Midwinter Months Research Articles

The MOSAiC Distributed Network: Observing the coupled Arctic system with multidisciplinary, coordinated platforms

Central Arctic properties and processes are important to the regional and global coupled climate system. The Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) Distributed Network (DN) of autonomous ice-tethered systems aimed to bridge gaps in our understanding of temporal and spatial scales, in particular with respect to the resolution of Earth system models. By characterizing variability around local measurements made at a Central Observatory, the DN covers both the coupled system interactions involving the ocean-ice-atmosphere interfaces as well as three-dimensional processes in the ocean, sea ice, and atmosphere. The more than 200 autonomous instruments (“buoys”) were of varying complexity and set up at different sites mostly within 50 km of the Central Observatory. During an exemplary midwinter month, the DN observations captured the spatial variability of atmospheric processes on sub-monthly time scales, but less so for monthly means. They show significant variability in snow depth and ice thickness, and provide a temporally and spatially resolved characterization of ice motion and deformation, showing coherency at the DN scale but less at smaller spatial scales. Ocean data show the background gradient across the DN as well as spatially dependent time variability due to local mixed layer sub-mesoscale and mesoscale processes, influenced by a variable ice cover. The second case (May–June 2020) illustrates the utility of the DN during the absence of manually obtained data by providing continuity of physical and biological observations during this key transitional period. We show examples of synergies between the extensive MOSAiC remote sensing observations and numerical modeling, such as estimating the skill of ice drift forecasts and evaluating coupled system modeling. The MOSAiC DN has been proven to enable analysis of local to mesoscale processes in the coupled atmosphere-ice-ocean system and has the potential to improve model parameterizations of important, unresolved processes in the future.

Cool season precipitation projections for California and the Western United States in NA-CORDEX models

Understanding future precipitation changes is critical for water supply and flood risk applications in the western United States. The North American COordinated Regional Downscaling EXperiment (NA-CORDEX) matrix of global and regional climate models at multiple resolutions (~ 50-km and 25-km grid spacings) is used to evaluate mean monthly precipitation, extreme daily precipitation, and snow water equivalent (SWE) over the western United States, with a sub-regional focus on California. Results indicate significant model spread in mean monthly precipitation in several key water-sensitive areas in both historical and future projections, but suggest model agreement on increasing daily extreme precipitation magnitudes, decreasing seasonal snowpack, and a shortening of the wet season in California in particular. While the beginning and end of the California cool season are projected to dry according to most models, the core of the cool season (December, January, February) shows an overall wetter projected change pattern. Daily cool-season precipitation extremes generally increase for most models, particularly in California in the mid-winter months. Finally, a marked projected decrease in future seasonal SWE is found across all models, accompanied by earlier dates of maximum seasonal SWE, and thus a shortening of the period of snow cover as well. Results are discussed in the context of how the diverse model membership and variable resolutions offered by the NA-CORDEX ensemble can be best leveraged by stakeholders faced with future water planning challenges.

Changes in the zonal mean flow, temperature, and planetary waves observed in the Northern Hemisphere mid-winter months during the last decades

Four sets of data: the UK Met Office, Modern Era Retrospective-analysis for Research and Applications (MERRA), Japanese 55-year Reanalysis data (JRA-55), and ERA-Interim data (ERA) have been used to estimate the climatic variability of the zonal mean flow, temperature, and Stationary Planetary Waves (SPW1, SPW2) from the troposphere up to the lower mesosphere levels. The composites of the meteorological fields during mid-winter month have been averaged over the first (1995–2005) and second (2006–2016) 11 years intervals and have been compared mainly paying attention to interannual and intraseasonal variability. Results show that changes in the mean fields and SPW2 are weaker and statistical significance of these changes is lower in comparison with the changes observed in the intraseasonal variability of these characteristics. All data sets demonstrate a decrease of SPW1 amplitude at the higher-middle latitudes in the lower stratosphere and opposite effect in the upper stratosphere. However, there is an increase of the intraseasonal variability for all meteorological parameters and this rise is statistically significant. The results obtained show that UK Met Office data demonstrate stronger changes and increase of the intraseasonal variability in comparison with other data sets.

