Spatiotemporal Variability of CO2, Solar-Induced Fluorescence, And Precipitation Over the Tropical Rainforests

Tropical rainforest ecosystems change forest dynamics during the dry/fire season, transitioning from an atmospheric CO2 sink to a CO2 source. The Amazon basin, Congo basin, and the tropical Indo-Pacific play vital roles in biospheric processes, which contribute to Earth’s atmospheric CO2 concentration. This investigation will use various space-based and ground-based datasets and empirical models to explore photosynthetic activity, spatiotemporal variability, and correlation among critical variables (e.g., Solar-induced chlorophyll fluorescence (SIF), CO2, precipitation, high vapor pressure deficit (VPD), and burned areas). Specifically, we use Orbiting Carbon Observatory 2 (OCO-2) SIF, OCO-2 CO2, Global Precipitation Climatology Project (GPCP) precipitation, Moderate Resolution Imaging Spectrometer (MODIS) burned area, and CarbonTracker Model. Over the entire Amazon basin from September 2014 to December 2019, we found a positive temporal correlation (0.94) between OCO-2 SIF and GPCP precipitation and a negative temporal correlation (–0.64) between OCO-2 SIF and OCO-2 CO2. These findings suggest that precipitation enhances photosynthesis, thus resulting in higher values for SIF and the rate of removal of atmospheric CO2 in the Amazon region. We also identify seasonal variations in the spatial distributions of these variables across the Amazon region. Over the Congo basin, during the same timeframe (Sep 2014-Dec 2019), we find that the atmospheric CO2 is ~2 ppm higher than the regional background during the boreal summer (June–August), primarily due to biomass burning and significantly reduced photosynthetic activities during the dry season. Over the tropical Indo-Pacific, we explore the spatial distributions of SIF, CO2, and precipitation during El Niño events verse other months. The CarbonTracker Model is employed to assess the impact of El Niño on atmospheric CO2. Various datasets of deseasonalized precipitation, deseasonalized SIF, and deseasonalized CO2 are analyzed in time series averaged over 10S-10N, 100E-160E. We have discovered that there is less precipitation, more sinking air, lower SIF, and higher CO2 over the Indo-Pacific region during the El Niño events. The CarbonTracker model can simulate the increase of atmospheric column CO2 during the El Niño event, although there are some difficulties in capturing the correct spatial distribution of CO2 anomalies. These findings suggest that improved seasonal fire management practices in these tropical regions are critical components needed to achieve successful and timely reductions in global carbon emissions, as set forth by international agreements.