Precipitation Modes in the Spanish Mountains and Sensitivity of Snow Cover
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Reg Environ Change DOI 10.1007/s10113-012-0380-8 ORIGINAL ARTICLE Evolution and frequency (1970–2007) of combined temperature– precipitation modes in the Spanish mountains and sensitivity of snow cover Enrique Mora´n-Tejeda • Sixto Herrera • J. Ignacio Lo´pez-Moreno • Jesu´s Revuelto • Anthony Lehmann • Martin Beniston Received: 13 July 2012 / Accepted: 18 November 2012 Ó Springer-Verlag Berlin Heidelberg 2012 Abstract Snow cover in Spanish mountains is crucial for Keywords Precipitation Á Temperature Á Joint-quantile ensuring water availability in spring and summer months, indices Á Spain02 Á Snow Á Mountains Á Iberian Peninsula for the success of winter tourism or for the maintenance of biodiversity in mountain ecosystems. A changing climate may affect the volume of snow cover even in high moun- Introduction tains, where weather conditions are usually favorable for snow accumulation. In this paper, we aim to investigate the Snow cover in mountains is a natural resource that is of evolution (1970–2007) of combined precipitation–temper- high ecological, socio-economic and scientific value. The ature modes in the Spanish mountains, and the sensitivity mountain snowpack constitutes the primary source of water of the snowpack to their occurrence. The climatic database in many areas, ensuring water supply to the lowlands even ‘‘Spain02’’ and snow thickness data for Spanish mountains during the dry season (Barnett et al. 2005; Knowles et al. were used for this purpose. Results showed that the fre- 2006). But snow cover in mountains has many other quency of dry-warm and wet-warm days has increased over implications, including the functioning of alpine and sub- time in all mountain ranges, while the frequency of the alpine ecosystems (Pauli et al. 2003; Keller et al. 2005)or ‘‘cold’’ modes has decreased. The thickness of the snow- the financial success of ski resorts (Elsasser and Bu¨rki pack in the Pyrenees has also decreased and its evolution is 2002). In the mountains of the Iberian Peninsula, under the negatively correlated with the frequency of dry-warm days, predominant influence of Mediterranean climates, the and positively correlated with the frequency of dry-cold environmental and economic role of snow can in some and wet-cold days. This work constitutes the first approach years be critical. This is due to the highly variable thick- that relates the evolution of climatic conditions favorable ness of the snowpack related to the characteristic inter- or unfavorable for snow accumulation and the evolution of annual variability of precipitation (Lo´pez-Moreno 2005). the snowpack in Spanish mountains. The accumulation of snow cover is a process that is highly dependent on particular weather conditions. These clearly include the combination of precipitation and below- zero temperatures for triggering the snowfall and the per- sistence of low temperatures during a reasonably long E. Mora´n-Tejeda (&) Á A. Lehmann Á M. Beniston period that enables a sustained snowpack (Beniston et al. Institute for Environmental Studies, University of Geneva, 2011;Lo´pez-Moreno et al. 2011). These conditions are Site de Battelle, Baˆtiment D, 7 route de Drize, characteristic of mountains. Their topography favors the 1227 Carouge, Switzerland e-mail: [email protected]; [email protected] gradients of temperature such that the zero-degree isotherm can be reached at certain elevations, as well as enhanced S. Herrera precipitation due to the uplift of moist air (Barry 2005). Predictia Intelligent Data Solutions, S.L., Santander, Spain Knowledge of the type of meteorological conditions that J. Ignacio Lo´pez-Moreno Á J. Revuelto prevail in mountains during the snow accumulation and Pyrenean Institute of Ecology, CSIC, Zaragoza, Spain melting seasons is therefore essential to predict the 123 E. Mora´n-Tejeda et al. accumulation of the snowpack as well as the subsequent mutual feedbacks that both temperature and precipitation availability of water resources. However, snow-prone may exert upon each other. This approach was shown to be weather conditions might be threatened in mountain useful as a proxy for predicting the evolution of snowpack regions as a result of greenhouse gas induced warming in the Alps (Beniston et al. 2011), because particular (Beniston 2003). There is wide agreement that mean tem- combinations of temperature and precipitation are closely peratures have increased globally during the last 40 years, related to the synoptic circulations favorable (or not) for in relation to the observed increases in radiatively active snowy winters. We believe that this method can also be greenhouse gases (IPCC 2007; Solomon et al. 2007). applied to the mountains of southern