The Impact of Climate Change on Changes in the Duration of Shallow and Deep Trough and Ridge Patterns over Iraq during the Rainy Season

Abstract

This study aims to examine the impact of climate change on the patterns of occurrence of atmospheric troughs and ridges over Iraq during the rainy season. Three minor climatic cycles were identified, each extending over eleven rainy seasons: 1954–1964, 1984–1994, and 2014–2024. The number of days of persistence for the four patterns of troughs and ridges, in both their deep and shallow forms, was determined. The results revealed a trend toward a decline in the number of days associated with the persistence of deep polar trough patterns, accompanied by an increase in their shallow cases, while both the deep and shallow cases of tropical ridges showed an increase over Iraq.

The weakening of deep polar trough activity during Iraq’s rainy season reduces the activity of surface depressions, transforming them into shallow, short-lived systems, and weakens atmospheric instability associated with the activity of the accompanying air fronts. This, in turn, affects rainfall amounts, which have been declining in recent years. In contrast, the growing dominance of tropical ridges and the lengthening of their duration of persistence result from the displacement of the Hadley Cell toward the middle latitudes during the rainy season, which increases the occurrence of atmospheric stability and activates surface high-pressure systems that function as pressure barriers, preventing the advance of depressions and contributing to the predominance of drought conditions.