Droughts, floods, and sea‐surface temperature anomalies: A modelling approach

As the first phase of a research programme to develop a deterministic drought prediction scheme a general circulation model has been used to simulate rainfall perturbations forced by sea-surface temperature anomalies in the Pacific Ocean. A wavenumber 21 model with four vertical levels run in a fixed January mode, but with diurnal variability, was used. Three different sea-surface temperature anomaly patterns were explored, representative of both El Nino and anti-El-Nino events. Compared with a control run, global perturbations in rainfall and soil moisture were produced, but for simplicity, analysis was restricted primarily to the overall Pacific region where the model response was highest. For El Nino type temperature anomalies large-scale droughts were produced in eastern Australia and Venezuela, while enhanced rainfall conditions prevailed in the central Pacific and Peru. An analysis is presented that clarifies some of the mechanisms involved in creating these rainfall perturbations. Diurnal variations of conditions at individual model grid points highlight the differences occurring for control and drought situations, and illustrate the ability of the model to provide a range of climatic outputs that assist in the assessment of the impact of a drought. Time-series plots of condensational heating in the model troposphere show that there is not a simple relationship between imposed SST anomalies and the consequent release of latent heat in the atmosphere.