Variability and Mechanisms of Megadroughts over Eastern China during the Last Millennium: A Model Study

Assessment of trends, variability and impacts of droughts across Brazil over the period 1980-2019

Drought indices are a numerical representation of drought conditions aimed to provide quantitative assessments of the magnitude, spatial extent, timing, and duration of drought events. Since the adverse effects of droughts vary according to the characteristics of the event, the socioeconomic vulnerabilities, exposed communities or environments, there is a profusion of drought indicators to assess drought impacts in different sectors. In this study, we evaluated the performance of two drought indices, the Standardized Precipitation Index-SPI and Standardized Precipitation Evapotranspiration Index-SPEI over Brazil derived from gridded meteorological information over the period 1980-2019. Firstly, we compared the gridded derived indices against the same indices derived from weather station data and available from a global dataset for time scales of 3, 6, 12, 24 months. Then we analyzed the spatio-temporal trends in SPI and SPEI time-series, which revealed statistically significant trends toward drier conditions across central Brazil for all time scales, though with more intensity for time scales of 12 months and larger. Trends were more significant in magnitude for SPEI than SPI, indicating an important role in the increase in evaporation, driven by increasingly higher temperatures. Finally, we demonstrated that climate signals are already having a disruptive effect on the country's energy security.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11069-022-05759-0.

The Influences of Tropical Volcanic Eruptions with Different Magnitudes on Persistent Droughts over Eastern China

In this study, the influences on persistent droughts over Eastern China from tropical volcanic eruptions with three categories of magnitudes, i.e., 25 Tg, 50 Tg, and 100 Tg, were investigated through three groups of volcanic sensitivity experiments based on the Community Earth System Model (CESM). The results showed that, the 25 Tg tropical volcanic eruptions are too weak to significantly influence the regional precipitation changes over Eastern China, while the 50 Tg tropical volcanic eruptions can strongly intensify droughts and prolong the drought conditions for about five years. Both the extension and intensification of the drought conditions induced by 100 Tg tropical volcanic eruption are the largest among the three sensitivity experiments. These drought conditions are mainly caused by the weakened East Asia Summer Monsoon (EASM), and their extension and intensification depend on the strength of the volcanic eruptions. The intensities of weakened EASMs after volcanic eruptions are associated with the distinct ocean–land thermal contrast after eruptions. The ocean–land thermal contrast is the largest after the 100 Tg tropical volcanic eruptions, while it is much weaker after the 25 Tg volcanic eruptions. The durations of drought extensions are determined by the recovery rates of the West Pacific Subtropical High (WPSH), which are associated with the magnitudes of the volcanic eruptions.

Extreme Drought Events over Brazil from 2011 to 2019

Drought-related disasters are among the natural disasters that are able to cause large economic and social losses. In recent years, droughts have affected different regions of Brazil, impacting water, food, and energy security. In this study, we used the Integrated Drought Index (IDI), which combines a meteorological-based drought index and remote sensing-based index, to assess the drought events from 2011 to 2019 over Brazil. During this period, drought events were observed throughout the country, being most severe and widespread between the years 2011 and 2017. In most of the country, the 2014/15 hydrological year stands out due to the higher occurrence of severe and moderate droughts. However, drought intensity and observed impacts were different for each region, which is shown by the different case studies, assessing different types of impacts caused by drought in Brazil. Thus, it is fundamental to evaluate the impacts of droughts in a continental country such as Brazil, where a variety of vegetation, soil, land use, and especially different climate regimes predominate.