Hanna M. Mäkelä

A palaeotemperature record for the Finnish Lakeland based on microdensitometric variations in tree rings

X-ray based tree-ring data of maximum latewood densities (MXD) was combined for south-eastern Finland. This data originated from subfossil and modern pine (Pinus sylvestris L.) materials comprising a continuous dendroclimatic record over the past millennium. Calibrating and verifying the MXD chronologies against the instrumental temperature data showed a promising opportunity to reconstruct warm-season (May through September) temperature variability. A new palaeotemperature record correlated statistically significantly with the long instrumental temperature records in the region and adjacent areas since the 1740s. Comparisons with tree-ring based (MXD and tree-ring width) reconstructions from northern Fennoscandia and northern Finland exhibited consistent summer temperature variations through the Medieval Climate Anomaly, Little Ice Age, and the 20th century warmth. A culmination of the LIA cooling during the early 18th century appeared consistently with the Maunder Minimum, when the solar activity was drastically reduced. A number of coolest reconstructed events between AD 1407 and 1902 were coeval to years of crop failure and famine as documented in the agro-historical chronicles. Results indicate an encouraging possibility of warm-season temperature reconstructions using middle/south boreal tree-ring archives to detail and enhance the understanding of past interactions between humans, ecosystems and the earth.

Dendroclimatic signals deduced from riparian versus upland forest interior pines in North Karelia, Finland

Radial growth of boreal tree species is only rarely studied in riparian habitats. Here we investigated chronologies of earlywood, latewood, and annual ring widths and blue intensity (BI; a surrogate to latewood density) from riparian lake shore and upland forest interior pines (Pinus sylvestris L.) growing in boreal forest in eastern Finland. Riparian and upland chronologies were compared to examine differences in the pine growth variability and growth response to climatic variation in the two habitats. It was found that the climatic variables showing statistically significant correlations with the tree-ring chronologies were related to snow conditions at the start of the growing season. Deeper snowpack led to reduced upland pine growth, possibly due to delayed snowmelt and thus postponed onset of the growing season. Warm late winters were followed by increased riparian pine growth because of earlier start of the snow-melt season and thus a lower maximum early summer lake level. Moreover, riparian pines reacted negatively to increased rainfall in June, whereas the upland pines showed a positive response. Latewood growth reacted significantly to summer temperatures. The BI chronology showed a strong correlation with warm-season temperatures, indicating an encouraging possibility of summer temperature reconstruction using middle/south boreal pine tree-ring archives.

Corrosion of Reinforcement in Existing Concrete Façades

The most common degradation mechanism causing the need to repair concrete facades in Finland, is the corrosion of reinforcement due to carbonation and the small cover depths of the reinforcement. During the last almost 20 years the repair of concrete facades and balconies has been very active and this work has produced a great deal of information about the actual condition of those repaired buildings. This active condition assessment and repair work have produced an extensive and growing information base, which can be used, for example, for anticipating the upcoming repair need of concrete structures. For this purpose the data is gathered from 947 concrete buildings, which includes the distribution of different kinds of states of damage and the interdependence between the damage and other factors. The carbonation of concrete has widely advanced in the facades made in 1970s or earlier. The corrosion of reinforcement has been possible approximately last 20–30 years in those facades. Despite insufficient cover depths of concrete and far advanced carbonation of concrete, visually seen corrosion damage are relative rare. Corrosion damage appear mostly on facades, which get more rain. In Finland those are upper parts of southern and western facades.

Hourly test reference weather data in the changing climate of Finland for building energy simulations

Dynamic building energy simulations need hourly weather data as input. The same high temporal resolution is required for assessments of future heating and cooling energy demand. The data presented in this article concern current typical values and estimated future changes in outdoor air temperature, wind speed, relative humidity and global, diffuse and normal solar radiation components. Simulated annual and seasonal delivered energy consumptions for heating of spaces, heating of ventilation supply air and cooling of spaces in the current and future climatic conditions are also presented for an example house, with district heating and a mechanical space cooling system. We provide details on how the synthetic future weather files were created and utilised as input data for dynamic building energy simulations by the IDA Indoor Climate and Energy program and also for calculations of heating and cooling degree-day sums. The information supplied here is related to the research article titled “Energy demand for the heating and cooling of residential houses in Finland in a changing climate” [1].

