Dissertation Defense: High-frequency variability of near-surface wind speed in Northeast Brazil: current climate and future trends

This study aimed to assess high-frequency fluctuations of the near surface wind speed, through abrupt wind variations or wind ramps, and evaluate future trends in medium and long-term periods in the RCP8.5 scenario in Northeast Brazil (NEB). Data from automatic weather stations (EMAs), ERA5 reanalysis, and regional model RegCM4 simulations were used. RegCM4 climate simulations were forced by ERA-Interim and HadGEM2 and MPI global models. Initially, the spatial pattern of 100 m wind speeds in the NEB region was evaluated for the period from 1979 to 2014, dividing the region into 5 subdomains. In all selected subdomains, the highest wind velocities occur between August and October, and the lowest ones from March to May, corresponding to the dry and rainy seasons, respectively. For 8 locations in NEB, wind speed at 10 m from ERA5 and RegCM4-ERAI were evaluated, and it was found that both data tend to have higher wind speed means and medians than EMAs in various locations, but ERA5 presents higher correlation than simulation. In order to understand the high-frequency variability of wind, wind ramps (abrupt increases or decreases in speeds) were explored. It was found that wind ramps exhibit consistent behavior for nearby locations or within the same subdomain. Additionally, the influence of land-sea breezes for coastal regions and valley-mountain breezes for continental regions in defining the preferred time of onset or termination of ramps is notable. Finally, future trends of wind at 10 m were investigated with the RegCM4-HadGEM and RegCM4-MPI models for the near future period (NF - 2040-2059) and distant future period (DF - 2080-2099) compared to the reference period (RP- f 1995-2014). Both future periods indicate a consistent increase in the wind speed median, indicating a change in the frequency distribution of the data. Regarding wind ramps, coastal areas exhibited an increasing trend in the frequency of wind ramps, while for continental areas the trends are indicating wind ramps reduction for the DF.