulation and the reduction of flood areas. Such anthropogenic activities lead to the construction of large tidal waves that sweep down rivers with high speed and initiate new flood records, although the climate-related rainfall may not have even increased.
In the International Journal of Climatology in mid-2011, a study of an Italian research team headed by Yuri Brugnara, in which the authors studied 200 precipitation records from northern Italy going back 90 years. The scientists determined the development of total precipitation ( total precipitation, TP), the number of wet days (wet days, WD) and precipitation intensity (precipitation intensity, PI). The corresponding curves are shown in Figure 1. Surprisingly, none of the investigated parameters of precipitation have increased. If anything, there is a slightly negative trend over the past 90 years in the record. The simplistic concept of increased flooding caused by global warming will obviously not apply in Northern Italy.
Figure 1: Development of three rainfall parameters in northern Italy during the last 90 years. Total precipitation (total precipitation, TP), number of wet days (wet days, WD), precipitation intensity (precipitation intensity, PI). From Brugnara et al., 2011.