Elevated chaperone proteins are a feature of winter freeze avoidance by larvae of the goldenrod gall moth, Epiblema scudderiana

Winter survival for many insect species includes a need to maintain metabolic homeostasis and structural/functional integrity of macromolecules not only over a wide range of cold temperatures but also in response to rapid temperature change. Chaperones are well-known to protect/stabilize protein structure with regard to heat stress but less is known about their potential involvement in long-term protection of the proteome at subzero temperatures. The present study assessed the participation of chaperone proteins in the cold hardiness of larvae of the goldenrod gall moth, Epiblema scudderiana (Clemens) (Lepidoptera, Olethreutidae), monitoring changes in nine proteins over the winter months as well as their responses to laboratory cold acclimation or anoxia exposure. Four heat shock proteins (HSPs: Hsp110, Hsp70, Hsp60, Hsp40), three glucose-regulated proteins (GRPs: Grp78, Grp 94, Grp170) and the tailless complex polypeptide 1 (TCP-1) as well as the heat shock transcription factor (HSF1) were investigated. In general, all were significantly elevated in larvae collected from an outdoor site between October and March, as compared with September values, and chaperone levels were reduced again in April. The October to March interval also includes the period of diapause followed by cold quiescence in the species. Relative expression of Hsp70, Hsp60 and Hsp40 rose by 2–3-fold, GRPs increased 1.5–3-fold, and levels of active (hyperphosphorylated) HSF1 increased by 4–4.8-fold over the midwinter months. Chilling from 15°C to 4°C in the laboratory upregulated Grp78 protein content that remained high as temperature was further reduced to −4°C and then −20°C whereas Hsp110, Hsp70 and HSF1 levels increased when larvae were exposed to −4°C and −20°C. Grp170 (also known as oxygen-regulated protein 150) was the only chaperone that increased significantly in the larvae in response to anoxia exposure at 4°C. The data also indicated that multiple subcellular compartments received enhanced protection for their proteome since upregulation of chaperones included proteins known to occur in cytosolic (Hsp40, Hsp70), mitochondrial (Hsp60) and endoplasmic reticulum (Grp170) locations. Overall, the data indicate that chaperones have a significant role to play in the winter cold hardiness of E. scudderiana and identify declining temperatures (and perhaps also oxygen restriction) as potential modulators of chaperone production. The data add support to a relatively understudied area of insect cold hardiness – the long-term protection and stabilization of the proteome over the winter months.

Temporal dynamics of Puumala hantavirus infection in cyclic populations of bank voles

Understanding the dynamics of zoonotic pathogens in their reservoir host populations is a prerequisite for predicting and preventing human disease epidemics. The human infection risk of Puumala hantavirus (PUUV) is highest in northern Europe, where populations of the rodent host (bank vole, Myodes glareolus) undergo cyclic fluctuations. We conducted a 7-year capture-mark-recapture study to monitor seasonal and multiannual patterns of the PUUV infection rate in bank vole populations exhibiting a 3-year density cycle. Infected bank voles were most abundant in mid-winter months during years of increasing or peak host density. Prevalence of PUUV infection in bank voles exhibited a regular, seasonal pattern reflecting the annual population turnover and accumulation of infections within each year cohort. In autumn, the PUUV transmission rate tracked increasing host abundance, suggesting a density-dependent transmission. However, prevalence of PUUV infection was similar during the increase and peak years of the density cycle despite a twofold difference in host density. This may result from the high proportion of individuals carrying maternal antibodies constraining transmission during the cycle peak years. Our exceptionally intensive and long-term dataset provides a solid basis on which to develop models to predict the dynamic public health threat posed by PUUV in northern Europe.

Human rhino- and enteroviruses in children with respiratory symptoms in Luanda, Angola

Objectives:The role of human rhinoviruses (HRV) and human enteroviruses (HEV) in common colds, as well as their seasonality, remains largely unknown in tropical environments. The study aimed to define the frequency and clinical features of HRV and HEV in children with respiratory symptoms in tropical Africa during autumn and winter.Methods:Clinical data and PCR assays of nasopharyngeal swabs (NPS) were collected from 67 (66%) children with and 35 (34%) children without chronic illnesses who were attending different outpatient clinics at a paediatric tertiary-care hospital in Luanda, Angola.Results:Thirty-six (35%) children had HIV infection, and 27 (26%) were malnourished. Thirty-seven (36%) out of 102 NPS specimens were virus-positive: 34 (33%) for HRV and 10 (10%) for HEV. Seven (7%) had co-infection. The highest HRV-positivity rate (47%) occurred in July (P = 0·02), a mid-winter month with high relative humidity but no precipitation. Virus positivity was associated with younger age (median 36 vs 52 months, P = 0·02) but not with specific symptoms or findings.Conclusions:HRVs play a major role in young children’s respiratory infections in urban tropical Angola during autumn and winter. A better understanding is required of the seasonality and clinical outcomes of these viruses in children living in resource-poor tropical countries.

