Changes in mean and extreme temperature and precipitation events from different weighted multi-model ensembles over the northern half of Morocco

Saloua Balhane,Willfran Moufouma-Okia,Abdelghani Chehbouni,Omar Chafki,Fatima Driouech,Rodrigo Manzanas

doi:10.1007/s00382-021-05910-w

Abstract

Internal variability, multiple emission scenarios, and different model responses to anthropogenic forcing are ultimately behind a wide range of uncertainties that arise in climate change projections. Model weighting approaches are generally used to reduce the uncertainty related to the choice of the climate model. This study compares three multi-model combination approaches: a simple arithmetic mean and two recently developed weighting-based alternatives. One method takes into account models’ performance only and the other accounts for models’ performance and independence. The effect of these three multi-model approaches is assessed for projected changes of mean precipitation and temperature as well as four extreme indices over northern Morocco. We analyze different widely used high-resolution ensembles issued from statistical (NEXGDDP) and dynamical (Euro-CORDEX and bias-adjusted Euro-CORDEX) downscaling. For the latter, we also investigate the potential added value that bias adjustment may have over the raw dynamical simulations. Results show that model weighting can significantly reduce the spread of the future projections increasing their reliability. Nearly all model ensembles project a significant warming over the studied region (more intense inland than near the coasts), together with longer and more severe dry periods. In most cases, the different weighting methods lead to almost identical spatial patterns of climate change, indicating that the uncertainty due to the choice of multi-model combination strategy is nearly negligible.

Highlights

Morocco is one of the Mediterranean and North African countries where observed global warming impacts are the most noticeable (Lelieveld et al 2016; Sowers et al 2011; Waha et al 2017)
Based on three widely used high-resolution datasets of climate projections (Euro-CORDEX, bias-adjusted EuroCORDEX, and NEXGDDP), this study evaluates the effect of three different multi-model combination strategies on the climate changes projected over northern Morocco for the end of the twenty-first century and under two different emission scenarios (RCP4.5 and RCP8.5)
Evaluating the quality of climate models over the historical period is key to understanding the reliability of the climate change responses

Summary

Introduction

Morocco is one of the Mediterranean and North African countries where observed global warming impacts are the most noticeable (Lelieveld et al 2016; Sowers et al 2011; Waha et al 2017). Future changes in extremes are expected, including increased drought and day and night-time extreme temperature events (Betts et al 2018; Dosio and Panitz 2016; Giorgi et al 2014; Molinié et al 2018). Such changes would result in severe impacts on water resources, agriculture, and many other socio-economic sectors (Betts et al 2018; Brouziyne et al 2018; Döll et al 2018; Driouech 2010; Marchane et al 2017; Niang et al 2014; Schewe et al 2014; Tramblay et al 2016; Wanders and Wada 2015). The negative effects associated with climate change have been already witnessed in the past; i.e., drought leading to a drop in water reserves, agricultural

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