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In a unique study, Luna (Luna, Sci Rep 10:1–10, 2020) examined the viability and germination of 12 hard-seeded Cistaceae in the Mediterranean Basin by alternating a prolonged summer-type temperature (50/20 °C at 12 h cycles) treatment with a fire-type heat pulse. A re-analysis of their data shows that the summer treatment applied before the heat pulse was superfluous as similar high levels of germination under ambient conditions were attained with the heat pulse only. Additional tests using the hard seeds of Acacia showed that the water gap opened at once in the presence of dry heat such that contact with moisture is not required to complete the process of softening. The abundance of hard seeds remaining when the summer treatment was applied after the heat pulse is better explained by ungerminated seeds having become hard again under such dry conditions rather than remaining dormant, i.e., acquiring secondary physical dormancy, and thus becoming 'desensitized' to their environment. While this response may be adaptive, such a retarding effect will be limited in practice as most fires are expected in autumn, at least historically, and are thus close to the start of optimal winter conditions for germination. Future studies should concentrate on the fate of the water gap plug during such alternating treatments and also ensure that realistic summer temperature regimes are used. [ABSTRACT FROM AUTHOR]

Extreme-temperature events have a great impact on human society. Thus, knowledge of summer temperatures can be very useful both for the general public and for organizations whose workers operate in the open. An accurate forecasting of summer maximum and minimum temperatures could help to predict heatwave conditions and permit the implementation of strategies aimed at minimizing the negative effects that high temperatures have on human health. The objective of this work is to evaluate the skill of the regional atmospheric and modelling system (RAMS) model in determining daily summer maximum and minimum temperatures in the Valencia Region. For this, we have used the real-time configuration of this model currently running at the Centro de Estudios Ambientales de Mediterráneo Foundation. This operational system is run twice a day, and both runs have a 3-day forecast range. To carry out the verification of the model in this work, the information generated by the system has been broken into individual simulation days for a specific daily run of the model. Moreover, we have analysed the summer forecast period from 1 June to 31 August for 2007, 2008, 2009 and 2010. The results indicate good agreement between observed and simulated maximum temperatures, with RMSE in general near 2 °C both for coastal and inland stations. For this parameter, the model shows a negative bias around −1.5 °C in the coast, while the opposite trend is observed inland. In addition, RAMS also shows good results in forecasting minimum temperatures for coastal locations, with bias lower than 1 °C and RMSE below 2 °C. However, the model presents some difficulties for this parameter inland, where bias higher than 3 °C and RMSE of about 4 °C have been found. Besides, there is little difference in both temperatures forecasted within the two daily RAMS cycles and that RAMS is very stable in maintaining the forecast performance at least for three forecast days. [ABSTRACT FROM AUTHOR]

A single colony of the non-native grass Poa pratensis L., which was introduced inadvertently to Cierva Point, Antarctic Peninsula, during the 1954-1955 season, was still present during a survey in February 2012, making it the longest surviving non-native vascular plant colony known in Antarctica. Since 1991, the grass cover has roughly tripled in size, with an annual increase in area of approximately 0.016 m, and an estimated maximum radial growth rate of 1.43 cm y. However, it remains restricted to the original site of introduction and its immediate surroundings (c. 1 m). Annual flowering of the plants occurred during the 2010/2011 and 2011/2012 seasons; however, there has been no seed production and only incomplete development of the sexual structures. Current environmental conditions, including low temperatures, may inhibit sexual reproduction. Lack of effective vegetative dispersal may be influenced by the low level of human activity at the site, which limits opportunities for human-mediated dispersal. Although P. pratensis has existed at Cierva Point for almost 60 years, it has not yet become invasive. Scenarios for the potential future development of the species in Antarctica and the associated negative impacts upon the native vegetation from competition are discussed in the context of regional climate change. Finally, we describe the environmental risk presented by P. pratensis and argue that this non-native species should be eradicated as soon as possible in accordance with the Protocol on Environmental Protection to the Antarctic Treaty. [ABSTRACT FROM AUTHOR]

The occurrence and intensity of heatwaves is expected to increase with climate change. Early warnings of hot summers have therefore a great socio-economical value. Previous studies have shown that hot summers are preceded by a Southern European rainfall deficit during winter, and higher spring temperatures. Changes in the surface energy budget are believed to drive this evolution, in particular changes in the latent and sensible heat fluxes. However these have rarely been investigated due to the lack of long-term reliable observation data. In this study, we analyzed several data-derived gridded products of latent and sensible heat fluxes, based on flux tower observations, together with re-analyses and regional climate model simulations over Europe. We find that warm summers are preceded by an increase in latent heat flux in early spring. During warm summers, an increase in available energy results in an excess of both latent and sensible heat fluxes over most of Europe, but a latent heat flux decrease over the Iberian Peninsula. This indicates that, on average, a summertime soil-moisture limited evapotranspiration regime only prevails in the Iberian Peninsula. In general, the models that we analyzed overestimate latent heat and underestimate sensible heat as compared to the flux tower derived data-product. Most models show considerable drying during warm seasons, leading to the establishment of a soil-moisture limited regime across Europe in summer. This over-estimation by the current generation of models of latent heat and hence of soil moisture deficit over Europe in summer has potential consequences for future summertime climate projections and the projected frequency of heat waves. We also show that a northward propagation of drought during warm summers is found in model results, a phenomenon which is also seen in the flux tower data-product. Our results lead to a better understanding of the role of latent and sensible heat flux in summer heatwaves, and provide a framework for benchmark of modeling studies. [ABSTRACT FROM AUTHOR]

In this paper, we present a 392-year-long preliminary temperature reconstruction for western Hungary. The reconstructed series is based on five vine- and grain-related historical phenological series from the town of Kőszeg. We apply dendrochronological methods for both signal assessment of the phenological series and the resultant temperature reconstruction. As a proof of concept, the present reconstruction explains 57% of the temperature variance of May-July Budapest mean temperatures and is well verified with coefficient of efficiency values in excess of 0.45. The developed temperature reconstruction portrays warm conditions during the late seventeenth and early eighteenth centuries with a period of cooling until the coldest reconstructed period centred around 1815, which was followed by a period of warming until the 1860s. The phenological evidence analysed here represent an important data source from which non-biased estimates of past climate can be derived that may provide information at all possible time-scales. [ABSTRACT FROM AUTHOR]