Evaluation of Precipitation Simulations at the Subseasonal Range in the Sao Francisco River Basin, Brazil

The objective of this work is to evaluate the subseasonal precipitation simulations of the Eta model during the onset of the rainy season in the Sao Francisco River Basin (SFB). Accumulated precipitation every 20 days in September and October (2011 to 2015) was evaluated based on subseasonal simulations (integration period of up to 60 days) of the Eta-20- km model, nested within the Climate Forecast System Reanalysis (CFSR), here called Eta-CFSR. MERGE precipitation data were used to evaluate Eta- CFSR simulated precipitation. A statistical method was employed to evaluate the model’s ability to simulate the onset of the rainy season in the Upper SFB. The main results are: i) The Eta-CFSR accurately represents the seasonality of the precipitation pattern in the SFB and the seasonal and interannual variation of the accumulated precipitation in all of the chosen three consecutive 20-day periods of years 2011 to 2015; ii) The model can represent the transition pattern from the dry to the rainy season, showing better results in 2011 and 2015, which were marked, respectively, by La Niña and El Niño, and by anomalies of sea surface temperature favorable and unfavorable for the occurrence of precipitation; iii) Although the model underestimates the amount of precipitation, it effectively captures the seasonal patterns and the onset of the rainy season, with a maximum advancement of two pentads in wetter years and delaying it in drier years.