3 nous artícles

On the key role of droughts in the dynamics of summer fires in Mediterranean Europe

 

Marco Turco, Jost von Hardenberg, Amir AghaKouchak, Maria Carmen Llasat, Antonello Provenzale, Ricardo M. Trigo

 

Summer fires frequently rage across Mediterranean Europe, often intensified by high temperatures and droughts. According to the state-of-the-art regional fire risk projections, in forthcoming decades climate effects are expected to become stronger and possibly overcome fire prevention efforts. However, significant uncertainties exist and the direct effect of climate change in regulating fuel moisture (e.g. warmer conditions increasing fuel dryness) could be counterbalanced by the indirect effects on fuel structure (e.g. warmer conditions limiting fuel amount), affecting the transition between climate-driven and fuel-limited fire regimes as temperatures increase. Here we analyse and model the impact of coincident drought and antecedent wet conditions (proxy for the climatic factor influencing total fuel and fine fuel structure) on the summer Burned Area (BA) across all eco-regions in Mediterranean Europe. This approach allows BA to be linked to the key drivers of fire in the region. We show a statistically significant relationship between fire and same-summer droughts in most regions, while antecedent climate conditions play a relatively minor role, except in few specific eco-regions. The presented models for individual eco-regions provide insights on the impacts of climate variability on BA, and appear to be promising for developing a seasonal forecast system supporting fire management strategies.

Article: http://www.nature.com/articles/s41598-017-00116-9

Analysis of geographic and orographic influence in Spanish monthly precipitation

J. Álvarez-Rodríguez, M. C. Llasat, T. Estrela

Precipitation is a major concern in water resources studies. Being a main variable, the inefficiency of historical ground network, particularly at higher altitudes where precipitation and runoff augmentations are expected, constitutes a major drawback. This work analyses the competence of Spanish historical precipitation network and explores the physiographic influence of elevation and orientation at a national scale. The usefulness of slopes is also explored. Nearly 12 000 monthly precipitation series recorded from the 19th century until the hydrological year 2004/2005 over a high-resolution topographic map (200 m) of Spanish territory are used. Comparable statistics and precipitation lapse rates are managed once a completion of gaps is accomplished. Then, Spanish yearly rates range from 0.3 to 1.2 mm m−1, reaching 1.5 mm m−1 in Northern Iberian Peninsula, diminishing at highest altitudes.

Article: http://onlinelibrary.wiley.com/doi/10.1002/joc.5007/full

Bias correction and downscaling of future RCM precipitation projections using a MOS-Analog technique

M. Turco, M.C. Llasat, S. Herrera, J.M Gutiérrez

In this study we assess the suitability of a recently introduced analog-based Model Output Statistics (MOS) downscaling method (referred to as MOS-Analog) for climate change studies and compare the results with a quantile mapping bias correction method. To this aim, we focus on Spain and consider daily precipitation output from an ensemble of Regional Climate Models provided by the ENSEMBLES project. The reanalysis-driven Regional Climate Model (RCM) data provide the historical data (with day-to-day correspondence with observations induced by the forcing boundary conditions) to conduct the analog search of the control (20C3M) and future (A1B) global climate model (GCM)-driven RCM values. First, we show that the MOS-Analog method outperforms the raw RCM output in the control 20C3M scenario (period 1971–2000) for all considered regions and precipitation indices, although for the worst-performing models the method is less effective. Second, we show that the MOS-Analog method broadly preserves the original RCM climate change signal for different future periods (2011–2040, 2041–2070, 2071–2100), except for those indices related to extreme precipitation. This could be explained by the limitation of the analog method to extrapolate unobserved precipitation records. These results suggest that the MOS-Analog is a spatially consistent alternative to standard bias correction methods, although the limitation for extreme values should be taken with caution in cases where this aspect is relevant for the problem.

Article: http://onlinelibrary.wiley.com/doi/10.1002/2016JD025724/abstract

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