Índice de exposição à ação das secas meteorológicas: NIFT (Number/Intensity/Frequency/Trend) Index

Abstract

Drought is a natural phenomenon, originated from the absence of precipitation over a certain period, capable of causing damage to different sectors of society. Thus, monitoring the spatiotemporal behavior and the level of exposure to the action of this phenomenon is a task of extreme importance for water resource management. In this sense, the objective of this work is to develop an index to quantify the level of exposure to the action of meteorological droughts: the NIFT (Number/Intensity/Frequency/Trend) Index. For its creation, ten parameters were used, which include information related to the quantity, intensity, frequency, and trends of droughts (behavior, duration, and severity) computed based on the Standardized Precipitation Index (SPI). Three thousand and ninety precipitation series from the Global Precipitation Climatology Centre (GPCC) distributed throughout Brazil over 50 years (1970–2019) were used, and the analyses were carried out at two spatial scales (grid and regional) and four temporal scales (monthly, quarterly, half-yearly and annual). Hierarchical cluster analysis procedures were applied to identify zones with similar behaviors, and the relationship between the level of exposure and the physical characteristics of each region was investigated using the Fisher test. The results show high variability in the spatiotemporal behavior of precipitation, such that the Northern region is the rainiest in Brazil, while the Central-West, Southeast, and Northeast regions are less rainy. Moreover, the characterization of drought events indicates that the number and average intensity of events are higher at the monthly and quarterly levels, while events are longer and more severe at the half-yearly and annual levels. Additionally, the data indicate that several regions have been affected by severe drought events in recent years, and the trend is for these events to be more frequent and significant in much of the country. The results indicate that the Northeast is the region with the highest level of exposure to the action of meteorological droughts, especially at the quarterly and half-yearly levels. The results of the hierarchical cluster analysis reveal high variability in the regionalization relative to the level of exposure to the action of droughts, but the pattern of the Northern and Southern regions differs from the other regions. Finally, the relationship between the NIFT values and the characteristics of each region suggests that areas with high precipitation variability have higher levels of exposure, while higher and rainier regions are less exposed. In conclusion, the NIFT has proven to be a powerful tool to assist in the monitoring process of meteorological droughts, and it is expected that its use will be disseminated to support decision-makers in various regions of the planet.