Seasonal variation in boreal pine forest albedo and effects of canopy snow on forest reflectance

The low shortwave albedo of evergreen coniferous forests increases net radiation and thus the local temperature as compared to open areas. The difference between albedos of evergreen forests and open areas is most pronounced in winter and spring, when the forest canopies mask the reflective ground snow. However, also the albedo of coniferous evergreen forests changes as a function of the amount and optical properties of snow in the ground and canopy. In this study, we examined the shortwave radiation balance of a boreal Scots pine dominated forest. Canopy snow cover was observed to substantially influence the albedo, increasing it by about 0.2 as compared to snow free conditions. However, albedo varied greatly between and within the canopy snow classes, probably due to differences in illumination conditions and snow amount and properties. During midwinter months, most of the incident solar radiation was reflected during days with a lot of snow in the canopy. The difference in reflected radiation between the winters with least and most snow was 54MJm−2, which was also close to the difference (55MJm−2) between the reflectance of an average winter and that of a simulated snow free winter, corresponding to less than 2% of the annual solar irradiance. The albedo of the forest was greatest in midwinter, when the cold weather and low solar radiation caused the falling snow to remain on the tree branches. As the incident solar radiation in these months is very low, we concluded that the positive feedback to climate warming in case of a potentially decreased snow cover in this boreal pine forest would remain small.

Is Pacific Storm-Track Activity Correlated with the Strength of Upstream Wave Seeding?

Abstract In this paper, the relationship between upstream seeding over north Asia and downstream storm-track activity over the North Pacific in midwinter and spring/fall has been analyzed using 45 years of variance and feature-tracking statistics. It is shown that for each season, interannual variations in upstream seeding and downstream storm-track activity are largely uncorrelated. Moreover, during midwinter months in which the upstream seeding from north Asia is about as strong as that during a typical spring/fall month, the downstream storm track in central Pacific is still significantly weaker during midwinter than that during spring/fall. In addition, during cool seasons in which the midwinter suppression is more pronounced in the upstream seeding region, the suppression is not significantly enhanced in the downstream Pacific storm track. A recent study suggested that reduced upstream seeding from north Asia is the main “source” of the midwinter suppression of the Pacific storm track. Results presented in this study suggest that it is unlikely that the weakness in upstream seeding is the primary cause of the midwinter suppression.

Meteorological factors affecting the speed of movement and related impacts of extratropical cyclones along the U.S. east coast

The speeds of historical cool-season extratropical cyclones along the U.S. east coast, hereafter East Coast Winter Storms (ECWS), occurring during the period from 1951 to 2006 were computed. Average storm speed was 13.8 ms−1 with stronger storms generally moving faster than weaker storms and faster storms forming during the midwinter months (December–March). There was no clear trend in ECWS speed during the time period, although considerable season-to-season variability was present. The monthly and seasonal variations in storm speed could not be attributed to the El Nino-Southern Oscillation or North Atlantic Oscillation (NAO) alone. However, the speed of ECWS was considerably slower when both El Nino and the negative phase of NAO occurred simultaneously. Characteristic patterns in the upper levels of the atmosphere, specifically 300 hPa zonal winds and 500 hPa geopotential heights, were present during periods when ECWS speeds were among the slowest (and separately fastest). For slow storm speed, these patterns also prevailed during months in which El Nino and negative NAO phase occurred. These patterns were also present during months with extended runs of high oceanic storm surge. This provides a qualitative link between the atmospheric conditions associated with slow storms and potentially high coastal storm surge impacts. Among the prime consequences of ECWS speed are extended periods of high storm surge, mainly due to slow-moving storms. The sustained high tidal levels often lead to substantial damage caused by coastal flooding, overwash, and beach erosion.

