ENSO and the Spatial Extent of Interannual Precipitation Extremes in Tropical Land Areas
Journal of Climate
The extreme phases of El Niño Southern Oscillation (ENSO) are known to dominate the interannual variability of tropical rainfall. However, t he relationship between ENSO and the spatial extent of drought and excessively wet conditions is an important characteristic of tropical climate that has received relatively less atte ntion from researchers. Here, a standardized precipitation index is computed from monthly rainfall analyses and the temporal variability of the spatial extent of such
... ent of such extremes, for various levels of severity, examined from a tropics-wide perspective (land areas only, 30ºS-30ºN). Maxima in the spatial extent of both precipitation extremes are compared across multiple ENSO events which occurred during the period 1950-2003. The focus on tropical land areas is motivated by the numerous, often negative, impacts of ENSOrelated precipitation variability on human populations. Results show that major peaks in the spatial extent of drought and excessively wet conditions are generally associated with extreme phases of ENSO. A remarkably robust linear relationship is documented between the spatial extent of drought in the tropics and El Niño strength (based on Ni no 3.4 sea surface temperature anomalies), with a comparatively weaker relationship for La Niña and excessive wetness. Both conditions are found to increase by about a factor of two between strong and weak ENSO events, and in several locations they are shown to be more likely during ENSO events than at all other times, especially for severe categories. Relatively stronger El Niño events during recent decades are associated with increased drought extent in tropical land areas with increasing surface temperatures likely acting to exacerbate these dry conditions.