Llasat et al. (2021) Convective precipitation trends in the Spanish Mediterranean region

Identification

• Journal: Atmospheric Research
• Year: 2021
• Date: 2021-03-18
• Authors: María Carmen Llasat, Anna del Moral, María Cortès, Tomeu Rigo
• DOI: 10.1016/j.atmosres.2021.105581

Research Groups

• GAMA, Department of Applied Physics, University of Barcelona, Barcelona, Spain
• Meteorological Service of Catalonia, Barcelona, Spain
• AEMET, Barcelona, Spain

Short Summary

This paper analyzes the distribution and temporal evolution of convective precipitation in the Spanish Mediterranean region using 5-minute rainfall data. It reveals a significant increase in convective precipitation, particularly in the Júcar Hydrographic Confederation, often concentrated in fewer, more intense events, which aligns with climate change impacts on atmospheric instability despite varying trends in total annual precipitation.

Objective

• To analyze the distribution and temporal evolution of convective precipitation in the Mediterranean region of Spain, specifically in the Júcar Hydrographic Confederation (CHJ) and the Internal Basins of Catalonia (CIC), and to identify any potential trends in convective precipitation or different types of convective events over an extended period.

Study Configuration

• Spatial Scale: Two hydrographic basins in the Mediterranean region of Spain: the Internal Basins of Catalonia (CIC, approximately 16,000 km²) and the Júcar Hydrographic Confederation (CHJ, 22,261 km²).
• Temporal Scale: Data from 1989–2015 (CHJ) and 1996–2015 (CIC), with a total of 129 stations analyzed.

Methodology and Data

• Models used:
  • K-means clustering (R package, Hartigan and Wong, 1979) for rainfall regionalization.
  • Mann-Kendal non-parametric test (R-package, Rai et al., 2013) for trend analysis.
  • Quantum GIS (Essen 2.14 version) for including topographic factors in regionalization.
• Data sources:
  • 148 sets of 5-minute rainfall rate data from automatic rain gauges (129 stations after quality control).
  • Data from the SAIH (Automatic Hydrological Information System) network belonging to the Catalan Water Agency (for CIC) and the Júcar Hydrographic Confederation (for CHJ).
  • Convective precipitation defined by a 5-minute rainfall intensity threshold of 35 mm/h.
  • Convective events categorized as "very convective" (β ≥ 80%), "moderately convective" (80% > β ≥ 30%), and "slightly convective" (30% > β > 0), where β is the ratio of convective precipitation to total precipitation.

Main Results

• Convective precipitation contributes, on average, between 10% and 16% of total annual precipitation, but is generated by a very small percentage (3% to 6%) of total rainfall episodes.
• Moderately convective events are the most common, with a predominantly unimodal monthly distribution of β, indicating summer (July-September) as the most convective season.
• In the Júcar Hydrographic Confederation (CHJ), significant positive trends were observed for total precipitation, convective precipitation (annual β increase up to 5% per decade), and the number of convective days and episodes (up to 20 days/century and 20 episodes/century, respectively).
• In the Internal Basins of Catalonia (CIC), a positive trend in convective precipitation contribution (annual β) was found despite an overall decrease in total annual precipitation, suggesting an increase in the torrentiality of events (precipitation concentrated in fewer events), particularly in summer.
• The CHJ exhibits greater torrentiality than the CIC, with some months showing 100% convective precipitation and a higher relative and absolute number of "very convective" events (exceeding 10% across all clusters, reaching 34% in some, compared to less than 20% in the CIC).
• Orography (height and orientation) and Sea Surface Temperature (SST) play crucial roles in the spatial structure and intensity of convective precipitation.

Contributions

• Provides a comprehensive characterization and trend analysis of convective precipitation in a large area of the Spanish Mediterranean using high-resolution (5-minute) rainfall data.
• Highlights that the increase in convective precipitation, often concentrated in fewer events, is a significant impact of climate change that may not be detected by analyzing only daily precipitation extremes.
• Emphasizes the critical need to work with sub-daily precipitation series to accurately assess climate change impacts on heavy rainfall and flash floods in the Mediterranean region.
• Offers insights into the regional differences in convective precipitation patterns and trends, linking them to local geographical and meteorological factors.

Funding

• M-CostAdapt research project (CTM2017-83655-C2-2-R), funded by the Spanish Ministry of Economy and Competitiveness (MINECO/AEI/FEDER, UE).
• PIRAGUA project EFA210/16, funded by INTERREG/POCTEFA.

Citation

@article{Llasat2021Convective,
  author = {Llasat, María Carmen and Moral, Anna del and Cortès, María and Rigo, Tomeu},
  title = {Convective precipitation trends in the Spanish Mediterranean region},
  journal = {Atmospheric Research},
  year = {2021},
  doi = {10.1016/j.atmosres.2021.105581},
  url = {https://doi.org/10.1016/j.atmosres.2021.105581}
}