Comments on “The Source of the Midwinter Suppression in Storminess over the North Pacific”

In a recent paper, Penny et al. employed feature tracking to investigate why there is a relative minimum in storminess during winter within the Pacific storm track. They concluded that reduced upstream seeding, especially seeding from northern Asia, is the main “source” of the midwinter suppression of the Pacific storm track. Results presented here show that during midwinter months when upstream seeding is as strong as that in spring/fall, the Pacific storm track is not significantly stronger than average and is still much weaker than that in spring/fall, suggesting that the strength of upstream seeding cannot be the primary cause of the midwinter suppression of Pacific storm-track activity.

Winter Longitudinal Thermal Regime in Four Mountain Streams

We measured winter thermal characteristics longitudinally in four third-order streams, two each in the Idaho Batholith and Blue Mountain ecoregions. From November to April we measured temperature along 3.7 km to 11.9 km of stream at six to eight sites. Streams were snow covered for most of the winter. There was a seasonal pattern of stream-wide cooling in November and warming in April at all streams. In the mid-winter months (December, January, and February), the sites in the Blue Mountain streams had mean monthly maxima ranging from 0.2 to 3.0 °C and minima -0.1 to 1.5 °C stream-wide, whereas both Idaho Batholith streams were near 0.0 °C throughout their length and had monthly ranges of 0.2 °C or less. Winter temperature differences between streams of the two ecoregions create substantial differences in cumulative degree-days which could be a factor in the structure of instream biotic communities.

Changes in abundance of heterotrophic and coliform bacteria resident in stored water bodies in relation to incoming bacterial loads following rain events

Microbial properties of harvested rainwater were assessed at two study sites at Newcastle on the east coast of Australia. The investigation monitored daily counts of heterotrophic bacteria (HPC), total coliforms and E. coli during a mid-winter month (July). Immediately after a major rainfall event, increases in bacterial loads were observed at both sites, followed by gradual reductions in numbers to prior baseline levels within 7 days. Baseline HPC levels ranged from 500-1000 cfu/mL for the sites evaluated, and the loads following rain peaked at 3590-6690 cfu/mL. Baseline levels of total coliforms ranged from 0-100 cfu/100 mL and peaked at 480-1200 cfu/100 mL following rain. At Site 1, there was no evidence of E. coli loading associated with the rain events assessed, and Site 2 had no detectable E.coli colonies at baseline, with a peak load of 17 cfu/100 mL following rain which again diminished to baseline levels. It was concluded that rainfall events contributed to the bacterial load in rainwater storage systems, but processes within the rainwater storage ensured these incoming loads were not sustained.

Relationship between climate change and vegetation distribution in the Mediterranean mountains: Manzanares Head valley, Sierra De Guadarrama (Central Spain)

This work analyzes the consequences of climate change in the distribution of the Mediterranean high-mountain vegetation. A study area was chosen at the Sierra de Guadarrama, in the center of the Iberian Peninsula (1,795 to 2,374 m asl). Climate change was analyzed from the record of 18 variables regarding temperature, rainfall and snowfall over the period 1951–2000. The permanence of snow cover (1996–2004), landforms stability and vegetation distribution in 5 years (1956, 1972, 1984, 1991 and 1998) were all analyzed. The Nival Correlation Level of the different vegetation classes was determined through their spatial and/or temporal relationship with several climatologic variables, snow cover duration and landforms. In order to quantify trends and major change processes, areas and percent changes were calculated, as well as Mean Annual Transformation Indices and Transition Matrices. The findings reveal that in the first part of the study period (up to the first half of the 1970s) the temperature rise in the mid-winter months caused the reduction of some classes of nival vegetation, while others expanded, favored by high rainfall, decrease in both maximum temperatures and summer aridity, and longer snow cover duration. The second part of the study period was characterized by the consolidation of the increase in all thermal variables, along with an important reduction in rainfall volume and snow cover duration. As a result, herbaceous plants, which are highly correlated with a long snow permanence and abundance of melting water, have been replaced by leguminous shrubs which grow away from the influence of snow, and which are steadily becoming denser.

