Bio-Physical Proxy Data
Proxy data refers to biophysical temperature indicators in the natural environment, e.g. the developmental stages of plants (biological temperature indicators) or the duration of snow cover and the icing of rivers and lakes (physical temperature indicators).
In his "Verzeichniss über das [jeweilige] Jahr", the baker Hans Rudolf Rieter (1665-1748) recorded the course of the weather in Winterthur (Zurich) from 1721 to 1738 around the clock, often even at night. As far as we know today, he was the first person to systematically record the timing of a large number of phenological phases, such as the first cherry blossoms, the "first grapes" (budding or when the inflorescences become visible), the beginning greening of the beech trees, the full bloom of the cherry trees, the full bloom of the pear trees, the first ears of barley, the first ears of rye, the first ears of spelt, the full bloom of the rye, the full bloom of the "Korn" (grain), the beginning of the flowering of the vines, the first ripe strawberries, the first ripe cherries, the beginning of the barley harvest, the beginning of the rye harvest, the beginning of the "Korn" (grain) harvest, the end of the grain harvest, the beginning of the red colouring of the grapes and the beginning of the grape harvest. Rieter cultivated his own vineyard and, as "Rechenherr", was responsible for the financial administration and flood protection in Winterthur (Pfister 1984: 38). Only some of his phenological observations have so far been included in Euro-Climhist.
The Bernese priest Johann Jakob Sprüngli (1717-1803) was one of the most important Swiss weather observers of his time. In 1757 he was given the parish of Zweisimmen in the Bernese Oberland. In 1766 he was transferred to Gurzelen near Thun at the foot of the Stockhorn mountain range, and finally to Sutz on Lake Biel in 1784. Sprüngli's observations reveal a mania for describing the weather as comprehensively as possible and documenting it with instrumental measurements. In winter, he recorded in detail the build-up and breakdown of the snow cover in his neighbourhood and in the summer half-year he followed the snowing and thawing process on the nearby mountain ranges. He tells us the flowering time of around 100 different flowers in the garden and fields, of nine different types of fruit trees and the most important phenological phases of the different types of grain and vines. He also observed the first appearance of 39 different animal species each spring (Pfister 1984; Burri, Zenhäusern 2009). In Gurzelen, Sprüngli recorded the following garden and field work, among other things: "the first hay is planted - peas are planted - potatoes are planted early - the first sheaf of grain is planted - the first time grass is planted" (translated from German).
Johann Ignaz Inderschmitten (1743-1816), a mountain farmer in the village of Binn (canton of Valais) at an altitude of 1400 metres, served as a bailiff in the Upper Valais valley of the same name. He describes the weather and its influence on agriculture and alpine farming from 1770 to 1812 in great detail, for example the time when goats began grazing and travelling to the alpine pastures, the time of the rye harvest, the effect of heavy frosts and the duration of alpine pasture use (Zenhäusern 2008).
Christian Röthlisberger (born 1944) has been fascinated by weather and plant observations since he was at grammar school. During his work as a general practitioner in the Bernese municipality of Grossaffoltern from 1977 to 2010 and since his retirement, he has systematically carried out meteorological measurements and holistic weather observations in this area outside the official measurement networks, as we know them from the historical past. In particular, he meticulously tracks and records the development of a constantly growing number of cultivated and useful plants, including those that are missing from the MeteoSwiss phenological network but were observed in the past. In this way, it creates a phenological link between past and present, in which the increasing global warming is documented. For the time being, two of his series (the beginning of beech leaf unfolding, the beginning of wheat flowering) are included in Euro-Climhist.
Before the early 19th century, grain was cut with a sickle, then with scythes and finally with mowers during the yellow ripening period. The time of yellow ripening depends on the temperature in the period from March to July (Wetter, Pfister 2011). Since the introduction of combine harvesters around 1970, the later onset of dead maturity (when the grains fall easily from the ears) has been decisive for the time of harvest.
