Simulating Multi-Season Past Droughts
Abstract

Abstract Author: Bradfield Lyon

Abstract Title: The Joint Occurence of Summer Drought and Heat Waves in Coupled Models

Abstract: Drought during warm seasons is often, though not always, accompanied by elevated surface air temperatures and even heat waves, the linkage between these phenomena being variations in the surface energy balance. While there is near-unanimity among climate model projections that surface air temperatures will increase (favoring heat waves), projected changes in precipitation are less clear (particularly on the regional scale) making it unclear what the joint behavior of heat waves and drought might be in the future.

An investigation was therefore undertaken to examine the joint occurrence of drought and heat waves in coupled models and in observations, with the the focus primarily on the southern Africa subcontinent. Joint probability distributions of drought (based on various drought indices) and daily maximum temperature measures were generated to 1) compare observations with coupled model output for the last four decades of the twentieth century and 2) examine this joint behavior in model projections for the first half of the twenty-first century. Spatial variations in the occurrence of drought and heat waves was also considered in both observations and coupled models. General characteristics of the anomalous atmospheric circulation associated with heat waves in different parts of southern Africa are presented as well as the relationship between heat waves and drought during El Nino events. The influence of increased atmospheric demand for water on drought is also evaluated in climate projections for the twenty-first century.

This work was funded by the NSF under the DRICOMP initiative.