Thesis Defense
Student: Nilson Oliveira da Silva
Program: Meteorology
Title: “High-Resolution Climate Projections from HighResMIP for South America and the Pantanal in the Context of Moisture Transport”
Advisor: Profa. Dra. Rosmeri Porfirio da Rocha
Judging Committee:
- Profa. Dra. Rosmeri Porfírio da Rocha – IAG/USP;
- Profa. Dra. Raquel Olalla Nieto Muñiz - Universidade de Vigo (videoconferência);
- Prof. Dr. Roger Rodrigues Torres – UNIFEI (videoconferência);
- Profa. Dra. Amanda Rehbein - Pós doutoranda IAG;
- Prof. Dr. Charles Jones - University of California Santa Barbara (videoconferência).
Abstract
Understanding the sources of uncertainty that affect climate projections for South America is crucial for enhancing future climate change analysis and guiding adaptation and mitigation actions. In this context, the objectives of this study were to investigate the moisture transport to the Pantanal region, driven by low-level jets (LLJs) in the present climate (1980-2018), and the impacts of the resolution of global coupled climate models (GCMs) from the HighResMIP project on the present climate and variability (1979-2014), as well as on future climate projections of water availability for South America and the Pantanal under the SSP5-8.5 scenario (2015-2050). Moisture transport was determined through the definition of sources and sinks, applying a Lagrangian methodology, focusing on the Upper Paraguay Basin (UPB) and LLJ occurrence regions to the east of the Andes. The main moisture sources identified for the UPB are located in the Amazon Basin and the Atlantic Ocean to the north of South America during the summer months. During the remaining months, the moisture sources shift to the center-east of the continent and the South Atlantic Ocean off northeast Brazil. Although the Amazon region supplies moisture only between December and March, with peak intensity in December, it accounts for nearly 30% of the moisture received by the UPB throughout the year. LLJs were identified by considering the wind speed percentile at 850 hPa at each grid point of the domain. This enabled the selection of regions with higher intensity and frequency of LLJs, with the core LLJ regions located at the following latitudes east of the Andes: 4°N, 15°S, 19°S, and 31°S. LLJ days at 15°S favor moisture transport to the UPB, while LLJ days centered at 19°S make the UPB a moisture source for the La Plata Basin region. Five HighResMIP coupled GCM members with high (~25 km) and low (~70 km) horizontal resolution were analyzed, covering both the historical period (1979-2014) and the future period (2015-2050) under the SSP5-8.5 scenario. In the historical period, the models with higher horizontal resolution performed better in reproducing the climatology of seasonal precipitation, reducing biases and increasing spatial correlation, particularly in the tropical region. However, some challenges remain in both high and low-resolution simulations, such as reproducing the observed annual cycles of rainfall in the La Plata Basin and northeastern Brazil, and evapotranspiration in the Amazon region. Nonetheless, the higher-resolution versions generally showed smaller errors for both annual rainfall and evapotranspiration cycles, as indicated by the KGE index. Analyses of the impact of sea surface temperature variability on continental precipitation also demonstrated the superiority of higher-resolution simulations, with some models showing a 0.4 to 0.7 increase in spatial correlation between simulated and observed patterns. This increase in correlation also occurred for the observed variability pattern in the Pantanal region, but with correlations below 0.4, revealing ongoing challenges in simulating climate variability in this region. Changes in water availability for the future climate, calculated as the difference between precipitation and evapotranspiration (P-ET), showed a decreasing trend for the eastern Amazon, southeastern Brazil, and the Upper São Francisco Basin, while an increasing trend was projected for the La Plata, Upper Paraguay, and northeastern Brazil basins. Therefore, by mid-century, projections indicate that, despite a reduction in water availability for the eastern Amazon, the Pantanal region will follow the trends observed in the moisture sources located in the La Plata Basin and northeastern Brazil.
Keywords: climate change, Pantanal, CMIP6-HighResMIP, moisture transport, low level jet, surface water balance.