Effects of El Nino on Panama rainfall.

Abstract

The effect of El Nino on the rainfall in Panama has been studied. Thirteen episodes of El Nino during the period, 1920 to 1983, were analyzed. The results show that El Nino produces below normal rainfall in almost all regions of Panama. The average annual rainfall anomaly, based on all occurrences of El Nino, is 8% below normal. In the case of the strong El Nino episodes of 1976 and 1982, the corresponding anomalies are 28% and 24% below normal, respectively. The driest month of the year 1982 (December) has a rainfall anomaly of about 60% below normal. The results of the study also showed that there is a considerable geographical variation in the rainfall anomalies. In the case of the El Nino of 1976, the largest magnitudes of the negative anomalies are located in the SW part of Panama, just S of the central cordillera on the Pacific side. On the other hand, El Nino had the opposite effect (positive anomalies) N of the cordillera in the Atlantic coastal region. The relationship between the time variations of the annual rainfall anomalies and sea surface temperature anomalies in the E Pacific was studied. A high negative correlation was found between the rainfall anomalies and the sea surface temperature anomalies during the preceding months. This high correlation has been used to devise a method for long range forecasting of rainfall. -Authors