Exploring Precipitation Intensity-Duration-Area-Frequency Patterns using Weather Radar Data

Extreme precipitation is the main trigger of hazardous phenomena such as floods and flash-floods, that pose a serious threat to human beings and livelihood worldwide. Extreme precipitation is highly variable in both space and time, thus understanding and managing the related risks necessitates improved knowledge of their probability at different spatial-temporal scales.

We employ the simplified metastatistical extreme value (SMEV) framework, a novel non-asymptotic framework, to estimate extreme return levels (up to 100 years) at multiple temporal (10 min–24 h) and, for the first time, spatial (0.25 km²–500 km²) scales using weather radar precipitation estimates. The SMEV framework reduces uncertainties and enables the use of relatively short archives typical of weather radar data (12 years in this case).

Focusing on the eastern Mediterranean - a region characterised by sharp climatic gradients and susceptibility to flash floods - we derive at-site intensity-duration-area-frequency relations at various scales. Comparison with extreme return levels derived from daily rain gauge data over areas with dense gauge networks yields comparable results, demonstrating that radar precipitation data can provide important information for the understanding of extreme precipitation climatology.

We then examine the climatological differences in extreme precipitation emerging from coastal, mountainous, and desert regions at different spatial and temporal scales. Three key findings emerge:

• At the pixel scale, precipitation and duration exhibit simple scaling, but this relationship breaks down with increasing area - this has significance for temporal downscaling.
• Precipitation intensity is dissimilar for different area sizes at short durations but becomes increasingly similar at long durations - thus areal reduction factors may be unnecessary when computing precipitation for long durations.
• The reverse orographic effect causes increased precipitation for multihour events and decreased precipitation for hourly and sub-hourly durations; however, this phenomenon decreases over larger areas.