Climate change and possible impact on Arctic infrastructure

There are increased concerns related to the impact of a possible global climatic change on Arctic infrastructure. Especially important is how the climatic scenarios may change (increase) the environmental loads the structures are designed for. This may cause increased risk of damage to infrastructure and threat to human lives. In addition, future infrastructure design in the Arctic may be directly affected by climate change. In order to evaluate the impact of climatic change on Arctic infrastructure, the author is of the opinion that climate change has to be treated in a similar manner to environmental loads. This means that the climatic scenarios must have a probability of occurrence or “likelihood” connected to the prediction. In this presentation the existing engineering design procedures for Arctic infrastructure are briefly presented, and the climatic scenario input data needed for infrastructure impact studies is discussed. Permafrost, Phillips, Springman & Arenson (eds) © 2003 Swets & Zeitlinger, Lisse, ISBN 90 5809 582 7 Figure 1. Damage to structure in Pyramid, Svalbard. Climate warming or maintenance problem? In the case of foundations on permafrost, the “load” can be associated with the maximum active layer thickness (thaw depth) and maximum permafrost temperature that the foundation soils will experience during the lifetime of the structure. Based on historical meteorological records and climate change scenarios, it is possible to develop probability of occurrence for such a “load”. In this presentation the existing engineering design procedures for foundations in permafrost regions are briefly presented, and the climatic scenario input data needed for infrastructure impact studies discussed. 2 DESIGN PROCEDURES FOR FOUNDATIONS IN PERMAFROST REGIONS The strength and deformation characteristics of frozen soils are dependent on soil type, temperature, density, ice content, unfrozen water content, salinity, stress state and strain rate. Thawing of the frozen soil, or even an increase of the temperature of the frozen soil, may lead to deteriorating strength and deformation characteristics, potentially accelerated settlements and possible foundation failure. Design of foundations in permafrost regions must, therefore, always include an evaluation of the maximum active layer thickness and permafrost temperature that the foundation soils will experience during the life-time of the structure. The initial and long-term bearing capacity of the foundation can then be determined. The air thawing index (ATI) is a useful parameter to determine the “magnitude” of the thawing season and will be defined in the following as an environmental load. ATI is defined as the integral of the sinusoidal air temperature variation during one year for T 0°C (the air freezing index, AFI, is defined as the integral of the sinusoidal air temperature variation during one year for T 0°C). For design purposes, the design air thawing index is commonly defined as (Andersland & Anderson 1978, Andersland & Ladanyi 1994): – the average air thawing index for the three warmest summers in the latest 30 years of record, – the warmest summer in the latest 10 years of record if 30 years of record are not available. To give design air freezing indices with varying probability of occurrence, engineering practice in Norway (related to frost protection) is based on statistical analysis of historical meteorological data (NTNF & PRA 1976). A similar approach can be used for air thawing indices in permafrost areas, see Table 1. ATI2 is approximately equal to the 30-year mean value of the air thawing index. The average air thawing index for the three warmest summers in the latest 30 year of record usually lies somewhere between ATI20 and ATI50. The magnitude of thawing to be used in the design is dependent on the type of foundation/structure and the consequences of differential settlements or failure. For road embankments, it is common to use ATI2 to ATI10, for buildings ATI50 to ATI100, while for more sensitive structures like power plants and oil or gas pipelines, higher ATIs should be considered. For thermal analysis using advanced methods such as finite element models, the design air thawing index is usually represented by a time series or a sine curve, with a combination of an average winter (AFI2) and design summer. Maximum thaw depth and permafrost temperature is usually caused by a combination of warm winter(s) and summer(s). Combinations of warm winters (low air freezing index) and warm summers (high air thawing index) should, therefore, also be considered. 3 DESIGN PROCEDURES UNDER CLIMATE CHANGE SCENARIOS Paoli & Riseborough (1998) present a thorough investigation of climate change impact on permafrost engineering design based on a change (increase) in the average temperature. The consequences of failure and climate change sensitivity of engineering projects are evaluated through a screening process. The method provides a prototype for systematically considering the issue of climate change effects on Arctic infrastructure. Khrustalev (2000) recommends, based on observations from Yakutsk, Russia, comparison of meteorological data series before 1970 to those after 1970 to take into account recent climate change. In this approach, it is assumed that temperature variation before 1970 (1830–1970) is caused by natural factors only, while the temperature increase after 1970 can be assumed to give a linear trend that can be extrapolated into the future. An alternative approach is to use the output from general circulation models (GCMs) to construct artificial air temperature time series for given locations from 2000–2100. This data can be used to investigate how the probability of occurrence of air thawing or 462 Table 1. Design air thawing index (ATI). Magnitude Probability of occurrence Predicted number of thawing in one single year occurrences ATI2 50% 1:2 Once in 2 years ATI10 10% 1:10 Once in 10 years ATI20 5% 1:20 Once in 20 years ATI100 1% 1:100 Once in 100 years ATI1000 0.1% 1:1000 Once in 10 3 years ATI10000 0.01% 1:10000 Once in 10 4 years