# Rainfall Erosivity Main Features and Their Associated Synoptic Conditions in North-Eastern Romania
## 3 Results and Discussions
### Synoptic Analysis of Days with Heavy Rainfalls
Figure 6: The share (%) of the three SOM synoptic patterns in the monthly heavy precipitation occurrence in the Moldavian Plateau between March and November (2013–2019). While the total precipitation amounts are not the highest among the three major weather patterns, the frequency and distribution of Type 1 events make it a critical factor in shaping the region's erosion dynamics. Additionally, the timing of these events during the warm season, when agricultural activities are at their peak, further amplifies their impact on soil stability and land management. The second most significant weather pattern (Type 2), accounting for 28.6% of heavy rainfall days, is characterized by the influence of Mediterranean cyclones that cross the Balkan Peninsula and propagate into the Black Sea region. This synoptic pattern is marked by a long-wave trough extending meridionally (north-south) across Romania in the mid-troposphere, while surface-level cyclonic conditions dominate the study area. This pattern is particularly active during the transitional seasons of spring and autumn, although the precipitation intensity per event is the lowest among the three major weather types identified (Figure 8). Figure 8: Seasonal hourly precipitation amount (mm) for the three SOM synoptic patterns associated with the occurrence of heavy precipitation in the Moldavian Plateau (2013–2019). Figure 7: Composite CAPE maps and mean vector wind for the three types of synoptic patterns (SOMs) associated with heavy precipitation in (2013–2019) in the Moldavian Plateau. The rainfall associated with this pattern is predominantly a frontal one, as evidenced by the consistently low CAPE values (Figure 7). Frontal precipitation bands are driven by a prevailing southerly wind flow, which transports moist air masses into the region. Daily precipitation records reveal a distinct maximum in north-eastern Romania (Figure 9), underscoring the importance of this weather pattern in causing consistent precipitation amounts fueled by humidity originating not only from the Mediterranean but also from the Black Sea region [61]. While the individual rainfall events under this pattern are generally moderate in intensity, their prolonged duration--often spanning a couple of days--can lead to significant soil erosion. This is particularly true in north-eastern Romania, where the combination of sustained rainfall and low vegetation cover during early spring exacerbates erosion risks. The lack of dense vegetation during this period reduces soil cohesion and increases susceptibility to erosion, as the protective effect of plant roots and canopy cover is minimal. Furthermore, the gradual saturation of soils over extended rainfall events enhances surface runoff, amplifying the erosive impact. This is proved by the fact that during two successive rainfalls events totaling 47 mm and 51 mm, respectively, occurred on 10-11 June 1980 and 22-24 July 1980, respectively, other studies reported a triple value of runoff and soil losses compared to individual rainfall of similar intensity [2]. The third major weather pattern associated with heavy rainfall (Type 3, accounting for 27% of events) is characterized by a persistent anticyclonic blocking system over northeastern Europe. This blocking pattern establishes a dominant easterly flow over northeastern Romania, which is frequently enriched with atmospheric moisture sourced from the northern Black Sea. In the mid- to upper troposphere, a long-wave trough channels cold air masses into the region, creating conditions of heightened atmospheric instability. This is reflected in the elevated CAPE values, particularly over the study area (Figure 7). The composite maps of this upper-level trough reveal the presence of cut-off low-pressure systems, which are typical under anticyclonic blocking conditions.