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Longwave radiation (LR) is one of the energy balance components responsible for warming and cooling water during hot summers. Both downward incoming LR, emitted by the atmosphere, and outgoing LR emitted by the land surface are not widely measured. The influence of clouds on the LR heat budget makes it even harder to establish reliable formulations for all-sky conditions. This paper uses air temperature and cloud cover from the ERA5 reanalysis database to compare 20 models for the downward longwave irradiance (DLI) at Earth's surface and compare them with ERA5's DLI product. Our work uses long-time continuous DLI measured data at three stations over Canada, and ERA5 reanalysis, a reliable source for data-scarce regions, such as central British Columbia (Canada). The results show the feasibility of the local calibration of different formulations using ERA5 reanalysis data for all-sky conditions with RMSE metrics ranging from 37.1 to 267.3 W m−2, which is comparable with ERA5 reanalysis data and can easily be applied at broader scales by implementing it into hydrological models. Moreover, it is shown that ERA5 gridded data for DLI shows the best results with RMSE = 31.7 W m−2. This higher performance suggests using ERA5 data directly as input data for hydrological and ecological models. [ABSTRACT FROM AUTHOR]

Air temperature (Ta) is an important climatological variable for forest research and management. Due to the low density and uneven distribution of weather stations, traditional ground-based observations cannot accurately capture the spatial distribution ofTa, especially in mountainous areas with complex terrain and high local variability. In this paper, the daily maximumTain British Columbia, Canada was estimated by satellite remote sensing. Aqua MODIS (Moderate Resolution Imaging Spectroradiometer) data and meteorological data for the summer period (June to August) from 2003 to 2012 were collected to estimateTa. Nine environmental variables (land surface temperature (LST), normalized difference vegetation index (NDVI), modified normalized difference water index (MNDWI), latitude, longitude, distance to ocean, altitude, albedo, and solar radiation) were selected as predictors. Analysis of the relationship between observedTaand spatially averaged remotely sensed LST indicated that 7 × 7 pixel size was the optimal window size for statistical models estimatingTafrom MODIS data. Two statistical methods (linear regression and random forest) were used to estimate maximumTa, and their performances were validated with station-by-station cross-validation. Results indicated that the random forest model achieved better accuracy (mean absolute error, MAE = 2.02°C,R2 = 0.74) than the linear regression model (MAE = 2.41°C,R2 = 0.64). Based on the random forest model at 7 × 7 pixel size, daily maximumTaat a resolution of 1 km in British Columbia in the summer of 2003–2012 was derived, and the spatial distribution of summerTain this area was discussed. The satisfactory results suggest that this modelling approach is appropriate for estimating air temperature in mountainous regions with complex terrain. [ABSTRACT FROM AUTHOR]

Direct observations of urban surface temperature in daytime are made using a thermal scanner mounted in a helicopter over three land-use areas in Vancouver, B.C. The results reveal strong directional variations in the observed apparent surface temperature. The variations arise due to the differential patterns of irradiated and shaded surfaces within the sensor field of view created by the three-dimensional urban surface structure and the position of the Sun. The directional variations may be considered to be a form of effective anisotropy due to the large scale roughness of the urban surface. Variations in excess of 9 C were measured over a downtown area. Urban residential and light industrial land-use areas also exhibited strong effective anisotropy. The directional temperature variations are of similar magnitude to atmospheric corrections applied to thermal imagery. This implies that effective anisotropy should receive serious consideration in the interpretation of thermal imagery obtained over urban areas. The scale dependence of the effective anisotropy is discussed. [ABSTRACT FROM AUTHOR]

• Elevated air temperature in combination with higher VPD causes changed terpenoid contents and emissions in Douglas fir. • Such responses were provenance-specific. • Decreased terpenoid contents might weaken defense against herbivores causing higher susceptibility of the provenance affected. In the present work, we studied the effects of elevated air temperatures, which were above the optimum for photosynthesis, in combination with enhanced atmospheric VPD on two Douglas fir provenances grown under controlled conditions in a climate chamber. Provenance Monte Creek (MC) from the menziesii-glauca transition zone, Southern British Columbia, Canada, was derived from a dry environment receiving ca. half of the precipitation at its natural site than the interior provenance Pend Oreille (PO) from a mesic site in Northeast Washington State, US. We determined the terpenoid contents in needles and roots of the trees as well as terpene emission from needles and terpenoid synthase activities observing clear provenance-specific patterns. Whereas total terpenoid contents in needles dropped significantly in provenance PO in response to thermal stress, they remained unaffected in MC. The drop in terpenoid content in PO was due to decreased abundance of almost all identified terpenoids with exception of five compounds. Terpene emission was significantly enhanced in thermal-stressed provenance MC but it was unaffected in provenance PO. Oppositely, root terpenoid contents were rather stable in both provenances upon high temperature and enhanced atmospheric VPD. Similarly, we did not observe stress effects on terpenoid synthase activity, which was used as a proxy for the formation of terpenoids. The results indicate that features of the original habitat of the trees determine plant chemotypic properties, for example, thermal stress related responses. The observed decrease of terpenoid levels in needles of PO after long-term exposure to elevated temperature/enhanced atmospheric VPD, might weaken stress-exposed trees. Since terpenoids are essential components of the conifers' defense arsenal against herbivores, decreased terpenoid levels might increase susceptibility of stressed trees to above- and belowground herbivore challenges. [ABSTRACT FROM AUTHOR]