# Predominantly positive XCO2 anomalies in the Caatinga biome highlight carbon vulnerability

## TL;DR

The Caatinga biome in Brazil shows mixed carbon balance patterns, with some areas acting as carbon sinks and others as emission hotspots, influenced by climate and land use.

## Contribution

This study identifies localized carbon emission hotspots and varying carbon sink strengths in the Caatinga biome using satellite CO2 data and spatial analysis.

## Key findings

- The Caatinga biome is mostly a carbon sink but has localized emission hotspots in the Savanna-Steppe and Pioneer Formation biozones.
- Forested biozones show increasing CO2 anomalies, suggesting weakening carbon sink capacity in recent years.
- Carbon fluxes in the Caatinga are strongly influenced by precipitation and vegetation indices, highlighting hydrological control.

## Abstract

The Caatinga biome, the only exclusively Brazilian biome, plays a crucial yet understudied role in regional and global carbon dynamics. Using column-averaged dry-air mole fraction of CO2 (XCO2) data from NASA’s Orbiting Carbon Observatory-2 (OCO-2) between 2015 and 2022, this study investigates spatial and temporal anomalies across distinct phytoecological biozones of the Caatinga. Anomaly detection, spatial autocorrelation (Local Moran’s I), time-series modeling (ARIMA), and correlation analyses with vegetation and climate indices (NDVI, EVI, LAI, land surface temperature, and precipitation) were applied to evaluate the biome’s carbon balance. Results reveal heterogeneous XCO2 patterns, with predominantly negative or neutral anomalies, confirming the Caatinga’s role as a carbon sink, though punctuated by localized positive anomalies indicating emission hotspots. The Savanna-Steppe and Pioneer Formation biozones exhibited the strongest seasonal and spatial clustering of positive anomalies, highlighting vulnerability to land-use pressures and climatic extremes. Forested biozones, particularly Open and Dense Ombrophilous Forests, showed increasing anomaly trends in recent years, suggesting a potential weakening of sink capacity. Correlations revealed distinct biome-specific responses: positive associations between XCO2 and precipitation in transitional and pioneer formations, and negative associations with vegetation indices in savanna areas, emphasizing hydrological control of carbon fluxes. The findings demonstrate that the Caatinga exhibits both resilience and vulnerability, with its carbon balance strongly modulated by climatic variability, vegetation structure, and anthropogenic pressures. These results underscore the biome’s strategic role in climate mitigation and the urgent need for targeted conservation and restoration policies to safeguard its carbon sequestration potential.