Long-term precipitation in the Maghreb reveals significant changes in timing and intensity

This study analyzes trends in timing, intensity, and geographical influences on rainfall using long-term datasets. Findings reveal increased droughts, delayed rainy seasons, and intensified spring precipitation, emphasizing regional resilience needs.
Published in Earth & Environment and Statistics
Long-term precipitation in the Maghreb reveals significant changes in timing and intensity
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Statistical analysis of long-term precipitation in the Maghreb reveals significant changes in timing and intensity - Theoretical and Applied Climatology

The Mediterranean is commonly recognized as a climate change hotspot where the rate of warming is greater than global and disturbances in precipitation patterns are predicted. Despite this, knowledge gaps are still identified in the South with respect to the lack of regional projections and studies of key elements such as trends, concentration, disparity, deviation, and their association with regional geographical factors. Here, these gaps were addressed in the Maghreb using appropriate statistical methods (Mann–Kendall test, consecutive disparity, daily concentration, Spearman correlation, and categorization of precipitation) based on long-term daily datasets from 45 scattered meteorological stations. It was found that precipitation is channeled under the orographic effect of the Atlas and Rif Mountain belts and the latitudinal gradient (continentality), which spatially determine the abundance of precipitation and the duration of dry periods along a dominant North–South axis. The two factors combine with maritime effects (Mediterranean and Atlantic) to favor the north of the mountain belts with high daily concentrations, low interannual disparity but negative trend, and frequent disturbances. An intra-annual time shift was found in the number of days of significant precipitation (≥ 10 mm) of 2 to 7 fortnights with respect to the core of the rainy season (December–January) with a decrease in precipitation intensity in winter and an increase in spring and summer. The result is a forecasted precipitation deficit marked by more widespread and intense droughts, and more intense but delayed and spatiotemporally dispersed precipitation according to a disturbed and non-sequential character in places of abundance (North, East, and West of the Mountain belts). Overall, the projected precipitation pattern is likely to entrain prolonged and staggered intra-annual droughts (even in wet years) with deep ecological and socio-economic impacts, and repetitive hydroclimatic hazards, making it necessary to improve collaborative resilience measures to cope with hydro-agricultural needs.

Recent droughts and flash floods are two sides of the same coin, both driven by the shifting precipitation patterns in the Mediterranean, a  Climate Change hotspot.

The Maghreb faces shifting precipitation patterns with significant ecological and socio-economic implications. This study analyzes trends in timing, intensity, and geographic factors using datasets spanning over 50 years. Results indicate that the Atlas and Rif Mountain belts shape precipitation distribution, favoring the northern regions with higher rainfall. However, negative trends signal a growing deficit, with droughts becoming more intense and widespread. Key findings include delayed rainy seasons by up to 7 fortnights, reduced winter precipitation (19%), and increased spring and summer rainfall (8.7% and 9%, respectively), contributing to flash floods and water shortages. The daily precipitation concentration index highlights disparities, with intense, sporadic downpours outside traditional rainy seasons. This disturbed pattern poses challenges for agriculture, infrastructure, and water management. Recommendations emphasize collaborative resilience strategies, leveraging these insights to mitigate risks and adapt to evolving hydroclimatic hazards.

Embarking on our research journey, my colleague, Professor Javier Martín-Vide, a distinguished climatologist from the University of Barcelona (where ten years earlier I had completed my PhD), and I identified a significant gap in climate data for the southern Mediterranean. This region, despite being highly vulnerable to climate change, lacked comprehensive and accessible meteorological records, posing a challenge for accurate climate analysis. While northern Mediterranean countries benefit from abundant climate studies, the southern side had long been overlooked, leaving critical questions unanswered about the impacts of shifting precipitation patterns.

Determined to bridge this gap, we initiated an extensive data collection effort. The process was arduous, involving collaboration with various national meteorological services, navigating bureaucratic hurdles, and often dealing with fragmented or non-digitized records. Some datasets required months of negotiations to access, while others had to be manually digitized from paper records. Over three years, we painstakingly gathered and validated historical climate data from 45 meteorological stations, ensuring its accuracy and reliability for our study. This comprehensive dataset provided a foundation for robust analysis, giving unprecedented insights into precipitation trends across the region.

Concurrently, we engaged in in-depth discussions to select appropriate statistical methods for analyzing the data. The region's climate patterns are shaped by complex interactions between the Mediterranean, Atlantic, and desert systems, as well as the influence of the Atlas and Rif Mountain ranges. These interactions required a multifaceted approach to capture subtle trends and variations. Our deliberations led us to adopt advanced metrics, such as the Consecutive Disparity Index (D) and Daily Concentration Index (CI). These tools allowed us to assess not just annual precipitation totals, but also the intensity, timing, and spatial distribution of rainfall events. This methodological framework enabled us to identify critical contrasts between northern wet zones and southern arid areas, as well as the shifting dynamics of rainy and dry seasons.

The results of this study reveal several alarming trends. The rainy season, which traditionally spans December to February, has shifted by up to seven fortnights, with significant precipitation now occurring later in the year. Winter precipitation has declined sharply, while spring and summer rains have intensified, increasing the risk of flash floods. These trends have profound implications for water resource management, agriculture, and disaster preparedness. For example, the concentration of rainfall into shorter periods places greater strain on water storage infrastructure, while prolonged dry spells exacerbate drought conditions.

Beyond scientific insights, this collaborative effort contributed to the broader scientific community by enhancing climate data availability for the southern Mediterranean—a region previously underrepresented in climate studies. By consolidating fragmented datasets and employing innovative methodologies, we hope our work will serve as a benchmark for future research and policymaking. The findings underscore the urgency of designing adaptive strategies to mitigate the impacts of climate change and build resilience in vulnerable regions. Moreover, they highlight the value of international collaboration in addressing shared challenges, particularly in data-scarce regions where resources and expertise must be pooled for maximum impact.

Reflecting on the journey, this project was not just an intellectual challenge but also a logistical one, demanding persistence, creativity, and collaboration. Working alongside Professor Martín-Vide, whose expertise and guidance were invaluable, I am reminded of the power of partnerships in science. Together, we not only bridged a critical knowledge gap but also laid the groundwork for a deeper understanding of the Mediterranean's evolving climate, a mission that continues to drive us forward.

Building on this foundation, further work is currently underway to deepen our understanding of the environmental and climate evolving patterns in the southern Mediterranean. Ongoing research focuses on integrating more extensive datasets, analyzing teleconnections, and refining predictive models to better assess the complex interactions shaping this vulnerable region. By exploring the drivers behind these changes and their socio-ecological consequences, we aim to provide actionable insights that will empower policymakers and communities to adapt to and mitigate the challenges posed by a rapidly changing climate.

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