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Development and application of the Global Crop Water Model (GCWM)

The Global Crop Water Model (GCWM) has been developed to simulate crop water use in rainfed and irrigated agriculture. The model has a spatial resolution of 5 arc minutes by 5 arc minutes (about 9 x 9 km along the equator) and considers 26 distinct crop classes. Based on daily soil water balances crop water use is partitioned in evapotranspiration stemming from blue (irrigation) water or green (precipitation) water. Yield decrease in rainfed agriculture due to water scarcity is simulated based on the relationship between actual and potential crop evapotranspiration. Combined to statistical information on average crop yields per entity (country, federal state, province etc.) crop yields and crop water productivities in irrigated and rainfed agriculture are computed. The virtual water content of the crops will be linked to global trade information to simulate the related virtual water flows of blue and green water as induced by crop production.

The model was applied for the period 1998-2002. Input data, methodology and first results for irrigated agriculture are presented in Frankfurt Hydrology Paper 07. Results for rainfed crops, simulated crop yields in irrigated and rainfed agriculture, virtual water contents and the potential yield loss when not using irrigation are presented in another publication that is currently in press. The data will be made available on this web page soon.

Major sources of input data:

Cropping pattern, cropping seasons and average crop productivity:

MIRCA2000 data set developed by the own working group (University of Frankfurt)
cropland extent and harvested crop areas provided by the Global Land and Water Lab (McGill University Montreal) and SAGE (University of Wisconsin-Madison)
FAO Agro-MAPS database
FAOSTAT database

Climate:

Climate Research Unit (CRU) gridded data (University of East Anglia)

Soil:

ISRIC-WISE derived soil properties

Trade:

United Nations comtrade database

Results:

Consumption of blue and green water on cropland:

Total crop evapotranspiration was 6685 km³ yr^-1, of which blue water use was 1180 km³ yr^-1, green water use of irrigated crops was 919 km³ yr^-1 and green water use of rainfed crops was 4586 km³ yr^-1. Total crop water use was largest for rice (941km³ yr^-1), wheat (858 km³ yr^-1) and maize (722 km³ yr^-1). The largest amounts of blue water were used for rice (307 km³ yr^-1) and wheat (208 km³ yr^-1). Blue water use as percentage of total crop water use was highest for date palms (85%), cotton (39%), citrus fruits (33%), rice (33%) and sugar beets (32%), while for cassava, oil palm and cocoa, almost no blue water was used. Average crop yield of irrigated cereals was 442 Mg km^-2 while average yield of rainfed cereals was only 266 Mg km^-2. 43% of cereal production was on irrigated land, and without irrigation, cereal production on irrigated land would decrease by 47%, corresponding to a 20% loss of total cereal production. The largest cereal production losses would occur in Northern Africa(66%) and Southern Asia (45%) while losses would be very low for Northern Europe (0.001%) ==> see also our most recent publication in Journal of Hydrology.


total consumptive crop water use (mm/yr, averaged over total cell area) => download pdf [1.1 MB]	total consumptive water use of irrigated crops (mm/yr, averaged over total cell area) => download pdf [1.0 MB]

consumptive blue crop water use (mm/yr, averaged over total cell area) => download pdf [1.0 MB]	consumptive green crop water use (mm/yr, averaged over total cell area) => download pdf [1.1 MB]

consumptive green water use of irrigated crops (mm/yr, averaged over total cell area) => download pdf [1.0 MB]	consumptive water use of rainfed crops growing on areas equipped for irrigation (mm/yr, averaged over total cell area) => download pdf [0.9 MB]

consumptive blue water use of irrigated crops (mm/yr, averaged over irrigated cell area) => download pdf [1.0 MB]	consumptive blue water use of irrigated crops (% of total consumptive water use of irrigated crops) => download pdf [1.0 MB]

The results are described much more in detail in Frankfurt Hydrology Paper 07 and Siebert and Döll, in press (see the publications section below).

Publications:

Siebert, S. & Döll, P. (in press): Quantifying blue and green virtual water contents in global crop production as well as potential production losses without irrigation. Journal of Hydrology, DOI: 10.1016/j.jhydrol.2009.07.031.

Siebert, S. & Döll, P. (2008): The Global Crop Water Model (GCWM): Documentation and first results for irrigated crops. Frankfurt Hydrology Paper 07, Institute of Physical Geography, University of Frankfurt, Frankfurt am Main, Germany. [Download pdf, 11.4 MB]

Coming soon: