Historic maps as a data source for socio-hydrology: a case study of the Lake Balaton wetland system, Hungary

摘要

Socio-hydrology is the science of human influence on hydrology and theinfluence of the water cycle on human social systems. This newly emergingdiscipline inherently involves a historic perspective, often focusing ontimescales of several centuries. While data on human history is typicallyavailable for this time frame, gathering information on the hydrologicalsituation during such a period can prove difficult: measured hydrologicaldata for such long periods are rare, while models and secondary data setsfrom geomorphology, pedology or archaeology are typically not accurateenough over such a short time. In the first part of this study, the use ofhistoric maps in hydrology is reviewed. Major breakthroughs were theacceptance of historic map content as valid data, the use of preservedfeatures for investigating situations earlier than the map, and the onset ofdigital georeferencing and data integration. Historic maps can be primaryquantitative sources of hydro-geomorphological information, they can providea context for point-based measurements over larger areas, and they candeliver time series for a better understanding of change scenarios.In the second part, a case study is presented: water level fluctuations ofLake Balaton were reconstructed from maps, levelling logs and otherdocuments. An 18th century map system of the whole 5700 km2catchment was georeferenced, integrated with two 19th century mapsystems, and wetlands, forests and open water digitized. Changes in wetlandarea were compared with lake water level changes in a 220 yr time series.Historic maps show that the water level of the lake was closer topresent-day levels than expected, and that wetland loss pre-dates drainageof the lake.The present and future role of historic maps is discussed. Historichydrological data has to be treated with caution: while it is possible tolearn form the past, the assumption that future changes will be like pastchanges does not always hold. Nevertheless, old maps are relativelyaccessible data sets and the knowledge base for using them is rapidlygrowing, and it can be expected that long-term time series will beestablished by integrating georeferenced map systems over large areas.In the Appendix, a step-by-step guide to using historic maps in hydrology isgiven, starting from finding a map, through georeferencing and processingthe map to publication of the results.