Heavy rainfalls in Bulgaria due to solar activity and their possible influence on landslides

Summary The solar activity cycles affect various parameters of surface areas, including rains, snow covers, river streamflows and other hydrological cycles. These processes are due mainly to the total solar irradiance variations, followed by weather and climate changes. The interconnection between the solar cycles and decadal changes of rainfalls over Bulgaria is investigated by means of reconstructed Total Solar Irradiance TSI, precipitation from meteorological stations Sofia, Varna, and Palmer Drought Severity Index (PDSI) for the period 1899–2015. The decadal oscillations of precipitation and TSI with periods corresponding to the sunspots (11 years), solar magnetic cycle (22 years), equatorial solar asymmetry (45 years), Gleissberg cycle (70–100 years) and their harmonics are compared and analyzed. Models of decadal variations of PDSI and precipitation, based on solar cycles and harmonics, are created. The periods with rainfall and PDSI maxima are calculated on a century time span and a forecast of landslides is determined.