Cities alter the thermal regime of urban rivers in very variable ways which are not yet deciphered for the territory of Romania. The urban heat island of Suceava city was measured in 2019 and its impact on Suceava River was assessed using hourly and daily values from a network of 12 water and air monitoring stations. In 2019, Suceava River water temperature was 11.54 °C upstream of Suceava city (Mihoveni) and 11.97 °C downstream (Tişăuţi)—a 3.7% increase in the water temperature downstream. After the stream water passes through the city, the diurnal thermal profile of Suceava River water temperature shows steeper slopes and earlier moments of the maximum and minimum temperatures than upstream because of the urban heat island. In an average day, an increase of water temperature with a maximum of 0.99 °C occurred downstream, partly explained by the 2.46 °C corresponding difference between the urban floodplain and the surrounding area. The stream water diurnal cycle has been shifted towards a variation specific to that of the local air temperature. The heat exchange between Suceava River and Suceava city is bidirectional. The stream water diurnal thermal cycle is statistically more significant downstream due to the heat transfer from the city into the river. This transfer occurs partly through urban tributaries which are 1.94 °C warmer than Suceava River upstream of Suceava city. The wavelet coherence analyses and ANCOVA (analysis of covariance) prove that there are significant (0.95 confidence level) causal relationships between the changes in Suceava River water temperature downstream and the fluctuations of the urban air temperature. The complex bidirectional heat transfer and the changes in the diurnal thermal profiles are important to be analysed in other urban systems in order to decipher in more detail the observed causal relationships.

Suceava city is a territory under the urban heat island effect that leads to warm runoffs into small urban streamwaters that are highly impacted by the thermal pollution due to a combination of the small stream discharge and important runoff from impervious urban surfaces. This research detects the frequency and specificities of temperature surges in the Suceava city metropolitan area–40 surges were certainly identified in ~2 years-long time series. We analyzed the diurnal cycles of the stream temperature and correlated the atmospheric precipitation with some heated surface runoffs that resulted in aperiodic increases in the stream temperature. The high variability of rainfalls in the urban area meant that the stream temperature surges occurred rarely in all streams during the same rainfall event, despite the small distances between the watersheds (1–5 km between adjacent water monitoring points). The surges lasted up to 10 h and had an amplitude of up to 5.2 °C; they usually lasted 3.9–5.6 h after 5.8–7.7 mm rainfalls, causing temperature peaks of 0.5–1.4 °C. Additionally, they were easier to detect in the Cetăţii Creek due to its colder-than-natural waters during the warm season—a result of important wastewater discharge. Overall, the surges occurred mostly during the warm and wet semester of the year (87.5%) and especially during the summer (50%). Because Suceava is an average Romanian city, our findings could be taken into account as relevant data at least for cities located in the Moldavian Plateau.

City of Suceava, located in the NE Region of Romania, is an attraction pole for the regional inhabitants through its commercial, academic and tourist functions. The city population increased from 114462 in 1992 to 122654 in 2018. The urban area suffered major modifications between 1990 and 2018 which transposed themselves in the values of the climatic elements.The general objective of the study consists in the evaluation of the climatogen impact of the mutations occurred in the city’s demography, in the features of the active surface between 1990 (the period which followed immediately to the communist system) and 2018.The working algorithm adopted consisted of: i) identification of modifications in the active surface structure, ii) identification of the land cover flows which determine the evolution of the artificial surfaces, iii) intersection of CORINE Land Cover sets, for the years 1990 and 2018, in ArcGis through the overlay technique, iv) obtaining a matrix of land cover categories, v) identification of the land cover flows according to the working technology implemented by the European Environment Agency, vi) highlighting the correlations between the modification of the artificial areas surfaces and the evolution of the climatic elements of Suceava’s atmosphere.Results. There were identified three types of land cover flows specific to the artificial surfaces, caused by six types of processes. The biggest share is held by LCF2 (urban residential sprawl) represented by a single type of land cover flows, urban diffuse residential sprawl (lcf22) which cumulated an area of 861.74ha (2.12% of study area total). The second category shows the intraurban space conversion, defined LCF1 (urban land management) with the presence of two types of specific processes: urban development/infilling (lcf11) with a surface of 75.82ha (0.19% of the study area) and recycling of developed urban land (lcf12) with an area of 376.88ha (0.93% of study area). In the end, there was identified a small share of conversions which show the third category LCF3 (sprawl of economic sites and infrastructures) with a total of 284.66ha (0.70% of study area) and which contains three types of processes: sprawl of industrial and commercial sites (lcf31) with 129.09ha (0.32%), sprawl of airports (lcf34) with 10.27ha (0.03%) and construction (lcf37) with 145.3ha (0.36%). In total, the anthropic space from the study area was affected by conversions on a surface of 1599.1ha (3.93% of the total study area of 40685.73ha) for period 1990-2018. Meteorological data obtained from Suceava Weather Station (1961-2018) and from the urban meteorological stations SV1 and SV2 for the interval 2009-2019 were correlated by the statistics of conversions.Conclusions. At Suceava suburban weather station temperature increased with 0,4°C in the decade 1991-2000, with 0,5°C in decade 2001-2010 and with 0,9°C more in decade 2011-2019. Only in the interval 2009-2019 with hourly data from all 3 stations, the urban-suburban thermal difference was of +1,7°C in the city's favour. If the increase of temperature from suburban is allocated to the regional heating, the urban-suburban thermal difference was attributed to the amplification of the city’s topoclimatic role per se.