Drought is one of the most disastrous and costly natural hazards determined by a deficit of precipitation in a particular area. It causes large economic losses and affects access to water in various parts of the planet. Water scarcity impacts natural ecosystems and human activities dependent on water resources, especially crop production. Monitoring drought is therefore crucial to the evaluation of its impacts and to address the issue in a timely manner, in order to develop and implement mitigation measures. Various methodologies have been advanced to quantify essential drought characteristics, such as time of onset and ending, duration and intensity. The objective of this paper is to review the existing indices used for drought identification and assessment and to propose an index typology. The study employs bibliographical research, synthesis and classification of indices by data source input and their aims. The results provide a brief overview of the drought indices based on measured or modelled data (meteorological, hydrologic or agricultural approaches), remote sensing data (hydrometeorological or ecological approaches) and multivariate or composite indices.

A diachronic analysis of the geomorphic units using a geographical information system (GIS) that integrates historical maps, aerial and satellite imagery is a useful method to explore fluvial morphodynamics. This study used the mentioned spatial data sources to investigate the morphological changes of the islands on the Low Danube River between Călărași and Cernavodă between 1864 and 2016. At the same time, the accuracy of the cartographic materials was evaluated to differentiate between real change caused by identification or positional errors. There is a general increase in area and number of islands in the study area in the context of decreasing sediment volume transported by the Danube.

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This study investigates the drought trends and their spatial variability in southeastern Romania, based on the Standardized Precipitation Evapotranspiration Index (SPEI) analysis (for 1, 3, 6 and 12 months), by using E-OBS precipitation and temperature gridded data between 1950-2018. Trends in the variability of SPEI are analyzed using the Mann-Kendall non-parametric test with the Theil-Sen method for slope estimation. Results show increasing wetness in autumn and dryness during the other seasons for SPEI at 3 months scale, with significant negative trends in winter at the higher altitudes in the study area and in the Danube Delta. SPEI cumulated for 6 months in September shows dryness trends over most of the study area, while SPEI for 6 months in March shows dryness trends only over the western part of the studied region. The results can be useful for designing or improving the regional adaptation practices in order to reduce the negative consequences of droughts in areas affected by drought intensification tendencies.