1. Introduction
Research on Applied Climatology has focused on two main lines: one envisages the atmosphere as a risk system capable of endangering the natural environment and human activities, while for the other, the atmosphere is a natural resource for human development [
1]. Tourism Climatology is included within the latter.
Tourism has become one of the most important economic activities in many countries and has been under continuous expansion over the past several decades, playing a relevant role in promoting the development of national economies [
2]. Although there are multiple factors explaining the diversity of touristic activities, it is no less true that weather and climate resources play a relevant role on specific typologies.
Climate is undoubtedly the most important resource for most 3S (sand, sea, and sun) destinations. It directly drives the main intra- and interregional travel flows (mostly from temperate to subtropical and tropical regions), significantly influencing the number of visits [
3]. Moreover, climate also regulates other natural assets, such as beach environments, land- and seascapes or regional biodiversity, supplementary natural resources which are additional attraction factors that improve the visitor’s satisfaction levels.
Unlike “climate-dependent” destinations, such as the Mediterranean, ‘weather-sensitive’ destinations are those in which climate is not a tourist resource itself. According to Smith’s scheme [
4,
5], beach visitors in ‘weather sensitive’ destinations used to accommodate their activities to the variable daily weather conditions; most of them could be categorized as ‘day-trippers’, i.e., they reside relatively close to the coast, visiting beaches if the weather meets their expectations, but shifting to alternative activities otherwise. Flexibility to adapt plans and opportunism to take advantage of weather conditions for bathing are key concepts for those visitors. The Atlantic seaboard of southwestern Europe can be included well into the category of “weather-sensitive” beach destinations because beach attendance is linked to clear skies and the lack of rainfall [
6,
7,
8,
9,
10]. The region includes several resorts (e.g., La Toja, Santander and San Sebastian in Spain; Biarritz, Ille of Ré in France; and Brighton in the UK) whose long touristic traditions, linked to the “sea bathing” therapies among wealthiest, goes back to the middle of the 19th century. Despite a lower volume of visitors in comparison with the Mediterranean coast, tourism represents an important income source for those regional economies and evidence differentiating features. For example, 87% of the visitors who arrive to Cantabria (N. Spain) are domestic travelers, mostly as familiar units, spending no more than a week and using housing renting, camping or rural hotels [
11].
Movement restrictions between countries caused by COVID-19 drastically interrupted international travel, causing massive drops in the arrival of tourists to the main international 3S destinations. In return, movements to domestic destinations increased substantially. Despite the progressive easing of travel restrictions, a return to pre-pandemic conditions does not seem likely, at least in the coming years [
12,
13]. Images of July 2020, when an anomalous hot and dry period took place across Western Europe, showed crowded beaches on the SE coast of the UK and NW France, traffic jams, water supply difficulties in locations of Northern Spain, etc. These problems can be considered a good preview of future scenarios linked to the increase in global temperatures. Studies focused on tourism activities and climate change advise of a deterioration of the future climatic conditions during the current peak demand season in the Mediterranean, whereas improving in central and northern Europe [
14,
15,
16,
17,
18]. Tourists coming from the latter regions may not travel so far if enjoying more appealing summer climatic conditions at home, thus preferring domestic rather than Mediterranean emplacements. Thus, changes in the length, seasonality, and quality of the resource for highly dependent climate tourist activities (i.e., beach-based tourism) could have important implications for competitive relationships among destinations and their profitability, and the potential consequences of climate change may be relevant not only in the destination countries, but also in countries of origin [
19,
20,
21,
22]. Moreover, such massive inflow of visitors might potentially impact severely different natural and human activities upon coastal areas which have not experienced the same human pressure suffered by the Mediterranean coasts.
