WRF convective gray-zone simulations of the freshwater flux over the Ca Mau Peninsula, Southern Vietnam: Impacts of planetary boundary layer parameterizations

Freshwater flux over the Ca Mau Peninsula, Southern Vietnam, is crucial for sustaining regional food production, ecosystem functioning, and the livelihoods of communities that rely on agriculture and aquaculture. This study examines the sensitivity of two components of the freshwater flux, namely, simulated precipitation and potential evapotranspiration (PET), to planetary boundary layer (PBL) schemes and diurnal sea surface temperature (SST) variability using the Weather Research and Forecasting (WRF) model over the Ca Mau Peninsula. Convective gray-zone (5 km) simulations were conducted for three representative years corresponding to El Niño, ENSO (El Niño – Southern Oscillation) neutral, and La Niña conditions, using ERA5 boundary conditions. Three PBL schemes (Mellor–Yamada–Nakanishi–Niino Level 2.5: MYNN2.5, Mellor–Yamada–Janjic: MYJ and Asymmetric Convection Model 2: ACM2) were tested with or without the activation of the SST skin temperature option. Simulated precipitation was evaluated against rain gauge observations and satellite-based datasets, while PET was assessed using station-based estimates derived from the Penman–Monteith method and ERA5 reanalysis data. ... mehrThe results indicate that MYNN2.5 and MYJ reproduce observed rainfall patterns more accurately than ACM2, which exhibits a pronounced wet bias. Incorporating diurnal SST variability reduces precipitation biases by 10–40%. All schemes capture the general features of the diurnal rainfall cycle, although nighttime rainfall is systematically underestimated; among them, MYNN2.5 most accurately represents both inland and coastal rainfall peaks. PET simulations are also sensitive to the choice of PBL scheme, with MYNN2.5 showing the lowest overall bias. Overall, the MYNN2.5 scheme combined with the diurnal SST option provides the most reliable representation of the freshwater flux over the Ca Mau Peninsula. These findings offer important insights for improving freshwater flux simulations over the Ca Mau Peninsula, the most important aquaculture hub in Vietnam.