| dc.description.abstract | Fresh water consumption increases with a growing world population and a switch to more water resource demanding diets. Agriculture accounts for 92% of humanity’s water footprint (WF) (Hoekstra & Mekonnen, 2012). Therefore,a high potential in increasing water availability lies in decreasing the consumptive WF of crop production. The reference level to which the WF can be brought back is the water footprint benchmark (WFB). The WFB is the WF in m3/ ton of yield that is grown under non-stressed conditions using the most water conserving cultivation practices. The development of WFBs has only started in 2013 and is therefore in an early stage. The objective of this research is to investigate if climate, soil or type of hydrological year give rise to the need to distinguish WFBs and how this is related to the physical environment and its interaction with the crop. To explore the differences in WFB caused by these environmental factors, WFBs were defined by performing a modeling study in AquaCrop, a crop growth model based on the water balance, developed by the FAO. A 30-year time series (1960-1990) of WFs were simulated for four crops (maize, wheat, potato and cotton) under“best practice”, i.e.optimal growth conditions and most water efficient irrigation method in terms of resulting water productivity of the crop combined with organic mulching. Per crop, 16 scenarios with different climate-soil combinations were formulated (combining four climates from the Köppen-Geiger classification,Cfb, Af, Aw, Bsh, and four different soils, from low to high saturated hydraulic conductivity, namely clay, clay loam, silt, sand).The results suggest that it is relevant to distinguish WFBs based on climate, but not on soil type. No ground to distinguish WFBs for type of hydrological year was found as no strong relationship was observed between the WF and total precipitation over the growing season. WFBs need to be specified per type of climate because the weather pattern and total evaporative demand of the atmosphere over the growing season significantly affect both ET and Y and thus WFB. As no specific correlation between WF and hydrological year could be recognized, it is suggested to set the WFB at the highest best-practice WF that was found over of the 30-year study period. These WFBs are all lower than global WFBs resulting from a previous study. Therefore, this study suggests that if a crop is cultivated under best practice,it is reasonable to set WFBs lower than as yet established. Generally, a higher total atmospheric demand for water vapor over the growing season requires higher WFBs. Temperature seasonality can decrease the WFB and low temperatures can lead to cold stress and a higher WFB. The current research has focused on full irrigation.Under rain-fed conditions or supplemental or deficit irrigation, water stress could become important and the type of soil and hydrological year more relevant when specifying WFBs. | |
