Flash Drought and Its Characteristics in Northeastern South America during 2004–2022 Using Satellite-Based Products

Abstract

The term flash drought describes a special category of drought with rapid onset and strong intensity over the course of days or weeks. To characterize the impact of flash droughts on vegetation coverage, this study assessed the influence of soil water deficits on vegetation dynamics in the northeastern South America region by combining time series of vegetation index, rainfall, and soil moisture based on satellite products at a daily time scale. An 18-year analysis, from 2004 to 2022, of the Normalized Difference Vegetation Index (NDVI), Standard Precipitation Index (SPI), and surface soil moisture (SSM) was performed based on three different satellite remote sensing estimates: the spinning enhanced visible and infrared imager (SEVIRI) and the integrated multi-satellite retrievals algorithm (IMERG), and the soil moisture and ocean salinity (SMOS). The results revealed that flash drought events exerted dramatic impacts on terrestrial ecosystems in the study region during the first two decades of the 2000s, with changes in seasonal and regional vegetation dynamics. Further, the fixed-threshold values to characterize flash drought events were suggested as the timing when the water deficit was less than −1.0 units and vegetation index reached the value equal to +0.3 during five consecutive weeks or more, coupled with soil moisture rates below 40% percentile, leading to a strong region-wide drought throughout the entire region. Additionally, the results of linear least squares trend analyses revealed a negative trend in the pentad-SEVIRI radiance for the solar channel 1 within the semiarid ecosystems of the study region (i.e., the Caatinga biome) that was suggested as a reduction in clouds in the 18 years of the study. Developing combined threshold measures of flash drought based on satellite remote sensing may lead to an accurate assessment of flash drought mitigation.

Geospatial Insights into Aridity Conditions: MODIS Products and GIS Modeling in Northeast Brazil

“…More recently, a study detected arid conditions in these regions of NEB. Barbosa [13] studied drought and its characteristics over several days in Northeast South America using satellite data from 2004 to 2022, discovering that drought and rainy cycles had considerable impacts on the vegetation dynamics, with a trend of increasing temperatures mainly in the central region of NEB due to the high level of land degradation, presenting in these regions the occurrence of arid areas, i.e., areas where the vegetation no longer responds to the climatic factors. Feng and Fu [1] analyzed the expansion of global drylands based on climate model simulations from 1948 to 2100 and highlighted that there will be a greater expansion of semiarid and arid lands on the continents, which will consequently increase the population affected by water scarcity and soil degradation.…”

“…At a global level, the intensification of extreme climate change events mainly affects rainfall rates, driving severe droughts. In addition, the impacts caused by human activities also accelerate and lead to significant changes [3][4][5][6], with emphasis for semiarid areas of Brazil, such as the Northeast Region (NEB) and Brazilian Semiarid Region, where studies on the detection of vulnerabilities related to environmental degradation processes and soil desertification, based on radiation and energy balance components, help to understand the dynamics of these factors over time [7][8][9][10][11][12][13][14][15][16].…”

“…Specifically, for regions of NEB, besides being historical, droughts have been frequent, providing extreme and highly dynamic climatic and hydrological conditions [13,14,[30][31][32][33][34]. It is noteworthy that NEB and its sub-regions are associated with various large-scale and complex climatic phenomena, characterized by a set of meteorological phenomena and climatological conditions that cause instability in rainfall [9,[35][36][37][38][39][40][41][42][43].…”