Sorin Cheval

The summer surface urban heat island of Bucharest (Romania) retrieved from MODIS images

The summer surface urban heat island (SUHI) of the city of Bucharest (Romania) is investigated in terms of its shape, intensity, extension and links to land cover. The study employs land surface temperature (LST) data retrieved by the Moderate Resolution Imaging Spectroradiometer (MODIS) sensors aboard the Terra (EOS AM-1) and Aqua (EOS PM-1) NASA satellites, between 2000 and 2012. Based on the Rodionov regime shift index, the significant changing points in the land surface temperature values along transverse profiles crossing the city’s centre were considered as SUHI’s limits. The thermal difference between the SUHI and several surrounding buffers defines the SUHI’s intensity. The night-time SUHI’s geometry is more regular, and its intensity is slightly lower than during the day, while the land cover exerts a strong influence on Bucharest’s LST. In summary, the study proposes a methodology to delimit and quantify the average SUHI based on the statistical significance of the shift between the urban area and its surroundings, and the limitations of the method are mentioned.

Accuracy and sensitivity analysis for 54 models of computing hourly diffuse solar irradiation on clear sky

Fifty-four broadband models for computation of solar diffuse irradiation on horizontal surface were tested in Romania (South-Eastern Europe). The input data consist of surface meteorological data, column integrated data, and data derived from satellite measurements. The testing procedure is performed in 21 stages intended to provide information about the sensitivity of the models to various sets of input data. There is no model to be ranked “the best” for all sets of input data. However, some of the models performed better than others, in the sense that they were ranked among the best for most of the testing stages. The best models for solar diffuse radiation computation are, on equal footing, ASHRAE 2005 model (ASHRAE 2005) and King model (King and Buckius, Solar Energy 22:297–301, 1979). The second best model is MAC model (Davies, Bound Layer Meteor 9:33–52, 1975). Details about the performance of each model in the 21 testing stages are found in the Electronic Supplementary Material.

Climate of the Romanian Carpathians

1. Introduction 2. Theoretical background 2.1 Mountain regions - key issues in environmental research 2.1.1 Mountain regions and climate change 2.1.2 Mountain research in the Carpathian region 2.2 Weather and climate of the Romanian Carpathians: a literature review References 3. Study area 3.1 Geographical location of the Romanian Carpathians within the Carpathian Chain 3.2 General morphological settings 3.3 Paleogeographic evolution and geological constitution 3.4 Hydrology and hydrogeology 3.5 Zonation of vegetation and soils References 4. Data 4.1 Datasets 4.2 Mountain meteorological network References 5. Methods 5.1 Homogenization 5.2 Statistical methods 5.2.1 Mann-Kendall trend test 5.2.2 Kendall-Theil slope estimate 5.2.3 Spearmans rank correlation coefficient 5.3 Spatialization of climatic information 5.4 Regional climate models References 6. Geographical and synoptic control on the climate 6.1 Latitude 6.2 Topography 6.2.1 Altitude 6.2.2 Slope aspect 6.2.3 Slope angle 6.2.4 Landforms 6.3 Regional atmospheric circulation References 7. Regional climatic patterns 7.1 Solar radiation 7.2 Air temperature 7.2.1 Average air temperature lapse rate 7.2.2 Vertical thermal zonation 7.2.3 Annual variation of average temperature 7.2.4 Lapse rates of minimum and maximum temperatures 7.2.5 Spatial distribution of minimum and maximum temperatures 7.2.6 Annual variation of minimum and maximum temperatures 7.2.7 Extreme temperature records 7.3 Precipitation 7.3.1 Vertical zonation and spatial distribution 7.3.2 Wind-induced bias 7.3.3 Annual variation 7.3.4 Precipitation type 7.3.5 Precipitation absolute records 7.4 Wind 7.4.1 Surface wind direction 7.4.2 Surface wind speed 7.4.3 Maximum wind speed 7.4.4 Atmospheric calm 7.4.5 Local winds 7.5 Snowfall and snowpack 7.5.1 Atmospheric circulation patterns related to snowfall events 7.5.2 Snowfall occurrence interval 7.5.3 Snowfall frequency 7.5.4 Snow showers 7.5.5 Snow cover interval 7.5.6 Snow depth 7.5.7 Snow water equivalent References 8. Observed variability trends from instrumental records 8.1 Air temperature 8.2 Precipitation 8.3 Wind 8.4 Snowpack 8.5 Influence of large-scale circulation References 9. Changing climate extremes in the last five decades 9.1 Change in air temperature extremes 9.2 Change in precipitation extremes 9.3 Change in snow extremes References 10. Projections of future changes in climate of the Romanian Carpathians 11. Conclusions Index