Evaluating the performance of the MODIS Leaf Area Index (LAI) product over a Mediterranean dryland planted forest

The launch of the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Terra and Aqua satellites improved the ability to evaluate several surface biophysical parameters, including Leaf Area Index (LAI), which is provided as an operational MODIS product, available at 1-km spatial resolution and at 8-day intervals. However, for heterogeneous and sparse planted forests that are common to the semi-arid eastern Mediterranean region, the data at low spatial resolution may be significantly biased by the contribution of different background elements to the total surface reflectance received by the sensor and cannot therefore correctly reflect the real forest phenology. In the current paper the performance of the MODIS LAI product was examined over a dryland Mediterranean forest in southern Israel. The study found a significant discrepancy between ground-based and MODIS LAI datasets. In general, MODIS LAI values were c.51% of the ground-based LAI measurements. In addition ground based LAI peaked in the summer due to the natural growth cycle of the pine trees, while MODIS values peaked in the winter. The MODIS seasonal course could be explained by the development of annuals and crypto- and micro-phytes in the understorey and the clearing areas during the mid winter months that are included in the MODIS LAI product but not in the ground based measurements. However, for that period MODIS estimates should have exceeded ground-based estimates while in fact they were still lower. The relationship between MOD12C1 Land Cover Type 3 and MOD15A2 products is discussed.

Large blackouts in North America: Historical trends and policy implications

Using data from the North American Electric Reliability Council (NERC) for 1984–2006, we find several trends. We find that the frequency of large blackouts in the United States has not decreased over time, that there is a statistically significant increase in blackout frequency during peak hours of the day and during late summer and mid-winter months (although non-storm-related risk is nearly constant through the year) and that there is strong statistical support for the previously observed power-law statistical relationship between blackout size and frequency. We do not find that blackout sizes and blackout durations are significantly correlated. These trends hold even after controlling for increasing demand and population and after eliminating small events, for which the data may be skewed by spotty reporting. Trends in blackout occurrences, such as those observed in the North American data, have important implications for those who make investment and policy decisions in the electricity industry. We provide a number of examples that illustrate how these trends can inform benefit-cost analysis calculations. Also, following procedures used in natural disaster planning we use the observed statistical trends to calculate the size of the 100-year blackout, which for North America is 186,000 MW.

Asymmetry in the interhemispheric planetary wave-tide link between the two hemispheres

This study assesses the relation between the year-to-year variability of the semidiurnal tides (SDT) observed at high latitudes of both hemispheres and the global stratospheric stationary planetary wave (SPW) with zonal wavenumber S=1 (SPW1) derived from the UKMO temperature data. No significant positive correlation can be identified between the interannual variability of the Northern Hemisphere (NH) SDT and the Southern Hemisphere (SH) SPW1 for austral late-winter months. In contrast, a good consistency is evident for the interannual variations between the SDT observed at Rothera (68°S, 68°W) and the Arctic SPW1 for NH mid-winter months. Since it has been observed that during austral summer the non-migrating SDT often plays a significant role at the latitude of Rothera, a physical link between the SH SDT and the NH SPW is suggested. This asymmetry in the interhemispheric link is also noted in a recent study.

Potential effects of climate change on the growth of lodgepole pine across diameter size classes and ecological regions

We examined 65 lodgepole pine ( Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) sites in Alberta using a dendrochronological approach in order to examine the relationships between climate and growth of lodgepole pine across elevational ecoregions and diameter size classes. The 4 elevational ecoregions sampled included the Boreal Highlands (BH: 13 sites); the Foothills (FH: 36 sites); a grouping of the montane and subalpine zones of the southern Rocky Mountains (RM: 12 sites); and the montane zone of the Cypress Hills (CH: 4 sites). The first diameter size class was comprised of the three largest (top) diameter trees at each site. The tree list of each plot was ranked, then divided into three groups of equal basal area and the tree at the midpoint of each group (small, medium, and large) was selected for the other three size classes. Annual growth in basal area of lodgepole pine was generally sensitive to heat and moisture stress in late summer of the previous year, the degree of winter harshness, and the timing of the start of the growing season. Growth was inhibited by low temperature in all winter months at the most northern BH sites which had the coldest winters, but this effect was interrupted in some of the midwinter months in the more southerly sites in the RM, and we postulated this was due to the damaging influences of Chinook winds. Interannual growth patterns were strongly correlated between top diameter trees and the other classes, and trees of all diameter classes generally responded to climate in the same way, which indicated that it is sufficient to sample only the largest diameter trees in a stand to provide insight into growth–climate relationships. The forecasted growth estimates indicate that future climate warming will negatively impact the productivity of lodgepole pine in the FH, the heart of lodgepole distribution and productivity in Alberta.

