Coupled evolution of meteorological and hydrological drought until 2100 based on changes in climate scenarios

Drought affects all levels of the natural components of the system - from the atmosphere to upper layer of the lithosphere - and has a direct and indirect negative impact on ecological integrity, water resources, and socio-economic conditions. Therefore, analyzing this phenomenon requires a multi-scale temporal approach that accounts for the cumulative manifestations of meteorological and hydrological drought. The coupled evolution of meteorological and hydrological drought analysis was carried out, both at a historical level (for the period 1971-2020) and based on future climate scenarios (for the period 2021-2100), to highlight the vulnerability of a geographical area affected by these phenomena (the eastern part of Romania). Standardized meteorological (SPI and SPEI) and hydrological (SDI) drought evaluation indices were used for different time intervals (1, 3, 6, 9, and 12 months). The results align with regional observations on meteorological and hydrological drought patterns, highlighting sequences over last two decades characterized by extended drought periods, with observable impacts on river discharge. Bravais-Pearson correlation coefficients indicate strong links between meteorological and hydrological droughts (r ≈ 0.43-0.68), especially at the temporal scale of 9 and 12 months. The joint analysis of meteorological and hydrological drought evolution revealed a significant negative trend of frequencies, especially in the last twenty years.