Snow trends in Northern Spain: analysis and simulation with statistical downscaling methods

Abstract

ABSTRACT:In this study we analyze and simulate (with statistical downscaling techniques) the snow trends observed in the Northern Iberian Peninsula using daily snow occurrence (DSO) data from a network of 33 stations ranging from 60 to 1350 m. We first analyze the annual snow frequency measured as the annual number of snow days (NSD), obtaining a significant decreasing trend since the mid-seventies with a NSD reduction of about 50%; moreover, this magnitude is similar for low and high stations and for winter and spring separately. Then, we analyze the existing correlations with mean temperature and precipitation occurrence obtaining different relationships depending on the season and elevation. Finally, we simulate the observed trends using the connection of DSO with large-scale fields simulated by a General Circulation Model; for this purpose we apply an analog-based statistical downscaling method to obtain an estimation of DSO, working in perfect prognosis conditions using reanalysis data. On the one hand, the downscaling method is able to estimate/predict the DSO with typical values of hit and false alarm rates around 60% and 2%, respectively. On the other hand, the annual frequency obtained by averaging the DSO estimations reproduces very well both the observed trends and the high inter-annual variability. These promising results open the possibility to future research in seasonal or climate change projections of snow frequency.

Assessment of snowfall accumulation underestimation by tipping bucket gauges in the Spanish operational network

“…on the slopes). However, in terms of the total water equivalent that is not accounted for, it is likely the northern areas and the Pyrenees range experience more total undercatch because of the relatively large portion of winter precipitation occurring in these mountains as snowfall (Pons et al, 2010;Bootey et al, 2013;Buisan et al, 2014). It is also important to note that, in general, snowfall in Spain occurs very infrequently at temperatures colder than −3 • C, and the average 1 h wind speed during snowfall events is lower than 30 km h −1 .…”

“…Within the Spanish climate record, winter precipitation is persistently underestimated, especially in areas subject to frequent snowfall (Pons et al, 2010;Buisan et al, 2014). This underestimation could affect previous studies of solid precipitation, especially if the period of time considered was associated with significant winter precipitation extremes Vicente-Serrano et al, 2011;Añel et al, 2014;Cortesi et al, 2014;Buisan et al, 2016a).…”

“…The locations with more winter precip-itation on average are located north of the Cantabrian Range and in the westerns areas of the Pyrenees (Pons et al, 2010;Bootey et al, 2013;Buisan et al, 2014). The selection of specific AWS within this area was limited to those for which the TPB and anemometer were heated, and the number of hourly snowfall events was greater than 75.…”

The contrasted evolution of high and low flows and precipitation indices in the Duero basin (Spain)

“…Recent studies have demonstrated a negative trend in the occurrence of snow days in the northwest of the Iberian Peninsula (Pons et al 2009), and a substantial decrease in the duration and depth of the snowpack, which is causing a decrease and shift in spring peak flows (López-Moreno 2005, López-Moreno et al 2008. Snowmelt is a general component of river regimes in the headwaters of the Duero basin (Morán-Tejeda et al 2011b), and the decrease of spring high flows is likely to be related to the reduction in snowpack given the increasing temperatures documented in the region in recent decades.…”

An updated review on recent trends in observational surface atmospheric variables and their extremes over Spain

“…Overall, results are inconclusive and seem to be highly affected by the period of analysis. Pons et al (2010) analysed snow trends in northern Spain using daily snow occurrence data from a network of 33 stations. They showed a significant decreasing trend in the annual number of snow days since the mid-1970s to 2001, with a reduction of about -50%.…”