Seite - 259 - in The Power of Urban Water - Studies in premodern urbanism

15 Human Impact onHydrology 259 But with regard to our topic of urban waters, the ecological consequences are far more important than the social ones.Prior to the introductionof regulatedcrop rotation, therewasa small landscapemosaicof enclosedplots cultivated individuallyby farmers. Settlements them- selves often shiftedover small distances, enablinganalternating landuse soas toprevent soil degradation.The introductionof theopen fieldsystemsawthe removalof fieldwallsandhedg- es,which in general hadbeennecessary because of the grazingduring fallowperiods. But the cooperation and coordination of crop rotation superseded the enclosure of every single field, becausewithin regulatedcrop rotation,herdsbelonging todifferent ownerswerekept together in the larger fieldblocks.This removalofhedgeschanged themicroclimateby increasingheath emission over large grain fields, by increased evaporation, and by increasing water run-off. Thus,a transformationof the rural landscape triggeredby thegrowthof townshadfar-reaching effects, amongotherson thehydrology.Geo-archaeological researchhasyieldedsomeevidence for increasedsoil erosion, resultingnotonly ingullying,butalso inchanges in thevalleys. The sedimentation of alluvial clay reduced streamvelocity, enlarged themeandering of creeks and rivers,andraised thegroundwater level in thevalleysand thedrier situationson thesurround- ing slopes. Increasing risksbyhydrological changes The highmedieval landscape changes, for which urbanisation was one factor among others, resulted in some risks for the local society.37 The increasing exposure of an open landscape with fewer hedges to soil erosion and the changingmicroclimatewere accompanied by some disturbances of the biotopes of small animals like rodents or birds. At the same time, yields of agrarian landmayhavedeclined, rather than increased, because the gainof landby the intro- ductionof theopen field systemmayhavebeenoffsetby the losses causedby themoreperma- nent cultivation of single land plots. We need to remember that the formation of the village marks the endof a shifting settlement system,whichmayhave contributed to sustainable soil management throughthealterationof landusebysettlementactivities,gardens,agrarian fields andsometimesmaybeevenwood-cutting.Within theopen field system,husbandrymeant that herds were held in common and therefore the risk of animal diseases becamemore serious. Looking at the 14th century, just a fewgenerations after these fundamental changeswithin the agrarian landscape, we can, in fact, see an increase in animal diseases, soil erosion and the subsequent abandonment ofmany rural settlements. This even raises the question ofwhether the outbreak of the Black Deathmay have had an anthropogenic component, as the extreme weatherof 1342 including the floodaroundStMaryMagdalene’sday in Julymayhavehadsome consequences for rodent populations, including the rats,whichwere an important reservoir of Yersinia pestis.38 New studies show that therewas a geneticmutation of this pathogen shortly before 1349 and that the introduction of Yersinia pestismay have been more complex than hitherto assumed.39 There isa lotofspeculation inthisscenariobynow,andweare far fromaconsistentpicture ofall the interconnectionsof the latemedieval crisis.Weneed toverifyor falsify thehypothesis of these long-term consequences of high medieval landscape changes by establishing more facts: 1) on the history of Yersinia pestis, because genetics indicate its presence in Europe al- ready in the 6th century. This raises the question if the 1347 outbreak spreading from the east interactedwithplaguegermspresent in central Europebefore 1347, 2) on the changesof biodi- versity and the living conditions of small animals, 3) on thephysical outline of fields and field 37 Schreg 2013a. 38 Schreg 2019. 39 Bos et al. 2011;Namouchi et al. 2018.