1. Historical documentary records to reconstruct climate in Norway
Elin Lundstad1*, Øyvind Nordli1 & Martin W. Miles2,3
Norwegian Meteorological Institute (met.no), Oslo, Norway 2) Bjerknes Centre for Climate Research,
Bergen, Norway 3) Environmental Systems Analysis Research Center, Boulder, Colorado, USA *
Historical documentary data provide valuable information on the paleoclimate and are useful for constructing long, high-resolution time series from historical times to the present, thereby complementing and supplementing instrumental measurements.
Both meteorological and parameteorological observations are used in the analysis presented here, based on detailed weather descriptions available from a diary series from the Åker farm in Hamar, Eastern Norway (Fig. 1), 1749 to 1835.
Temperature: The Åker temperature series is strongly correlated (rs = 0.77) to another proxy temperature dataset based on the start of the grain harvest in eastern Norway for the same period (Nordli 2001) (Fig. 3).
The Åker temperature series also correlated with a long instrumental temperature series from Uppsala, Sweden, though only moderate agreement is found, rs = 0.51.
Precipitation: The Åker series shows less precipitation in 1749 than 1835 (Fig. 4). The precipitation regime in 1749–1835 is consistent with the 20th century, although the precipitation frequency appears lower. Several severe droughts are also reported.
The climate reconstruction implies conditions consistent with the climate of the LIA. The climate in 1749–1835 was apparently both colder and wetter than today, and the year 1812 was especially cold. A notable climate anomaly in the Åker diaries is the July 1789 “Storofsen”, the biggest flood in eastern Norway in historical times.
1. Introduction
5. Results and conclusions
Abstract. Documentary descriptions of weather from a diary written in Hamar, Norway from 1749 to 1835 provide the basis to deduce some features of temperature conditions and precipitation regimes. Here an index method is developed and used to quantify these qualitative climate-proxy observations in order to reconstruct temperature, precipitation, wind and cloud-cover annually and for winter and summer. Indices are defined on the basis of the subjective evaluations of the degree of warmth and cold provided by the writer. Monthly and annual standardized anomalies are computed, enabling analysis of interannual variability of the temperature conditions. Anomalies in physical units are also estimated. The prominent fluctuations agree with those who observed in Oslo, although inconsistencies remain in specific months. The precipitation regime in is consistent with that of the 20th century, although the precipitation frequency appears lower. Several severe droughts are also reported. Despite the methodological limitations, the reconstruction appears reliable. The annual and seasonal resolution of the Aker series are found to contain the best result when the observations are based on combined data from direct weather observations and phenological information.
Fig. 3. Summer temperature index and comparison to independent temperature proxy.
The original Åker farm manuscript diaries (Fig. 2) were written by the military family Todderud over three generations. The diaries are kept at the public archives in Hamar.
An index method was developed and used to quantify these qualitative climate-proxy observations, in order to reconstruct temp-eratures and precipitation annually and for winter and summer.
Temperature: Description of the thermal state is based on Todderud’s perception and is quantified by means of an index that represents the degree of warmth or cold or specific weather conditions, similar to the approach described by Kastellet et al. (1998). The index ranges from –3 (coldest) to +3 (warmest) Coldest Warmest
Precipitation: A similar index is used, termed by little rain (drought -3) or a lot of rain (+3), including how many rainy days and how it affects growth and harvest at the farm.
Wind force and direction, cloud cover and climate anomalies are also considered here.
The reconstructed Åker series (e.g., Fig 3) are compared with other climatic time series (both proxy and instrumental) using parametric and non-parametric methods, e.g., Spearman’s rank-correlation.
3. Data sources
4. Methodology
Fig. 1 Location map of the Åker study site, located by the lake Mjøsa, Eastern Norway.
Fig. 4. Annual precipitation index.
The objectives are to:
Develop and improve methods to use these documentary records to reconstruct climate, particularly temperature and precipitation.
Reconstruct climatic conditions there from 1749–1835, a period during the last part of the so-called Little Ice Age (LIA).
Assess how well the diaries describe the late LIA weather and climate, compared with other climatic time series.
2. Objectives
Kastellet, E. et al. 1998: Geografiska Annaler. 80A, 51–65.
Nordli, P. Ø. 2001: Climatic Change 48, 201–218.
References
Fig. 2. Photo of a diary (inset) and page of text written in Gothic script.