A climatology and trend of hail events in Romania are presented using hail data spanning the years 1961–2014. Hail observations from weather stations and model reanalysis data were used to document the spatial and temporal distributions, variabilities, and environments of hail events. The results show that hail occurs most frequently in mountainous areas, while the smallest average number of hail days per year is found in the southeast. Herein, the convective season was defined as April–September, given that 94.2% of all mean monthly hail days were identified in this period. During the convective season the hail events prevail with most of these occurring in the afternoon and evening hours between 1000 and 1800 UTC. The severe hail events occur, overall, between 1400 and 1600 UTC, while in the southwest severe hail occurs later between 1600 and 1900 UTC. The spatial distribution of the convective parameters is consistent with the spatial distribution of hail days, revealing that hail is not favored in southeastern Romania, but in the rest of the country. The trend analysis of mean hail days per year disclose that 55.2% of all stations show a statistically significant upward trend, 3.8% show a statistically significant downward trend, while 40.9% show no statistically significant trend. A correlation between the variability of hail days per year and the variability in the occurrence of low pressure systems of Atlantic origin exists, the latter generating low pressure systems over the Mediterranean Sea that supply eastern Europe with the moist air needed for convection.

Severe storms that produce hail of significant amount or size carry a high risk, being responsible for damage at the ground. Hail spawned from these storms can affect crops, automobiles and buildings. A total of 52 hail events that occurred in May 2013 in southern Romania are used to investigate the relation between radar‐derived products and damage produced by hail. Two case studies are also presented to highlight the methodology used in this study.Three‐dimensional single polarization weather radar data were used to derive composite reflectivity, echo top heights, vertically integrated liquid, vertically integrated liquid density and hail kinetic energy flux to detect the hail clouds. Time integration and spatial distribution of these radar products were produced in order to capture the swath, intensity and longevity of the hailstorms. Hail and damage reports were used to link the radar variables to the effects of hailstorms at the ground. Hail size information was arbitrarily broken down into bins of reported hail to investigate the relation between hail size and radar parameters. The results show that the areas where hail and damage were reported are well captured by the footprints and magnitude of the radar variables. The average values of the radar parameters corresponding to hail size bins increase with the increase of hail diameter. A steeper increasing trend characterizes the vertically integrated liquid density and hail kinetic energy flux. The results show a good agreement between weather radar data and surface reports.

We evaluated the response of vegetation’s photosynthetic activity to drought conditions from 1998 to 2014 over Romania and the Republic of Moldova. The connection between vegetation stress and drought events was assessed by means of a correlation analysis between the monthly Standardized Precipitation Evaporation Index (SPEI), at several time scales, and the Normalized Difference Vegetation Index (NDVI), as well as an assessment of the simultaneous occurrence of extremes in both indices. The analysis of the relationship between drought and vegetation was made for the growing season (from April to October of the entire period), and special attention was devoted to the severe drought event of 2000/2001, considered as the driest since 1961 for the study area. More than three quarters (77%) of the agricultural land exhibits a positive correlation between the two indices. The sensitivity of crop areas to drought is strong, as the impacts were detected from May to October, with a peak in July. On the other hand, forests were found to be less sensitive to drought, as the impacts were limited mostly to July and August. Moreover, vegetation of all land cover classes showed a dependence between the sign of the correlation and the elevation gradient. Roughly 60% (20%) of the study domain shows a concordance of anomalously low vegetation activity with dry conditions of at least 50% (80%) in August. By contrast, a lower value of concordance was observed over the Carpathian Mountains. During the severe drought event of 2000/2001, a decrease in vegetation activity was detected for most of the study area, showing a decrease lasting at least 4 months, between April and October, for more than two thirds (71%) of the study domain.