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Rainfall, with its intensity, duration, and seasonal distribution, is among the main factors causing soil erosion, which is a widespread environmental problem in Bulgaria. Rainfall erosivity shows the potential of precipitation to generate erosion processes and is an essential indicator of the climate vulnerability of a region. This paper aims to evaluate rainfall erosivity in a part of the Eastern Rhodopes Mountains, an area that is characterised by high-intensity erosion processes and high erosion risk. Local peculiarities of rainfall erosivity were revealed by the calculation of some precipitation indices based on the monthly precipitation for the period 2000–2021, such as the precipitation concentration index (PCI), Angot precipitation index, Fournier index (FI), and modified Fournier index (MFI). The analysis of the extremely wet and extremely dry months at the annual and seasonal (October–March and April–September) levels was performed to evaluate the susceptibility to erosion. The results from the study show that rainfall erosivity in the studied area varies from low to moderate in the northern part of the study area and from high to very high in the south. According to the MFI, high and very high erosivities have been observed mainly since 2012. The erosivity increases from north to south, to the area with a complex relief, where the combination of orography and atmospheric circulation make favourable conditions for the occurrence of extreme precipitation. The analyses of the calculated indices show that the precipitations in most of the studied area generally have from a low to a moderate erosivity, but this does not exclude the occurrence of cases with high and very high erosivities, which are characteristic of recent years and are related to the increase in annual precipitations and extreme precipitation months. The results of this study can contribute to the development and implementation of measures and preventive activities for the reduction and possible elimination of the negative impacts of extreme precipitation. [ABSTRACT FROM AUTHOR]

Extreme weather and climate events have received increased attention in the last years due to their impact on different aspects of human activity. The aim of the present paper is to bring to better understanding of the causes of extreme precipitation occurrence in Bulgaria. An extreme precipitation month is defined as a month registering precipitation totals lower or higher than certain thresholds. Extremely wet months are defined as months with total precipitation amounts higher than 90% percentiles of the gamma distribution in the reference period 1961-1990. As extremely dry month, we consider the month with total precipitation lower than 10% of the gamma distribution. Spatial changes in the occurrence of extreme precipitation are investigated by the application of the cluster analysis. The circulation patterns were analyzed with regard to sea level pressure. The relation between the fluctuations of the extreme months and atmospheric circulation mechanism teleconnection is study by the North Atlantic Oscillation Indices (NAOI), the Eastern Atlantic pattern (EA) and the Mediterranean Oscillation Indices (MOI). [ABSTRACT FROM AUTHOR]