The gross primary production (GPP) of an ecosystem, that is, the carbon it assimilates via photosynthesis, differs strongly from one year to the next. This variability between years is called the interannual variability (IAV) of GPP and the reasons for why GPP can change substantially from year to year are unclear. From a global scale analysis, we know that the seasonal cycles in precipitation and temperature in semi-arid ecoystems contribute substantially to the global IAV of GPP, highlighting the role of water and heat. We also know that even a few unusual hours in a total year can contribute disproportionately more to an ecosystems annual carbon uptake. For example, just 2% of unusually hot hours can account for ca. 10% of an ecosystems’ total annual GPP. Considering an increase in frequency and intensity of extreme events under climate change, a better quantification and characterisation of GPP extremes is crucial to estimate the future global carbon balance.
The goal of this project is to quantify the role of GPP extremes on an ecosystem’s carbon uptake, using FLUXNET data (half-hourly measured land-atmosphere exchange of carbon dioxide). The first aim is to identify years that show GPP extremes, that is, anomalies in their annual total GPP. Then, a suitable method to assess the effect of extreme days within these anomalous years on the year’s total GPP is explored by (e.g., using a Gini index). Further questions may cover investigating the difference across globally distributed sites or comparing observed against modelled GPP to identify the drivers of GPP extremes.