The altitudinal temperature lapse rates applied to high elevation rockfalls studies in the Western European Alps

To know the vertical distribution of air temperature is complex, and this is necessary for different applications. The main explanatory variable of air temperature is elevation above sea level, whose relationship with air temperature is measured by air temperature lapse rates (LRs). LRs can vary considerably spatiotemporally due to a wide spectrum of geographical, environmental, and other atmospheric factors. Our study presents the first comprehensive assessment of spatiotemporal changes of LRs over the Tropical Andes. Our study is focused on the Peruvian and Ecuadorian Andes, divided in two subregions by the parallel 9.5° (i.e., north and south). Maximum and minimum air temperatures were employed from 115 quality checked weather stations, for the period 1994–2011. Maximum (LRmax) and minimum (LRmin) air temperature lapse rates have been calculated for the whole study period. The effects of seasonality, humidity content and ENSO on the variability of LRs have been analysed. Results show that LRs have large spatiotemporal variability, since references values of LRmax range from −3.57 (South, dry season) to −4.77 (North, wet season), and LRmin range from −3.78 (North, dry season) to −4.93°C·km−1 (South, dry season), in function of season and subregion. Results indicate that the ENSO phases contribute significantly to the variability of southern subregion LRs. This study also presents that minimum air temperatures were more unpredictable than maximum air temperatures in terms of error and uncertainty, as a consequence of the larger spatial variability of nocturnal air temperatures, mainly influenced by local topography. In conclusion, this work goes deeper into the need to obtain precise LRs adapted to the study region, and shows that the use of standard LR values can cause significant failures in modelling air temperature in regions of complex terrain, such as the Andes.

Section: Introductionmentioning

confidence: 99%

Maximum and minimum air temperature lapse rates in the Andean region of Ecuador and Peru

Navarro-Serrano

López‐Moreno

Domínguez‐Castro

et al. 2020

“…Several studies have reported significant temporal variability in NSLR at daily and seasonal scales in various mountain regions including the Rocky (Kunkel, ; Pepin and Losleben, ; Blandford et al, ) and Appalachian (Bolstad et al ., ) mountains in the United States, in China (Fang and Yoda, ; Tang and Fang, ; Du et al, ), the Himalayan mountains (Kattel et al, ; Immerzeel et al, ), the Alps (Rolland, ; Dumas, ; Kirchner et al, ; Nigrelli et al, ), and polar areas (Marshall et al ., ). These studies have reported steeper NSLRs under unstable atmospheric conditions, and marked differences in NSLR have been found as a function of synoptic conditions (Pepin et al, ; ; Pepin, ; Blandford et al, ; Holden and Rose, ; Kirchner et al, ; Miró et al, ).…”

Section: Introductionmentioning

confidence: 99%

Estimation of near‐surface air temperature lapse rates over continental Spain and its mountain areas

Navarro-Serrano

López‐Moreno

Azorín-Molina

et al. 2018

Although the mean environmental lapse rate (MELR) value (a linear decrease of −6.5 °C/km) is the most widely used, near‐surface (i.e., non‐free atmosphere) air temperature lapse rates (NSLRs; measured at ~1.5 m height) are variable in space and time because of their dependence on topography and meteorological conditions. In this study we conducted the first analysis of the spatial and temporal variability of NSLRs for continental Spain and their relationship to synoptic atmospheric circulation (circulation weather types [CWTs]), focusing on major mountain areas including the Pyrenees, Cantabrian, Central, Baetic, and Iberian ranges. The results showed that the NSLR varied markedly at spatial and seasonal scales and depended on the dominant atmospheric conditions. The median NSLR values were weaker (less negative) than the MELR for the mountain areas (Pyrenees −5.17 °C/km; Cantabrian range −5.22 °C/km; Central range −5.78 °C/km; Baetic range −4.83 °C/km; Iberian range −5.79 °C/km) and for the entire continental Spain (−5.28 °C/km). For the entire continental Spain the steepest NSLR values were found in April (−5.80 °C/km), May (−5.58 °C/km), and October (−5.54 °C/km) because of the dominance of northerly and westerly advections of cold air. The weakest NSLR values were found in July (−4.67 °C/km) and August (−4.78 °C/km) because of the inland heating, and in winter because of the occurrence of thermal inversions. As the use of the MELR involves the assumption of large errors, we propose 1 zonal, 12 monthly, 11 CWTs, and 132 hybrid monthly–CWTs NSLRs for each of the mountain ranges and for the entire continental Spain. More regional studies are urgently needed to accurately assess the NSLR as a function of atmospheric circulation conditions.

“…As a first point of discussion, it should be noted that the values of TLR are extremely variable in time and space (Rolland, 2002;Otto-Bliesner et al, 2006;Minder et al, 2010;Prömmel et al, 2010;Dumas, 2013;Li et al, 2015). This gives credence to the idea that, in reality, the situation is much more complicated than the simple average theoretical decrease of 0.6 C/100 m elevation (Nigrelli et al, 2017). Some studies in the Alps report that the monthly variation of TLRs is similar to that of tx, with the lowest values observed in winter and the highest in spring or summer (De Saintignon, 1976; Douguédroit and De FIGURE 5 Variation of the monthly mean R 2 for tn (a) and tx (b) and temperature lapse rate for tn (c) and tx (d), for five of the 10 resolutions Saintignon, 1984;Bisci et al, 1989;Rolland, 2002;Dumas and Atunes, 2003;Dumas, 2013;Joly et al, 2017).…”

Section: Tlr Variationmentioning

confidence: 91%

Influence of spatial information resolution on the relation between elevation and temperature

Joly

Castel

Pohl

et al. 2018

The association between elevation and temperature is analysed by simple linear correlations across several spatial scales. The minimum (tn) and maximum (tx) temperatures (response variables), expressed at two time scales (monthly and daily), are observed for 102 weather stations in east central France from 1980 to 2014 (12,784 days). Elevation (explanatory variable) is provided at 10 resolutions: 50, 100, 200, 500 m, 1, 2, 4, 8, 12, and 16 km. The coefficient of determination, R2, is used to determine which resolution gives the best results. The slope given by the regression is used to assess the drop in temperature per unit of elevation (temperature lapse rate [TLR]). In most situations, monthly and daily temperatures are optimally explained by the finest (50 m) resolution: the R2 is, respectively, 0.53 and 0.24 for tn and 0.78 and 0.39 for tx. The coarser resolutions produce results of much lower quality. However, in one circumstance (monthly mean of tn), the highest R2 value is obtained for the 4‐km resolution, which is a meaningful result as current regional climate models now achieve similar resolutions. Both monthly and daily TLRs of tn and tx are, on average, slightly lower than −0.5 °C/100 m at 50‐m resolution. The TLR decreases with resolution: it is only −0.23 °C/100 m for tn and −0.13 °C/100 m for tx at 16‐km resolution. Other insightful results involve the influence of the topographical context, which shows some additional effect with that of elevation and which was quantified through partial correlations.