Bio-Physical Proxy Data

Proxy data are references to bio-physical temperature indicators in the near-natural environment, such as the stages of vegetation development (biological temperature indicators) or the duration of snow cover and the freezing of lakes and rivers (physical temperature indicators).

In his “Register of the Year” the baker Hans-Rudolf Rieter (1665-1748) minuted the weather conditions between 1721 and 1738 in Winterthur (Canton Zurich) during the course of the day, to some extent even during the night (series 2). According to present knowledge he systematically recorded in this context a substantial number of phenological observations, namely the date of the first sweet cherry blossom (series 16), the first grapes (i.e. the appearance of flower heads), the unfolding of beech leaves, the full flower of sweet cherries and pears, the appearance of rye and spelt ears, the full flower of rye, spelt and vines, the first ripe strawberries and the first ripe cherries, the begin of barley, rye and spelt harvest, the end of the spelt harvest, the veraison (onset of grape ripening) and the begin of grape harvest. Rieter cultivated his own vineyard. He acted as bookkeeper in the town of Winterthur and he was also responsible for flood protection (Pfister 1984: 38). Only a part of his phenological observations has already been integrated in Euro-Climhist.

The Bernese parson Johann Jakob Sprüngli (1717-1803) needs to be mentioned among the most important Swiss weather observers of his time. In 1757 he took over responsibility for the parish of Zweisimmen in the Bernese Oberland. In 1766 he was moved to the small parish of Gurzelen near Thun (Bernese Oberland); from 1784 until his death he administered the parish of Sutz at the shore of Lake Biel. Sprüngli was committed to reporting the course of the weather in all its aspects besides making instrumental measurements. He details the formation and dissolution of snow cover in his immediate surrounding including the mountain chains in his range of vision. Moreover, he reports the blossoming and ripening time for 100 different wild and garden plants including 9 varieties of fruit trees, grape-vines and several grain varieties. Finally, he reported about the seasonal activities of 39 different wild animals (Pfister 1984; Burri, Zenhäusern 2009). In Gurzelen Sprüngli reported amongst other the time of the following gardening and field work (see document above): “start of hay harvest – tucking of peas – tucking of early potatos – start of grain (spelt) harvest – first cut of grass in spring”

Johann Ignaz Inderschmitten (1743-1816) was a mountain farmer in the village of Binn (Canton Valais) situated at 1400 a.s.l., where he acted as a court usher in the valley. He details the weather and its importance for the life of both humans and cattle, for example the impact of strong frost on the meadows and pastures, the beginning of goat pasture, the time of ascent of cattle to the alpine meadows and the begin of rye harvest (Zenhäuser 2008).

Christian Röthlisberger (born 1944) has a passion for observing the weather and plant development since his adolescence. During his activity as a general practitioner in the village of Grossaffoltern (Canton Bern) from 1977 to 2010 and since his subsequent retirement he carries out integrative meteorological measurements and weather observations in his region outside the official meteorological network as they are known in the historic past. In particular, he documents the development of a growing number of wild and cultivated plants including species missing in the official phenological network of MeteoSwiss. By doing so he establishes a phenological link between the present and the past which documents the Global Warming. Just two of his series are so far integrated in Euro-Climhist (module Switzerland).

The begin of (winter) rye harvest in the Swiss Mittelland 1454-1970
Prior to the early nineteenth century grain was reaped with sickles, subsequently scythes and finally harvest-binders were used. Under those conditions the beginning of harvest hinged on the stage of “yellow ripeness”, i.e. before the grain easily fell out of the ears. This stage mainly depends from temperatures between March and July (Wetter, Pfister 2011). The introduction of the combine harvester thresher (around 1970) radically changed grain harvesting, because a combine requires grain to be ripe seven to ten days before cutting.

Day-labourers engaged by the Basel hospital were paid at the end of every single working day according to the Book of Expenditures. This book was kept daily from 1454 to 1705 (with some gaps) and contains all relevant agricultural activities. For the period March to July temperatures may be assessed from this evidence.

Extract from the Book of Expenditures of the Basel Hospital on the year 1522: “Paid for harvesting work Friday after Margaret Day [28th July, 1522 according to the Gregorian calendar].” This date is ten days later than the long term average 1454 to 1970 which indicates low temperatures from March to July. This conclusion is supported with narrative data.

Between 1706 and the early nineteenth century the beginning of harvest is obtained from the date on which the tithe was auctioned. All peasants in a community had to begin the harvest the same day, amongst other things to prevent fraud in the delivery of the tenth sheaf in kind. Selling the collection of the grain tithe by auction to the highest bidder, usually to a member of the village elite, was a convenient solution. The successful bidder collected and threshed the tenth sheaf, to deliver the grain to the tithe barn. He could keep the remaining straw as a compensation for his work. Tithe protocols (so-called Zehntrödeln) from the late sixteenth century onwards contain the date of the auction and can, therefore, serve as a climate-historical source. In the early nineteenth century the tithe was abolished. Up to the mid-twentieth century the harvest date is known from records kept by farmers and weather diarists, afterwards from observations carried out within the phenological network of MeteoSwiss (series 15).

The ripening of grapes is closely related to temperatures from April to July. For the Swiss Mittelland those dates are preserved without gaps since 1501 (Wetter et al. 2013). Notes about the beginning of grape harvest and the so-called vineyard ban, a common practice since Roman times, are therefore valuable temperature proxies for the warm season. As soon as the grapes were ripe, the vineyards were banned, i.e. guarded day and night, to prevent clandestine harvesting at the expense of the owners and the church. This measure was established by the authorities of the community which were responsible for correct payment of dues. Lifting the grape harvest ban was a public act laid down in the municipal records, year for year, for centuries. In Burgundy, the oldest records go back to the thirteenth century. A long time series from 1444 to 2012 was published by Wetter and Pfister (2013) for Switzerland.

Lake Zurich froze over in early 1880 following two extremely cold months, the coldest ones since 1755. On 23th January, 1880 the ice was thick enough to carry people. A lake-freezing always gave young and old the opportunity to celebrate the event with sledge parties and skating exercises on the ice. Many Swiss lakes including Lake Constance, Lake Neuchâtel, most parts of Lake Lucerne and the southern end of Lake Geneva became ice-bound. After that of 1830, the winter 1880 is the coldest since 1755 (Pfister 1999: 103).

In severe winters the lakes in the Swiss Mittelland freeze according to their size, depth and individual particularities following a certain sequence: Shallower lakes like Lake Untersee, Lake Murten and Lake Biel will freeze earlier than deeper ones such as Lake Zug, Lake Zurich, Lake Constance (Upper Lake), Lake Neuchâtel and Lake Thun. A complete lake-freezing of Lake Lucerne, Lake Brienz, Lake Walensee and Lake Geneva is not documented for the time since 1501 (Pfister 1984). Smaller lakes also froze frequently in the warm twentieth century (Hendricks-Franssen, Scherrer 2008).