In the context of climate beach-based tourism studies, the aptitude of a destination to meet the weather expectations of beach users can be evaluated through climate indices. It appears that Mieczkowski’s Tourism Climate Index (TCI) is still the most applied empirical index in multiple destinations and tourist segments [
23]. Despite successive adaptations for beach tourism (e.g., Beach Climate Index—BCI—[
24]; Modified Climate Index for Tourism—MCIT—[
25]), none of them have not been tested from declared or revealed preferences. To overcome that deficiency, the Holiday Climate Index from 3S tourism (HCI: Beach; [
26,
27]) has been designed specifically to evaluate the recreational beach segment. The HCI: Beach integrates the thermal, physical, and aesthetic facets of the climatic variables relevant for this kind of tourism segment [
28], its calculation is simple, and it has been tested empirically. It also recognizes the non-linear impact of certain variables on beach attendance, since both declared and stated preference studies emphasize clear skies and the lack of rain as the best weather conditions for beach attendance [
8,
9,
10,
29,
30,
31]. Therefore, the HCI: Beach also includes a penalizing function to account the overriding role of variables such as rain and wind speed. In addition, it assumes higher thermal thresholds, due to the resilience of bathers to conditions that could be classified as thermal stress in other activities [
32,
33]. The HCI: Beach has been applied to different destinations and climatic settings, to characterize both current and future conditions [
34,
35,
36]. However, to date, the HCI: Beach index has not been used to assess its long-term variability or its links with atmospheric circulation, unlike other bioclimatic indices [
37,
38,
39,
40,
41,
42]. Characterizing the climate beach-based tourism aptitude on a regional-scale basis, as observed in the instrumental record, is a necessary initial step toward making meaningful assessments of the accuracy of regional climate predictions. Furthermore, a process-based understanding of the causes of low-frequency variability in regional climates may improve future medium- to long-range regional forecasting capabilities. Additionally, the study of the interannual variability and trends is important in the context of the ongoing climatic change, which may significantly affect the frequency and duration of specific weather conditions, favorable to the development of a given leisure activity.
Consequently, the main objective of this contribution is to analyze the current climate beach-based tourism aptitude along the Atlantic Coast of SW Europe and its recent decadal evolution using the HCI: Beach index. With such an objective in mind, (1) the main spatial and temporal features are described; (2) its temporal evolution since 1973 till 2017 is analyzed and (3) linked with the recent evolution of the atmospheric circulation at different scales.
4. Discussion
The climate aptitude for beach-based tourism along the Atlantic coast of SW Europe has experienced variations in time and space during the period 1973–2017. That variability has been studied using a state-of-the-art climate tourism index; the HCI: Beach index, which considers the different climatic facets of the tourist activity and the constraining impact of specific variables, has been used.
The spatial distribution of the summer values (July and August) shows a pattern controlled by latitude, although regional anomalies exist, related to the orientation of the coast regarding the prevailing circulation patterns and the presence of mountains near the coast. Thermal variables show the closest links with latitude, as result of the differences on solar radiation reception and surface heat budget. Additionally, physical variables such as wind speed and frequency of precipitation also display a significant correlation with latitude since the proximity to the main Atlantic storm track favors a greater frequency of frontal systems. Cloudiness and total precipitation, the two variables with greater weight on HCI: Beach index, do not show the same clear spatial pattern, because orography and warm sea surface temperatures tend to intensify precipitation. Consequently, that overall pattern shows distortions at various points. For example, along the English Channel, climate tourist aptitude rapidly changes from W to E, from minimum values in Cornwall/Brittany and to a maximum in Kent/Cote d’Opal. A dissymmetry is also observed between the UK and the French sides since most of the positive anomalies appear in the former. Frontal systems linked to storms crossing well above the 55° N parallel (W, NW and A LWTs) experience a progressive weakening towards the E during its eastward progression, placing the UK coast on the leeward and the French coast on the windward.
Another singularity is found in the Gulf of Biscay area, encompassing the Cantabrian and Aquitanian coasts. Due to the proximity of the Cantabrian Range and Pyrenees to the coastline, orographic cloudiness is very common in this area, even under stable atmospheric conditions, being capable of reducing the overall values of the HCI: Beach index. In addition, the development of a summer warm SST pool in the SE corner of the Gulf of Biscay provides abundant latent heat to the lower layers of the atmosphere, which, in conjunction with upper-level lows, generates convective episodes of intense rainfall events [
51].
On the contrary, positive anomalies are observed across the western French coast (departments of Loire-Atlantique, Vendeé and Charente-Maritime), as well as along Galicia and Northern Portugal. The lack of any kind of topographical obstacle, beyond the own coast, in the first case, and the upwelling phenomenon in the second, explain the predominance of sunnier, drier, and warmer conditions, and, consequently, the higher values of HCI: Beach.
