Abstract
<jats:p>It is currently assumed that anthropogenic climate change has differentially altered the probabilities of extreme events occurring in the development of certain meteorological phenomena, such as temperatures and precipitation, in many regions of the planet. But, there is little or no consensus on its impact on African Dust Outbreaks (ADO). The objective of this study was to estimate the contribution of global warming (thermodynamic factors) and of changes in certain atmospheric circulation types (CT, dynamic factors) to the detected increase in the development of ADO over areas of Spain (Salvador et al., 2022).To this end, values of daily probability of ADO occurrence (PROB-ADO) over eight regions of Spain in 1940-2024, were calculated with numerical prediction models (Salvador et al., 2024). ERA5 daily fields of temperature and geopotential height at different levels were used to calculate the thermodynamic parameters that feed the models and to generate daily synoptic CT maps at 850 hPa at 12 UTC. PROB-ADO extremes were thus defined as days on which PROB-ADO exceeded the 90th percentile of the time series of daily values for the period 1940-2024.Then, a circulation classification methodology was applied to group all days of this period into one of the 11 characteristic CTs identified by Salvador et al. (2022). Six out of the 11 patterns, were identified as ADO-CTs.To calculate temporal trends in the time series of annual frequencies of the 11 CTs and of values of PROB-ADO and PROB-ADO extremes over 1940-2024, the Theil-Sen methodology was used. Finally, to determine the dynamic, thermodynamic and interactive contributions of each individual CT to the general trend in the occurrence of PROB-ADO extremes, the quantitative partitioning methodology proposed by Horton et al. (2015) was applied.Statistically significant increasing trends in PROB-ADO extremes were obtained in all 8 zones for the period 1940–2024. Trend estimators ranged from 0.016 days/year in the NW zone to 0.628 days/year in the SE. There was a clear decreasing gradient along the SE-NW axis. Thermodynamic contributions were predominant, ranging from 41% in the NW to 94% in the SE sector. The dynamic contribution was smaller and varied between 9% in the SE zone and 47% in the NW. Mixed contributions were very small, ranging from -4% to 12%, and are mostly negative, indicating that this type of interaction didn’t contribute to an increase in the trend for PROB-ADO extremes. The largest overall contribution (increases of between 0.01% and 0.18% of the days in the year) came from ADO-CT1 (between 31% and 67% of the trend) and, to a lesser extent, ADO-CT6 (between 10% and 31%). Our results indicate that although a substantial portion of the observed change in PROB-ADO extremes has resulted from thermodynamic changes, it has also been altered by recent changes in the frequency of ADO-CTs.AcknowledgementsThis research received support from MITECO and from project POSAHPI-2 (ref. PID2022-143146OB-I00).ReferencesHorton, D.E. et al., 2015, https://doi.org/10.1038/nature14550.Salvador, P. et al., 2022, https://doi.org/10.1038/s41612-022-00256-4.Salvador, P. et al., 2024, https://doi.org/10.1016/j.scitotenv.2024.171307.</jats:p>