Recommended citation: Sorí, R., Sotojanovic, M., Pérez-Alarcón, A., Ernst, J., Nieto, R., Gimeno, L. (2026). Drought variability and the role of moisture sources in North-Eastern Brazil. APARC General Assembly 2026 . Pune, India, 12-15 October 2026. https://aparc2026.tropmet.res.in/poster-presentations/210

Rogert Sorí¹, Milica Stojanovic1 , Albenis Pérez-Alarcón1 , Jakob Ernst1 , Raquel Nieto1,2 , Luis Gimeno1

Abstact

North-Eastern South America (NES) is a tropical hydroclimatic hotspot where recurrent droughts affect ecosystems, reservoirs, river discharge and the water availability required to sustain socioeconomic activities. In recent decades, parts of NES have experienced marked agricultural growth supported by irrigation infrastructure and water-management strategies. This expansion increases the importance of understanding drought variability and the atmospheric processes controlling regional moisture supply. Here we analyse monthly Standardised Precipitation Index (SPI) and the Standardised Precipitation– Evapotranspiration Index (SPEI) series at 1-, 3-, 6- and 12-month accumulation scales to characterise drought variability, persistence and trends. Drought episodes were defined as continuous negative phases reaching at least moderate intensity (≤ −0.84) and ending when positive values returned. To assess the physical role of moisture supply, we identified atmospheric moisture sources using a Lagrangian moisture-tracking framework based on FLEXPART, driven by ERA5, and analysed spatial anomalies in source contributions during contrasting dry and wet conditions. The results show a significant drying in both SPI and SPEI, with stronger trends in SPEI, indicating that evaporative demand intensifies precipitation deficit effects. SPEI trends vary from −0.19 decade⁻¹ at 1 month to −0.35 decade⁻¹ at 12 months, while SPI trends range from −0.15 to −0.29 decade⁻¹. Additionally, moisture-source diagnostics identify the tropical North and South Atlantic as the dominant oceanic sources for NES precipitation, together with regional terrestrial recycling, which is less important. During dry conditions, moisture uptake weakens over the Atlantic source regions, particularly in the western part, from 0º to 40ºS. The most persistent region associated with drought episodes was finally identified at the seasonal scale. These changes are further supported by anomalies in the vertically integrated moisture flux, confirming variations in the Atlantic moisture inflow towards NES.