# Rainfall Erosivity Main Features and Their Associated Synoptic Conditions in North-Eastern Romania
## 1 Introduction  
Soil erosion represents a critical global issue, posing a significant threat to food security, ecosystem stability, and sustainable land management, particularly in vulnerable regions worldwide [1]. Rainfalls are recognized as one of the primary drivers of soil erosion [2, 3], with their role being extensively documented in recent studies [4, 5]. In addition, the contribution of extreme wind events to soil degradation has gained increasing attention, particularly in arid and semi-arid regions, where their impact rivals that of rainfall [6, 7]. However, water, whether from rainfall or snowmelt, remains the dominant morphogenetic agent, shaping landforms and driving the dynamic evolution of slopes through a diversity of processes such as sheet, rill, and gully erosion [8, 9, 10]. Rainfall aggressiveness is the most appropriate parameter through which the erosion capacity of a torrential rainfall can be determined. Erosion is triggered by the energy shockcaused by torrential rains, but also by the quick organization of the liquid runoff. Rainfall erosivity expresses the ability of liquid precipitation to have a significant erosion impact. This parameter is defined most frequently as rainfall index, representing the product of the kinetic energy of a rainfall and its intensity calculated over a period of 30 min [11]. Due to the difficulties of calculating this index, caused by the scarcity of the precipitation data at sub-hourly level, it is important to mention that rainfall aggressiveness is often expressed by other methods that are easier to apply. Even if their accuracy is lower, some of them have a higher suitability for generalizations and synthesis studies at regional level [12]. Overall, rainfall aggressiveness follows an annual cycle [13], driven by combined climate conditions and land use/cover seasonality, being conducive to a plethora of complex environmental and agricultural problems. These include the degradation of the physical, chemical, and biological properties of the soil [14], accelerated nutrient depletion [15], and reduced agricultural productivity [16], which is projected to worsen under future climate scenarios [17]. Recent research has also highlighted the compounding effects of land use change and intensifying extreme weather events, which exacerbate erosion rates and threaten long-term cropland viability [18]. In Romania, the alternation between prolonged droughs and heavy rainfall periods has also led to significant disruptions in the multiannual climate pattern over large areas, resulting in changes in the frequency and intensity of extreme climate events such as heavy precipitation [19; 20]. Also, these sequences of severe rainy periods with dry ones are increasingly damaging to agriculture, one of the main economic fields of the country. Thus, land degradation under both climate change and human impact has been recognized as a major environmental threat, especially in the Moldavian Plateau of northeastern Romania [21]. Under these circumstances, estimation of rainfall aggressiveness could contribute to a more accurate assessment of soil loss through erosional processes that, consequently, lead to proper agricultural land use patterns in accordance with best sustainable management practices. Besides the general very good and extensive knowledge on the topic of soil erosion induced by rainfall aggressiveness, the atmospheric conditions associated with this environmental issue have not been extensively previously investigated. Even if the synoptic conditions associated with atmospheric instability or nail occurrence [22] are well understood for northeastern Romania and can serve as proxies in understanding the synoptic conditions associated with soil erosion, the need for an applied study on this topic is high and therefore the presented study is meant to respond to this need.