Drought with its occurrence and manifestations at all levels of the natural components, yields both direct and indirect negative effects, on the ecological systems, water resources, social, as well as economic aspects of life. Therefore, any analysis that concerns this phenomenon, must be carried out at a multi-scalar level, addressing all manifestation levels (meteorological, hydrological, and hydrogeological drought). Standardized evaluation indices (for precipitation-SPI, evaporation-, -SPEI, streamflow-SDI and groundwater-SGI) have been used to analyze the evolution of the drought phenomena in Eastern Romania, for 1, 3, 6 and 12 months’ time-scales, applied to seven groundwater bodies. The results of the analysis complement the observations concerning the evolution of meteorological drought (using SPI and SPEI) in the East European region, by highlighting the drought sequences of the last two decades of the last century. Those are accompanied by the meteorological drought sequences which occurred on extensive areas, starting from 2007, until present, with direct effects in river discharge and increases in groundwater level depths. The Bravais–Pearson correlation coefficient shows a close connection between meteorological and hydrological drought (r ~ 0.45 to 0.68) and between hydrological and groundwater drought (r ~ 0.42 to 0.74) for wells with piezometric level under 5 m depth. In the larger context of climate scenarios which envision an increase in air temperature, and a decrease in the atmospheric hydrological input, the increase in the drought frequency is obvious, with direct effects on all-natural components that are dependent on the hydrological resources.

The evolution of groundwater levels is difficult to predict over medium and long term in the context of global climate change. Innovative trend analysis method (ITA) was used to identify these trends, and ITA index was calculated to measure their magnitude. The data used are sourced from 71 hydrogeological wells that were dug between 1983 and 2018 and cover an area of over 8000 km² developed in the temperate continental climate in the north-eastern part of Romania. The results obtained by applying the ITA show a general positive trend for groundwater level over 50% of wells for winter and spring seasons and annual values. The negative trends were observed for more than 43% of wells for the autumn season followed by the summer season (less than 40%). The magnitude of trends across the region shows a significant increase for spring season (0.742) followed by winter season (0.353). Important changes in the trends slopes and magnitudes have been identified for groundwater level depth between 0 and 4 m (for winter and spring seasons) and between 4 and 6 m (for summer and autumn seasons). The results can be implemented in groundwater resources management projects at local and regional level.

Groundwater resources from a region may be subject to complex human and climatic pressure. The present study tries to analyze the human and climatic pressure on the groundwater resources from the eastern part of Romania, between 1983 and 2017, for seven groundwater bodies. Two parameters, the groundwater exploitation index (GWEI) and the Standardized Groundwater Index (SGI) for identifying hydrogeological droughts, were used to assess human and climatic pressure. The high values of GWEI show a significant increase in human pressure on water resources in recent decades, in lower and more populated areas, from the south and north part of de region, amid increasing investment in agriculture. In the case of climate pressure, the SGI values show significant values for the years 1983, 2000, 2007, and 2012. However, the overlap of hydrogeological droughts with an increase in human pressure can have a significant impact on the groundwater resources from this region, with negative effects in the mid and long term, under the growing effects of the regional climate changes.

Hydrological vulnerability (HV) is a (changing) underlying condition in all drainage basins, depending on the dynamics of the potentially dangerous hydrological phenomena, the particularities of drainage networks, land use patterns, and processes that shape landforms in extensive periods. The socioeconomic attributes and the hydrotechnical infrastructure add up to the manifestation of this type of vulnerability. In this paper, we assess the HV levels of 81 drainage basins in the NE of Romania for three distinctive periods (1990–1999, 2000–2009, 2010–2018), using a multi-criteria approach. Two classical multi-criteria decision making (MCDM) methods were combined in order to evaluate the HV according to factors that refer to floods and hydrological drought occurrences, hydrotechnical structure coverage, the drainage network, land use, and landforms characteristics. The Analytic Hierarchy Process (AHP) was applied to weigh these factors and the resulting relative importance values were integrated in the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS), by which the alternatives represented by the catchments were ranked. The attenuation of the HV through time follows an East–West direction, from the lower elevations of the Moldavian Plateau to the heights of the Carpathians. Hydrological droughts are more likely to occur in the Eastern part of the analyzed territory, while the western section displays a certain propensity for floods. The results may be used by local and national authorities in order to improve the hydrological risk mitigation strategies, and to develop more targeted water management projects, properly calibrated to the conditions of the Northeast Development Region in Romania.

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.