Climate projections for the Guiana region

Precipitation projections over the Guiana region in northern South America are hampered by dry biases over that region in CMIP6 models. These biases are partly due to the wrong position of the inter tropical convergence zone (ITCZ) that is generally located too far to the south and unresolved mesoscale processes that are important for convective precipitation prevailing in that region. To account for that pseudo global warming (PGW) experiments with a regional climate model have been performed. In these experiments a perturbation derived from global climate models is imposed on present day simulations that are forced by reanalyses boundary conditions.  The higher spatial resolution of regional climate models allows for a better simulation of mesoscale processes and using reanalyses as boundary conditions for the present climate induces an improved position of the ITCZ. For the present climate, the RACMO regional climate model with a resolution of about 12 KM, driven by ERA5 reanalyses boundary conditions, reveals a strong reduction of the dry bias. For the future climate the PGW experiments, perturbed by an ensemble mean of CMIP6 models, indicate a strong increase in precipitation, in particular during the wet season. This contrasts with CMIP6 models that indicate a drying for that region. This has strong implications for climate adaptation measures as presently this region is already affected by large floods induced by heavy rainfall. Present research is focused on changes in extreme precipitation and on different processes explaining these differences, such the position of the ITCZ, the role of orography and the simulation of mesoscale processes.