Thesis Defense: "Climate change and precipitation trends in the northem Mediterranean"

  • Author/PhD student: Didac Fortuny Almiñana
  • Date: 13 July 2015
  • Hour: 12:00
  • Place: Sala de Graus "Eduard Fontseré", Physics faculty
  • Tribunal:​
    • President: Dra. Yolanda Castro Díez
    • Secretary: Dra. Maria del Carme Llasat Botija
    • Vocal: Dra. Belén Rodríguez de Fonseca
    • Substitutes: Dr. Pablo Zurita Gotor, Dra.  Manuela Catalina Brunet India
  • Directors: Dra. Ileana Blade
  • Abstract: According to climate projections for the end of the twenty-first century, regional responses to global warming include a strong and widespread drying over the northern Mediterranean. Examining whether this drying signal is already detectable, we have found that only in winter and from mid-twentieth century onwards the evolution of observed precipitation series is consistent with what one would expect if a persistent signal was superimposed to internal variability. We have also determined that this winter precipitation decrease is largely explainable by an upward trend in the North Atlantic Oscillation (NAO) observed in the last decades of the twentieth century. The role played by climate change and internal variability in the observed winter northern Mediterranean and NAO trends has been examined using historical (forced) and preindustrial (unforced) CMIP5 climate simulations. Because we have found that none of these simulations contain trends as strong as the observed ones, we have considered two hypotheses: (1) the observed changes have a forced origin but the forcing (or the response to the forcing) is underestimated in climate simulations, and (2) observed changes are mainly natural but climate models underestimate the range of internal variability of northern Mediterranean precipitation. Regarding future projections of drying in the northern Mediterranean region, many studies focus on the multi-model ensemble mean without always paying attention to results for individual climate models. Evaluating inter-model consensus, however, is crucial to assess whether projections are robust or not. Aspects of the projections with good inter-model agreement are the sign of the projected northern Mediterranean area-averaged drying and its seasonal distribution. Instead, aspects with weak inter-model agreement are the magnitude of the trend, the amplitude of the decadal to multi-decadal variability and the time of emergence of the forced signal.


Monday, 6 July, 2015