Modeling the impacts of La Ni&#241;a's reduced solar radiation on the functioning of a central Amazon forest
Authors: Rocha Cardeli Bárbara , Fazio Rius Bianca , Darela Filho João Paulo , Montenegro Lapola David 
Published: February 2023

&lt;p&gt;Studies show that global warming resulting from the increase of greenhouse gases (GHG) in the atmosphere has impacted the planet&#039;s climate patterns and intensified the El Ni&amp;#241;o-Southern Oscillation (ENSO), an atmospheric-oceanic phenomenon that groups the events known as El Ni&amp;#241;o and La Ni&amp;#241;a, for example. La Ni&amp;#241;a events are occurring with a higher frequency than expected and bringing significant consequences for different regions of the planet. In northern South America, as in the Brazilian Amazon, La Ni&amp;#241;a is responsible for intensifying rainfall, which also increases cloudiness in the region and reduces light radiation. Such a condition can impact the ecophysiological processes of the Amazon rainforest and force a functional restructuring of the community via light competition. Thus, the main objective of this study is to evaluate how the decrease in light radiation associated with more frequent La Ni&amp;#241;a events can impact the functional composition in a central Amazonian forest plot, as well as ecosystem flows and stocks, such as net primary productivity (NPP) and aboveground biomass. For this, we will use modeling as our primary tool. We will carry out simulations with gradual decreases in Photosynthetically Active Radiation (PAR) observed in La Ni&amp;#241;a years through a trait-based dynamic global vegetation model called CAET&amp;#202; (&lt;strong&gt;CA&lt;/strong&gt;rbon and &lt;strong&gt;E&lt;/strong&gt;cosystem functional &lt;strong&gt;T&lt;/strong&gt;rait &lt;strong&gt;E&lt;/strong&gt;valuation model). CAET&amp;#202; model represents the light competition through the difference of luminous incidence (PAR) in vertical vegetation strata. As preliminary results, we expect to observe a decrease in the photosynthetic rate that will also result in a decrease in NPP in the lower strata of the forest and a functional reorganization to favor and select plant strategies with higher stature and with greater efficiency in capturing light. Therefore, it is expected higher plants individuals will have a better performance in the light competitive dynamics and survival than those individuals that will be in lower strata and will have their photosynthetic rate, as well as their productivity and survival, affected by the low availability of radiation and the competitive effect. In the same way, it is expected to observe changes in the distribution of key traits such as wood density, specific leaf area (SLA), and leaf area index (LAI), which have an intrinsic relationship with height, competitive effect, and light resource capture, respectively, and impact on other important processes such as mortality and growth, also altering the ecosystem&#039;s biomass stock. Our analyzes will also include simulations with increased CO&lt;sub&gt;2&lt;/sub&gt; (600 ppmv), according to the experiments on AmazonFACE. It is expected that our results and approaches will help investigate how changes in climate patterns and the increase in the frequency of extreme climate events, such as La Ni&amp;#241;a, impact ecophysiological processes and functional and ecosystem dynamics of the largest tropical forest in the world. Final results will be obtained until the EGU congress takes place.&lt;/p&gt;