Trends in climate, short-duration rainfall, and damaging hydrogeological events (Apulia, Southern Italy)

This study analyses monthly climatic data (rainfall, wet days, rainfall intensity, and temperature) and the annual maximum of short-duration rainfall (from 1 hour to 5 days) to characterise climate variations, focusing on rainfall, and their effects on trends in damaging hydrogeological events (DHEs), defined as the occurrence of one or more simultaneous landslides and/or floods causing extensive damage. The methodology used is correlation, cross-correlation, trend analyses, and monthly indices. The monthly indices of rainfall, wet days, rainfall intensity, temperature, and flood and landslide occurrence were introduced to simplify the analysis of parameters characterised by spatial and temporal variability. The approach was applied to a region of southern Italy (Apulia). The data were collected from two databases: the damaging hydrogeological events database (1186 landslides and floods since 1918) and the climate database (from 1877; short-duration rainfall from 1921). A statistically significant decreasing trend in rainfall intensity and an increasing trend in temperature, landslides, and DHEs were observed. A generalised decreasing trend in short-duration rainfall was also observed. The main exception involved a very small number of time series with annual maxima as long as 6 hours, for which an increasing trend prevailed. The results concerning the trends of selected climate and short-duration rainfall characteristics did not justify the increasing trend in DHEs. Hypotheses justifying this increasing DHE trend are proposed. This article identifies the advantages of a simplified approach to reduce the intrinsic complexities of the spatial-temporal analysis of climate variability. This approach permits the simultaneous analysis of changes in flood and landslide occurrence.