Oak decline as illustrated through plant-climate interactions near the northern edge of species range

This paper investigates historical growth and climate records among the oak sites representing the northern edge of species range in northernmost Europe (Finland). This is to characterize plant–climate interactions for a multitude of sites where oak decline has recently been observed and understand this most recent decline in the context of the past decline studies elsewhere. Further, our paper demonstrates the procedures the tree-ring data can be used in isolating those factors significantly contributing to decline. Our findings point towards complex tree mortality dynamics. Compared to oaks that remain healthy, the declining and dead oaks represent the trees clearly having suffered from competition and edaphic position within their site. This was indicated by their reduced growth rates and more drastic growth disturbance, with indications of reduced resilience. Growth of these trees was also deteriorated by cold soil temperatures during the dormancy in addition to summer droughts. By contrast, the growth of healthy oaks has been notably ameliorated by springtime soil warming over the past decades. The results demonstrate the climatic determinants for observed decline in the northern oak sites, which may become increasingly vulnerable to higher background tree mortality rates and die-off in response to future warming and drought, although their habitats are not normally considered water-limited.

Oak decline analyzed using intraannual radial growth indices, δ13C series and climate data from a rural hemiboreal landscape in southwesternmost Finland

Decline of pedunculate oak (Quercus robur L.) was studied in SW Finland. This is a region where the species is growing near its northern distributional limit globally and a recent decline of mature trees has been described regionally. Tree rings of declining oaks were compared to the chronologies of healthy and oaks that died, climate series and stable isotope discrimination of carbon (δ13C) of comparable mature trees. The radial growth (earlywood, latewood, and annual ring width) of declining oaks was clearly deteriorated in comparison to healthy oaks, but recuperated, compared to oaks that died, through all index types. Comparison of climate relationships between growth and δ13C, expected to reflect oaks’ intrinsic water use efficiency, indicated enhancing resistance to droughts through the growing season. The growth and the climatic growth response was differentiated in declining oaks as compared with the healthy and oaks that died revealing that: (1) declining oaks exhibited decreasing competitive strength as indicated by reduced overall growth relative to healthy oaks, (2) the growth of declining oaks was more sensitive to winter conditions, but less restricted by summer droughts than the growth of other oaks, and (3) healthy oaks were seen having benefitted from the ongoing lengthening of the growing season. Lack of correlativity between growth and δ13C became evident as their responses to temperature and precipitation variations deviated drastically during the other but summer months. Our results indicate that several different ecological factors, rather than a single climatic factor (e.g., drought), are controlling the oak decline in the studied environment.

Volcanic dust veils from sixth century tree-ring isotopes linked to reduced irradiance, primary production and human health

The large volcanic eruptions of AD 536 and 540 led to climate cooling and contributed to hardships of Late Antiquity societies throughout Eurasia, and triggered a major environmental event in the historical Roman Empire. Our set of stable carbon isotope records from subfossil tree rings demonstrates a strong negative excursion in AD 536 and 541–544. Modern data from these sites show that carbon isotope variations are driven by solar radiation. A model based on sixth century isotopes reconstruct an irradiance anomaly for AD 536 and 541–544 of nearly three standard deviations below the mean value based on modern data. This anomaly can be explained by a volcanic dust veil reducing solar radiation and thus primary production threatening food security over a multitude of years. We offer a hypothesis that persistently low irradiance contributed to remarkably simultaneous outbreaks of famine and Justinianic plague in the eastern Roman Empire with adverse effects on crop production and photosynthesis of the vitamin D in human skin and thus, collectively, human health. Our results provide a hitherto unstudied proxy for exploring the mechanisms of ‘volcanic summers’ to demonstrate the post-eruption deficiencies in sunlight and to explain the human consequences during such calamity years.