Regional Climatic Patterns

This chapter provides a description of the main climatic conditions of the Romanian Carpathians region based on the analysis of the regime of the most important climatic parameters such as air temperature, precipitation, wind and snow. The regional climatic patterns are discussed in terms of elevation effect, influence of the prevailing atmospheric circulation and seasonality, aiming at distinguishing between the climate variation particularities emerging between three main units. The analysis highlights the climatic differentiations between the areas above 800 m and those below 800 m, generally including most of the intra-Carpathian depressions. The absolute climatic records derived from in situ measurements are presented in tabular form.

Geographical and Synoptic Controls on the Climate

This chapter outlines the importance of three major factors and the effects of their joint action in defining local and regional climatic features of the Romanian Carpathians: latitude and longitude, topography and the regional atmospheric circulation. The chapter summarizes the role of latitude and longitude in shaping the distribution of the direct and global solar radiation across the Romanian Carpathians and highlights the main influences of regional atmospheric circulation in defining local weather aspects and the regional climatic patterns in this mountain range. The complexities introduced by the main topographic characteristics of the underlying mountain terrain (e.g. altitude, slope aspect and angle, landforms) on climate state variables, are addressed here based on the key findings of several previously published works, focusing on local climate contrasts and climate zonation aspects within the Romanian Carpathians. A major focus is on the altitude effect, imposing the overall climatic zonation, as revealed by on the key findings of several previously published works.

Projections of Future Changes in Climate of the Romanian Carpathians

This chapter briefly presents the changes of the air temperature and precipitation amounts predicted by Regional Climate Models for the next decades over the Romanian Carpathians. The analysis refers to the IPCC Scenario A1B, and exploits the outputs of several European projects developed in the recent years. The air temperature is likely to increase in all seasons, while the precipitation amounts will generally vary with ±10 % as compared to the present climate, at different spatial rates. The most significant temperature increasing is expected to occur in summer; over most Carpathian areas, the period 2021–2050 will be 2.5–3.0 °C warmer than 1961–1990. As regards the precipitation, the winter will be sensibly drier, while increasing trends are specific to the autumn.

Observed Variability and Trends from Instrumental Records

This chapter analyses the recent climatic trends in the Romanian Carpathians, with an accent on seasonal changes. Temperature trends are increasing in winter, spring and summer, while they are completely absent in autumn, which is the single stable season from a thermal point of view. On the other hand, autumn is the only season when significant increasing trends in precipitation have been found. The average wind speed is decreasing in all seasons, confirming most of the findings regarding the general tendency in the Northern Hemisphere. Snow-related trend analysis shows general decreasing trends in mean snow depth, number of days with snow cover, number of days with snowfall, and continuous snow cover duration. The increase in temperature at most of the locations, together with the slight decrease in winter precipitation explains the reduction of the snowfall days. The number of snowfall days, snow duration and mean snow depth present strong negative correlations with the NAO index for the same period (DJF). The large-scale circulation over the North Atlantic has a considerable effect on the winter season in the Romanian Carpathians.

Changing Climate Extremes in the Last Five Decades (1961–2010)

Several indices of climate extremes – based on minimum and maximum temperature, daily precipitation and daily snow cover – were used in order to check for changes over 1961–2010. The most important changes were found in maximum and (to a lesser extent) in minimum seasonal temperature. The warming signal is well retrieved in the trends in thermal-related extreme indices. Autumn is the only stable season with respect to changes in temperature extremes. Precipitation extremes exhibit no consistent change, leading to the conclusion that the decreasing trends in the snow-related indices, especially the maximum length of snowfall spells are rather related to recent warming.