Geowissenschaften / Geographie
Fachbereich 11

While more and more information on the actual extent of irrigated agriculture has become available within the last decade and while the quality of the derived data products has been increasing significantly, information on the historical extent of irrigation is still very rare. Such information is required in particular for modelling slow changing systems like the global climate system, the global water cycle or decomposition processes in the soil. The models used here are often applied for periods lasting several decades or even centuries. A spatial data set showing the historical extent of irrigation is therefore requested to avoid simple ad-hoc assumptions for the historical irrigation extent.

The Hydrology group at the Institute of Physical Geography, University of Frankfurt, Germany, the Land and Water Lab at the Department of Geography, McGill University Montreal, Canada and the Bureau of  Economic Geology at the University of Texas at Austin, US cooperate therefore in the development of data layers indicating area equipped for irrigation back to year 1900. Data sets developed in the scope of this project as well as related documentation reports are made available for download on this web page.

Achievements

Irrigation statistics were collected and a data set of annual values of area equipped for irrigation for 236 countries in the world during the time period 1900 - 2003 was generated. The basis for this data product was information available through various online data bases and from other published materials. Six statistical methods (e.g. interpolation, extrapolation, scaling, estimate) were applied to fill data gaps or to harmonize inconsistent input data. It was found that the total area equipped for irrigation in the world in 1900 was about 53 million hectares, while it was about 286 million hectares in year 2003. Input data, methodology and results used in these estimates are described in detail in Frankfurt Hydrology Paper 08, that is available for download below. This document also contains a discussion of the expected uncertainty of the published estimates.

Coming soon

In the next step we will generate a data base of sub-national historical irrigation statistics. This data base can then be used to scale the areas in the Global Map of Irrigation Areas (reference period around year 2000) to obtain historical global irrigation maps. Additionally we will focus on the replacement of low confidence input data and estimates to reduce the overall uncertainty of the product. In a final step we also want to consider historical maps showing location and extent of irrigation areas in former times. This will allow to simulate changes of irrigation density inside the sub-national statistical units. We kindly ask all interested users of our products to help us by sending any comments, information and data that might contribute to this effort.