On Climate Prediction in the Tropics.

Climatic disasters are common in many tropical regions, and rainfall anomalies in particular have a severe human impact. Accordingly, both the World Climate Programme and the U.S. National Climate Program have identified climate prediction as a major objective. Approaches can be grouped into five major categories: (i) the extrapolation of empirically or theoretically deduced periodicities; (ii) the assessment of statistical relationships between rainfall and various meteorological elements; (iii) the relation between rainfall in the preseason and at the height of the rainy season; (iv) comprehensive diagnostic studies of climate and circulation anomalies combined with statistical methods; and (v) numerical modeling.Methods pertaining to (iv) indicate the feasibility of empirically based climate prediction for certain tropical regions. For the drought-prone region of northeast Brazil and Indonesia, in particular, it has been demonstrated on independent data sets that almost half of the interannual rainfall variability can be explained from antecedent departures in the large-scale circulation. Application of these methods on an operational basis involves two simultaneous input data requirements: 1)they must be available in quasi real time; 2) long (>10 years) homogeneous reference series of internally consistent parameters are needed, while absolute calibration is not essential. The practical benefit of climate forecasts appears to hinge on societal and economic factors.