When comparing regional HCI: Beach values with the variability of LWT, a better predictive capacity has been found for the northernmost region. The proximity to the main summer Atlantic storm track means that, even in summertime, daily weather mechanisms are those typical of the mid-latitude systems. Extratropical cyclones, accompanied by frontal systems provide clouds, winds and rain (SW, W, NW, and N LWTs), while anticyclones (types E, SE and A types) cause fair weather. Indeed, convection exists within the frontal structures but is limited in time and space by the movement of the fronts. Southward, the 45° N parallel becomes a transition zone between the temperate and subtropical (Mediterranean climates). In this region, LWTs can explain a great portion of the variability of the HCI index since the most significative are also related to extratropical cyclones. However, only a few disturbances reach the area in summer, due to the greater distance to the main storm track. Consequently, the predictive capability of the LWTs diminishes in comparison with the UK and Northern France. Finally, the lowest predictive capability of LWTs is found along the northern Coast of Spain. The closest related patterns to HCI: Beach are a mixture of stable (e.g., S, SW, E and A) and unstable (N). It has been mentioned that, even during stable conditions, any northerly flow can develop a stratocumuli layer when reaching the mountains, which considerably reduces the values of the index at the coast. Additionally, the intensity of the precipitation can be substantially diverse, depending on the convective mechanisms triggered by the combination of a moist and warm surface layer (moisture transference from the warm sea water pool) and an upper cool air mass.
Summarizing, in UK and France most of the variability can be explained by regional and hemispheric processes, while in Portugal, Spain and southern France there is a larger dependence on local processes, which are more difficult to account at the scale and diagnostic tools used in this paper.
The absence of clear trends in the summer HCI: Beach index seem surprising in the context of the ongoing global warming. However, the most recent IPCC report confirms that the global warming trends are spatially, seasonally and daylight dependent [
52]. Indeed, a great number of stations show trends towards high maximum temperatures, but the only coherent regional signal showing a significant warming is the Northern coast of the Iberian Peninsula. Although a more in-depth analysis of the origin of this trend is needed, it should be noted that southerly flows, identified as weather types prone to excellent HCI: Beach ratings, not only direct warm air masses over the Iberian Peninsula, but also add an additional warming when descending along the northern slope of the Cantabrian Mountains and Pyrenees, because of the thermodynamic transformations associated with the Föhn effect. However, this warming trend is balanced by the lack of any significant trend in cloudiness and precipitation, which are the variables that load the most in HCI: Beach.
In the rest of the regions, a coherent significant warming signal is not so clear, and most trends are weaker and, occasionally, non-significant. This may respond, in the first instance, to the coastal location of the stations, where the influence of the sea might weaken the trends observed in mainland stations (the weakest appear on stations placed on islands). The most stable and sunny situations, conductive to high HCI: Beach values, often generate sea breeze regimes, triggered by the thermal contrast between marine and continental surfaces. Those sea breezes direct cool and moist air masses to a narrow coastal strip, submitted to a slight cooling with respect to the mainland areas. Furthermore, it is not unknown that, if a very warm advection develops, the atmospheric layers directly in contact with the coastal waters become saturated; the increase in water vapor may create advection fogs, also affecting the weather conditions of the coastal strip [
53,
54]. Additionally, that thermal comfort (whose input is the HUMIDEX index) only represents one third of the total weight upon HCI: Beach, while cloudiness represents 40% and precipitation another 30%. Recent trends on climate beach-based tourism aptitude have been analyzed for different world locations and with different indices. Those results empirically support the assertion that climate change is unequally impacting the re-distribution of climate resources dependent on climate region and specific geographical characteristics. For example, the mid-latitude region of USA experienced the largest improvement from 1981 to 2019, while just a moderate improvement or even a decline was observed in the tropical and arid climate regions [
39]. A significant lengthening of the annual average tourist climate comfortable period in mainland China was also found for the 1981–2010 period [
40]. On the other side, trends of TCI scores did not indicate a significant change for the majority of South Africa [
41], as well as in the Canary Islands [
42], without any significant trend to worsening due to increased temperatures in both subtropical destinations.
The close connection between the interannual variability of both variables in the Atlantic N region with the phase and intensity of the summer NAO [
55,
56] has favored the occurrence of mild, cloudy, and wet summers, particularly from 2000 onwards [
57]. As with its winter counterpart, the summer NAO has shown positive (e.g., 2013, 2006, 1995, 1983, 1976 and 1975) and negative phases (e.g., 2007, 2008, 2009, 2011, 2012 and 2015). Positive phases correspond to warm, dry, and sunny summers, while negative phases tend to be associated with cool and wet summers. For example, UK summers have been on average 11% wetter than 1981–2010 and 13% wetter than 1961–1990 during the decade 2009–2018 [
58].