Epidemiological Profile and Clinical Associations of Human Bocavirus and Other Human Parvoviruses

BackgroundHuman bocavirus (HBoV) and PARV4 are newly discovered human parvoviruses. HBoV, which was first detected in respiratory samples, has a potential role in the development of human respiratory disease. The present study compared the frequencies, epidemiological profiles, and clinical backgrounds of HBoV and PARV4 infections with those of other respiratory virus infections, by evaluating diagnostic samples referred to the Specialist Virology Laboratory (SVL) at the Royal Infirmary of Edinburgh (Edinburgh, United Kingdom) MethodsAnonymized samples and study subject information were obtained from the respiratory sample archive of the SVL. Samples were screened for HBoV, PARV4, B19, respiratory syncytial virus (RSV), adenoviruses, influenza viruses, and parainfluenza viruses by use of nested polymerase chain reaction ResultsHBoV infection was detected in 47 (8.2%) of 574 study subjects,&ranking third in prevalence behind RSV infection (15.7%) and adenovirus infection (10.3%). Peak incidences of HBoV were noted among infants and young children (age, 6–24 months) during the midwinter months (December and January) and were specifically associated with lower respiratory tract infections. HBoV infections were frequently accompanied by other respiratory viruses (frequency, 43%), and they were more prevalent among individuals infected with other respiratory viruses (17%), frequently adenovirus or RSV. All respiratory samples were negative for PARV4 ConclusionsIn the present study, HBoV was a frequently detected, potential respiratory pathogen, with a prevalence and an epidemiological profile comparable to those of RSV. Identification of HBoV infections may be clinically important in the future

Regional and global atmospheric patterns governing rainfall in the southern Levant

This study attempts to find a linkage between the interannual variations of the rainfall measured in 12 stations spread over the northern half of Israel (the southern Levant) and atmospheric circulations ranging from regional to global scale. The analysis was done for the midwinter months, December–February, in which two-thirds of the annual rainfall occurs, during the years 1950–2002. The study is based on composite maps for extremely dry/wet seasons and on maps of correlation between atmospheric variables and the rainfall time series. Our results show that an upper-level trough extending from Eastern Europe toward the Eastern Mediterranean (EM) is closely linked with the seasonal rainfall over the study area. This is expressed by a correlation of −0.74 between the 500-hPa geopotential height at 32.5°N, 35°E and the rainfall. This trough has two effects on the southern Levant rainfall: one is the dynamics implied by the upper trough and the other is the cool advection over the EM imparted by the northwesterly flows induced by the trough. The latter presumably enhances the atmospheric instability when it sweeps over the warmer waters of the EM. The upper trough was found to be associated with three global factors: the polar stratospheric jets, in both the Northern and Southern Hemispheres, and the SST variations over the western tropical Pacific Ocean, represented by the ‘Pacific Warm Pool’ index. The EM trough is accompanied by a ridge covering western Europe, so that cold and wet winters in the southern Levant coincide with warm and dry winters over western Europe and vice versa. Copyright © 2005 Royal Meteorological Society.

Afforestation and stream temperature in a temperate maritime environment

There have been few long term investigations of the effects of afforestation on stream temperatures in the UK, and the present study uses the results of continuous monitoring of water temperatures in a forest and a moorland stream of the Loch Grannoch area in southwest Scotland over a 4 year period to investigate the effects of planting coniferous forest on stream thermal regime. The presence of a coniferous tree canopy resulted in a lowering of mean water temperatures by ∼0·5 °C but larger reductions in summer monthly mean maxima and diel ranges of up to 5 °C and 4 °C respectively. The diel cycle in the forested stream lagged behind that of the moorland site in all months of the year, but the delay in timing was greater for the peak than for the trough in the diel cycle. Mean water temperatures were higher in the forest stream during the mid-winter months, reflecting higher minimum values. Contrasts in stream thermal regime between forest and moorland showed relatively little interannual variability over the study period. Continuous monitoring of air temperatures during 2002 revealed contrasts between the study sites that were less pronounced for air than for water temperature, and suggested it is the shading of incoming solar radiation that has a strong effect in determining the water temperature behaviour of the forested stream. Although the biological impact of the observed contrasts in stream temperature between land uses is likely to be relatively modest, the presence of forest cover moderates the occurrence of high summer temperatures inimical to the survival of some salmonid species. Copyright © 2005 John Wiley & Sons, Ltd.