Europe and thus its Global warming is responsible for the retreat of glaciers in performance when applied to Spanish mountains will be different parts of world, as well as for the reduction in the examined in this work. snowpack in mountains (see examples in Beniston 2003). Based on the above considerations, the objective of this In Europe, the Alps have been extensively studied in terms paper is to study the evolution and trends of combined of the effects of climate variability on snow cover (Ben- precipitation and temperature quantile-based indices in the iston et al. 2003, 2011; Uhlmann et al. 2009), and most mountain ranges of the continental Spain during the last studies highlight a reduction in the snowpack due to war- three decades. The underlying hypothesis is that long-term mer conditions, both in the past and projected for coming changes of moisture and temperature in mountains may decades. Similar conclusions were drawn for the mountains trigger significant changes in thickness of the snowpack. of the western US and Canada, where snow also constitutes We thus also seek to examine the relation of the observed a primary source of water resources (Hamlet et al. 2005; evolution in climate indices with that of the snowpack Knowles et al. 2006). during winter and spring seasons. This work constitutes the There is a clear need for research in other mountains of first assessment of climate evolution in Spanish mountains Europe, due to their role as ‘‘climatic islands,’’ such as in relation to snow accumulation. The results will then those in the Mediterranean basin (Lo´pez-Moreno et al. form the basis for understanding the future evolution of the 2011). In the Iberian Peninsula, various studies highlighted snowpack in the Iberian mountains in a changing climate. changes in the seasonality of mountain river flows, which have been attributed to reduced snowpack (Lo´pez-Moreno et al. 2008; Mora´n-Tejeda et al. 2011). Contrary to tem- Study area perature, precipitation has not exhibited a homogeneous trend signal around the world. Some regions, including the The areas of research are the main mountain chains in Mediterranean, are expected to experience drier conditions continental Spain. The most important mountain ranges, on the future decades (Milly et al. 2005; IPCC 2007). To with elevations generally over 2,000 m, are the Pyrenees, date, however, there has been no clear trend toward more the Central System, the Cantabrian Range, the Iberian or less precipitation in Mediterranean countries (Blade´ and System and the Baetic System (Fig. 1a). The latter range is Castro-Dı´ez 2010). the one with the highest altitude of the Iberian Peninsula, Given the specific meteorological conditions for snow- namely the Mulhacen Peak (3,478 m). The geographical fall, that are seasonally dependent in mid-latitudes, studies disposition of the Iberian Peninsula, located between the pertaining to the behavior of snow can be placed within the Atlantic and the Mediterranean, together with the complex study of climatic extremes, that is, the values of the cli- topography, induces a notable variety of climates matic variables located within the tails of the frequency throughout the territory. A northwest–southeast gradient of distributions. Much effort has been made in recent years to precipitation and temperature is observed, with Atlantic characterize the behavior of extremes, as exemplified by climate conditions (precipitation over 1,000 mm/year and the number of indices recommended by the World Mete- cool temperatures) in the northwestern quadrant, semi-arid orological Organization Commission for Climatology conditions (precipitation less than 300 mm/year and warm (CCl) jointly with the World Climate Research Programme temperatures) in the southwest and variants of Mediterra- (WCRP) project on Climate Variability and Predictability nean climates in between. Precipitation is concentrated (CLIVAR) (see examples in Alexander et al. 2006). These mainly in winter (DJF with about 40 %), when minimum indices are derived from series of daily precipitation and temperatures usually drop to 0 °C or below, depending on temperatures, and in general, they characterize one single the elevation. Thus, snowfalls are frequent especially in the variable (e.g., warm days, heavy precipitation days, etc.), mountainous areas where a deep snowpack usually accu- but their statistical calculation also enables different vari- mulates. Warmer conditions in spring trigger the melting of ables to be combined. Beniston (2009) demonstrated that the snowpack, with a lag in time for different mountain the use of joint-quantile indices can provide new insights systems, ranging from late March to early June depending for the understanding of climate variability, due to the on the elevation and latitude. 123 The Spanish mountains