In the weekly issue book of Basel Hospital, the wages paid to day labourers for agricultural work were recorded daily from 1454 to 1705. This allows indirect conclusions to be drawn about the temperature conditions from March to July.
The entry shown here for the year 1522 reads: "Item Friday after Margarete [28 July according to the Gregorian calendar] in the harvest rewarded" (translated from German). According to today's calendar, the rye harvest in Basel began on 28 July that year, ten days after the long-term average harvest date of 1454-1970, which indicates cool temperatures in the period from March to July 1522. Data in narrative sources confirm this finding.
For the period from 1706 to the early 19th century, the date of the start of the harvest can also be derived from the date on which the grain tithes were auctioned. All farmers in a parish had to start harvesting their grain on the same day, partly to prevent fraud in the payment of the tithe as far as possible. The tithes were auctioned off among the wealthy farmers in the village. The successful bidder collected the agreed amount of grain and delivered it to the tithe barn. He received the resulting straw as payment. The date of the auction is recorded from the late 16th century onwards in the so-called "Zehntrödeln" (registers of tithe awards and tithe income). In the early 19th century, tithing was abolished. Until the middle of the 20th century, the harvest date can also be inferred from records kept by farmers and weather observers, and subsequently from observations made as part of the MeteoSwiss phenological network.
The beginning of the wheat harvest in what is now the Czech Republic has been known since 1501. Euro-Climhist contains a long series dating from 1501 to 2008 as part of a co-operation (Možný et al. 2012).
The date of the grape harvest depends mainly on the average temperature between April and July, and in late years on those in August. In the Swiss Plateau, it has been known continuously since 1501 (Wetter et al. 2013). Records of the start of the grape harvest are linked to the abolition of the so-called grape harvest ban, which was already practised in Roman times. When the grapes had ripened, the vineyards were banned, i.e. guarded day and night, to prevent the theft of grapes and premature harvesting at the expense of the vineyard owners. The decision was communicated to the authorised users in good time so that they could monitor the harvest. The harvest ban was cancelled by the municipal authorities. The corresponding file notes therefore form an indirect source for climate reconstruction.
The longest series of grape harvest data in Euro-Climhist is that from the French wine metropolis of Beaune in Burgundy, which dates back to 1354 (Labbé et al. 2019). In the Swiss Plateau, the corresponding data on grape harvests begin in 1444/1458 (Wetter, Pfister 2013) and for the wine-growing regions in what is now the Czech Republic, the start of the grape harvest is known from 1499 (Možný et al. 2016).
In severe winters, the lakes in the Swiss Alpine foothills freeze over in a certain order according to their surface area, depth and individual characteristics, with shallow lakes (Lake Constance/Lake Untersee, Lake Murten, Lake Biel) always freezing over before the deeper ones (Lake Zug, Lake Zurich, Lake Constance/Lake Obersee, Lake Neuchâtel, Lake Thun). There is no evidence of complete ice cover on Lake Lucerne, Lake Brienz, Lake Walen or Lake Geneva since 1501 (Pfister 1984). Smaller lakes still froze over frequently in the warm 20th century (Hendricks-Franssen, Scherrer 2008).
After the extremely cold November 1879 and the bitterly cold December 1879, the coldest since 1755, the ice on Lake Zurich became stable on 23 January 1880. A "Seegfrörni" was always an invitation to a public festival. Young and old frolicked on the ice on skates or sledges. At that time, Lake Neuchâtel, Lake Constance and large parts of Lake Lucerne and Lake Geneva at the outflow of the Rhone were also completely frozen over. After that of 1830, the winter of 1880 was the coldest since 1755 (Pfister 1999: 103).
For regions outside the Alps, reports of freezing lakes, rivers, canals or the sea are also an important climate indicator. For the Dutch city of Haarlem, a series has already been recorded from the winter of 1578/1579, which extends to 1839 and shows the number of days on which the canals in and around the city were frozen. In the future, data will be available for the Baltic region on when the ice had thawed sufficiently in spring to make the harbours navigable again.