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.

RESUMO As inundações sem precedentes de abril a maio de 2024 no Rio Grande do Sul afetaram mais de 90% do estado, deslocando centenas de milhares de pessoas e causando 172 mortes. O fenômeno El Niño Oscilação Sul foi considerado importante para explicar a variabilidade nas chuvas observadas, consistente com pesquisas anteriores que mostram que eventos anteriores de fortes chuvas na área ocorreram durante anos de El Niño. As frentes frias que trazem chuvas permaneceram estacionadas no sul do Brasil, uma vez que não puderam se mover para o centro do Brasil devido ao bloqueio atmosférico com ar quente e seco e às temperaturas mais altas naquela região. A inundação em Porto Alegre foi desencadeada por fortes chuvas na Bacia do Guaíba, com acumulações superiores a 500 mm em 5 dias, levando a níveis recordes de 5,35 m em 5 de maio, valores mais altos que a enchente anterior, em 1941. Além do caráter extremo deste evento, isso contribuiu para os impactos significativos de enchentes em áreas vulneráveis da Região Metropolitana de Porto Alegre e municípios próximos. Isso mostra a necessidade de avaliar objetivamente o risco e reforçar a infraestrutura para inundações para aumentar a resiliente a esta e futuras enchentes, ainda mais extremas.

Soil moisture over the Brazilian semiarid region is presented in different visualizations that highlight spatial, temporal and short-term agricultural risk. The analysis used the Soil Moisture Index (SMI), which is based on a normalization of soil moisture by field capacity and wilting point. The index was used to characterize the actual soil moisture conditions into categories from severe drought to very wet. In addition, the temporal evolution of SMI was implemented to visualize recent trends in short-term drought and response to rainfall events at daily time steps, as new data are available. Finally, a visualization of drought risk was developed by considering a critical value of SMI (assumed as 0.4), below which water stress is expected to be triggered in plants. A novel index based on continuous exposure to critical SMI was developed to help bring awareness of real time risk of water stress over the region: the Index of Stress in Agriculture (ISA). The index was tested during a drought over the region and successfully identified locations under water stress for periods of three days or more. The monitoring tools presented here help to describe the real time conditions of drought over the region using daily observations. The information from those tools support decisions on agricultural management such as planting dates, triggering of irrigation, or harvesting.