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Compound drought and heatwave events in the eastern part of the Baltic Sea region

Klimavičius Laurynas, Rimkus Egidijus

Oceanologia

2024

Vol. 66 (1)

26--36

Droughts and heatwaves are natural phenomena that can cause severe damage to the economy, infrastructure, human health, and agriculture, among others. However, in recent years, it has been noted that their combined effect, known as compound drought and heatwave events (CDHE), often results in even greater harm. The main aim of this study was to identify CDHEs in this region during summers from 1950 to 2022 and assess the frequency and intensity of these events. To this end, the periods of droughts and heatwaves that occurred between 1950 and 2022 were determined, and the recurrence, extent, and intensity of these phenomena were evaluated. In this study, 1-month Standard Precipitation Index (SPI) values calculated for each summer day were used to identify droughts, while heatwaves were defined as a period of five or more consecutive days when the daily maximum air temperature (Tmax) was higher than the 90th percentile of Tmax. Precipitation and Tmax data (with a spatial resolution 0.25° x 0.25°) were obtained from the European Centre of Medium-Range Weather Forecast ERA-5 reanalysis dataset. The study showed that in most of the eastern part of the Baltic Sea region, the number of drought days had decreased from 1950 to 2022, while the number of heatwave days had increased significantly. In total, ten CDHEs were identified during the summers of 1950–2022. Eight of these events were recorded in 1994 or later. However, a statistically significant increase of CDHEs was found only in a small part of the study area.

Seasonality and long-term trends of NDVI values in different land use types in the eastern part of the Baltic Sea basin

Klimavičius Laurynas, Rimkus Egidijus, Stonevičius Edvinas, Mačiulytė Viktorija

Oceanologia

2023

Vol. 65 (1)

171--181

This study analyses changes in Normalized Difference Vegetation Index (NDVI) values in the eastern Baltic region. The main aim of the work is to evaluate changes in growing season indicators (onset, end time, time of maximum greenness and duration) and their relationship with meteorological conditions (air temperature and precipitation) in 1982–2015. NDVI seasonality and long-term trends were analysed for different types of land use: arable land, pastures, wetlands, mixed and coniferous forests. In the southwestern part of the study area, the growing season lasts longest, while in the northeast, the growing season is shorter on average by 10 weeks than in the other parts of the analysed territory. The air temperature in February and March is the most important factor determining the start of the growing season and the air temperature in September and October determines the end date of the growing season. Precipitation has a much smaller effect, especially at the beginning of the growing season. The effect of meteorological conditions on peak greenness is weak and, in most cases, statistically insignificant. At the end of the analysed period (1982–2015), the growing season started earlier and ended later (in both cases the changes were 3–4 weeks) than at the beginning of the study period. All these changes are statistically significant. The duration of the growing season increased by 6–7 weeks.