Evaluation of WRF Model Forecasts and their Use for Hydroclimate Monitoring over Southern South America.

Abstract

Weather forecasting and monitoring systems based on regional models are becoming increasingly relevant for decision support in agriculture and water management. This work evaluates the predictive and monitoring capabilities of a system based on WRF model simulations at 15 km grid spacing over La Plata Basin (LPB) in southern South America, where agriculture and water resources are essential. The model&rsquos skill up to a lead-time of 7 days is evaluated with daily precipitation and 2m temperature in-situ observations for the 2-year period 01 August 2012 to 31 July 2014. Results show high prediction performance with 7 days lead-time throughout the domain and particularly over LPB, where about 70% of rain and no-rain days are correctly predicted. Also, the probability of detection of rain days is above 80% in humid regions. Temperature observations and forecasts are highly correlated (r>0.80) while mean absolute errors, even at the maximum lead-time, remain below 2.7°C for minimum and mean temperatures and below 3.7°C for maximum temperatures. The usefulness of WRF products for hydroclimate monitoring was tested for an unprecedented drought in southern Brazil and for a slightly above normal precipitation season in northeastern Argentina. In both cases the model products reproduce the observed precipitation conditions with consistent impacts on soil moisture, evapotranspiration and runoff. This evaluation validates the model&rsquos usefulness to forecast weather up to one week and to monitor climate conditions in real time. The scores suggest that the forecast lead-time can be extended into week two, while bias correction methods can reduce part of the systematic errors.