# Rainfall Erosivity Main Features and Their Associated Synoptic Conditions in North-Eastern Romania
## 3 Results and Discussions
### The Analysis of Hourly Precipitation Amounts
However, even extreme flash floods events have been characterized by hourly precipitation amounts of 35 mm [56], underlining the climatical relevance of our results. Overall, from our analysis, we can conclude that these record high values of hourly precipitation amount exceeding 40 mm have a low return period, so that their erosion potential is rather limited, being associated with rare and extreme erosion events and not with regular pluvial erosion conditions. Further, the values of hourly precipitation amount were classified by their intensity classes according to [PERSON] et al. [57]. The simplified classes used in this study are the following: \(<\)2.5 mm/h for light rain, 2.6-10.0 mm/h for moderate rain, and \(>\)10 mm/h for heavy rain. The hourly precipitation data from the two weather stations for 2013-2019 were then classified into one of the three types of rainfall intensity and the monthly frequency of this classes were calculated and represented as graphs (Figure 3). Firstly, it can be observed that most of the precipitation amounts below 2.5 mm/h (Figure 3a) fall in April, followed by March and November. Between 2013 and 2019, in April, at the Madarjac weather station, 56.7 h of light precipitation were recorded, while at the Carja weather station, 51.7 h of this kind were recorded. Conversely, in August, with reduced precipitation and increased rainfall intensity, the number of hours with light rainfall intensity was less than 20. The onset of the summer season is accompanied by an increase in atmospheric instability, leading to an elevated frequency of convective rainfall, particularly during the months of June and July. Conversely, August is marked by the predominance of dry periods, accompanied by a substantial decline in precipitation amounts. Consequently, June is observed to be the month in which the maximum number of hours with moderate precipitation (2.6 and 10 mm/h) is recorded (Figure 3b). Specifically, 6.7 h were recorded at Carja and 10 h at Madarjac, with the difference mainly attributed to the altitudinal difference. Heavy rains are relatively rare phenomena, usually occurring during intense convective processes. \begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Month/Year** & **2013** & **2014** & **2015** & **2016** & **2017** & **2018** & **2019** & _Average_ \\ \hline March & 0.06 & 0.14 & 0.07 & 0.04 & - & 0.13 & 0.03 & 0.08 \\ April & 0.10 & 0.13 & 0.04 & 0.31 & 0.06 & 0.10 & 0.10 & 0.12 \\ May & 0.26 & 0.39 & 0.05 & 0.09 & 0.10 & 0.08 & 0.20 & 0.17 \\ June & **0.45** & 0.20 & **0.16** & **0.32** & - & **0.56** & **0.33** & 0.34 \\ July & 0.14 & **0.42** & 0.02 & 0.17 & 0.17 & 0.20 & 0.09 & 0.17 \\ August & 0.17 & 0.10 & 0.08 & 0.21 & 0.15 & 0.07 & 0.16 & 0.13 \\ September & 0.08 & 0.07 & 0.11 & 0.13 & **0.37** & 0.07 & 0.31 & 0.16 \\ October & 0.02 & 0.09 & 0.06 & 0.15 & - & 0.04 & 0.13 & 0.08 \\ November & 0.09 & 0.05 & - & 0.07 & 0.03 & 0.01 & 0.01 & 0.04 \\ Annual average & 0.23 & 0.18 & 0.07 & 0.16 & 0.15 & 0.14 & 0.15 & 0.14 \\ Maximum/hour & 27.2 & 25.2 & 9.6 & 18.8 & 22.0 & 33.6 & 19.6 & 22.3 \\ \hline \end{tabular}
\end{table} 
Table 4: Maximum monthly precipitation intensity (mm/min) derived from hourly data during 2013–2019 at Madárjac weather station (bold italic indicates the monthly maximum). Heavy rains are uncommon for March-April and October-November, but are prevalent during the entire period from May to September. In these months, heavy rains occur, on average, for a duration of 0.5 h per year. As can be seen in the case of the analyzed area, precipitation with an intensity greater than 10 mm/h is specific to June at the two weather stations (Figure 3c). In Romania, convective rains are most frequent during early summer, particularly in June and July, across the hilly and plain regions east of the Carpathians. These rains are driven by both advective and local processes.