Robustness of the Link between Precipitation in North Africa and Standard Modes of Atmospheric Variability during the Last Millennium

Arab Djebbar,François Klein,Hugues Goosse

doi:10.3390/cli8050062

Arab Djebbar, François Klein + Show 1 more

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https://doi.org/10.3390/cli8050062

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Journal: Climate	Publication Date: May 6, 2020
Citations: 8	License type: CC BY 4.0

Affiliation: Université Catholique de Louvain

Abstract

Drought is a recurring phenomenon in North Africa, and extended dry periods can have a serious impact on economic and social structures, as well as the natural environment. Consequently, understanding the mechanisms that underlie precipitation variability in the region is a key driver of sustainable economic growth in activities such as agriculture, manufacturing, energy, and transport. North Africa’s climate differs significantly between coastal and inland areas. The region has a Mediterranean climate along the coast, characterized by mild, wet winters and warm, dry summers with reasonable rainfall of around 400 to 600 mm per year. The link between winter precipitation variability in this region and atmospheric patterns is assessed here using several gridded datasets of observations and reanalysis as well as model simulations from the fifth phase of the Coupled Model Intercomparison Project (CMIP5) and the third phase of the Paleoclimate Modelling Intercomparison Project (PMIP) covering the last millennium. Results show that the link between the zonal wind index at 850 hPa (U850) and winter precipitation is stronger and more robust over time than the link with some well-known modes of variability, such as the North Atlantic Oscillation (NAO), Mediterranean Oscillation (MO), and Western Mediterranean Oscillation (WeMO). U850 better explains the interannual changes in winter precipitation variability in North Africa for the past decades as well as the last millennium. Both winter precipitation and U850 simulated time series present significant decreasing trends, associated with drier conditions, starting in the 19th century. This is in agreement with the reconstructed and simulated Palmer Drought Severity Index (PDSI), which shows a decreasing trend toward drying conditions in North Africa.

Highlights

North Africa is located in a transitional position between a wet European mid-latitude and a dry subtropical climate [1]
Results show that the link between the zonal wind index at 850 hPa (U850) and winter precipitation is stronger and more robust over time than the link with some well-known modes of variability, such as the North Atlantic Oscillation (NAO), Mediterranean Oscillation (MO), and Western Mediterranean Oscillation (WeMO)
The region is characterized by a Mediterranean climate along a thin strip of land bordering the coasts of Morocco, Algeria, Tunisia, and parts of Libya and Egypt, with mild, wet winters, warm, dry summers, and rainfall of approximately 400 to 600 mm per year (Figure 1) [2]

Summary

Introduction

North Africa is located in a transitional position between a wet European mid-latitude and a dry subtropical climate [1]. The region is characterized by a Mediterranean climate along a thin strip of land bordering the coasts of Morocco, Algeria, Tunisia, and parts of Libya and Egypt, with mild, wet winters, warm, dry summers, and rainfall of approximately 400 to 600 mm per year (Figure 1) [2]. North African countries have semi-arid and arid desert climates that regularly display extreme conditions with very hot summers, cold winters, and little rainfall, between 200 and 400 mm per year or even less in some regions [2]. The precipitation occurs mostly during the winter season (November to April) [1]. Climate 2020, 8, 62; doi:10.3390/cli8050062 www.mdpi.com/journal/climate Atl s ta un Mo in

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