Investigation of the spatial and temporal distribution of heavy rainfall in Attica

The present graduate study examines the time and spatial distribution of intense rainfall in different scales (both in time and space). The study area is located in the watershed of Kifisos River of Attica in Greece, where a dense network of rain gauges (METEONET), which provides data of small time scale, is planted. The management and processing of rainfall data was performed using the GIS (ArcMap), which enables direct monitoring of temporal evolution and spatial distribution of rainfall. Rainfall events that were the most intense, considering the maximum rainfall and the duration of the entire episode, were selected. The point rain heights were later converted into surface rainfall using the deterministic method of spatial interpolation Inverse Distance Weighted (IDW). As a result rainfall surfaces of different temporal and spatial scales were formed. Thus, it was possible to estimate the maximum rainfall for each spatial and temporal scale studied. Moreover, some episodes were studied in terms of temporal variability. Based on the exported data, the areal reduction factor (ARF) was estimated for the various temporal and spatial scales and was compared with the corresponding empirical factor in bibliography. The reduction factor derived from this analysis shows a power–law decay with respect to the area of integration and the duration of the storm. A weak, but significant decrease of the areal reduction factor with respect to the return period is also shown and this result is consistent with that of some recent studies on this topic. Equations, that show the relationship between the ARF and the intensity of rainfall for the study area, were made. Finally, a function was developed, that relate the rainfall intensity over an area and a duration with the frequency of occurrence. The curves that describe this relation are known as intensity–duration–area–frequency (IDAF) curves. This is a first approach, which requires more careful and thorough further investigation. A more extensive analysis of observed rainfall fields is needed, to state the dependence. The results obtained are preliminary but important and can find useful applications.