Water footprint and economic water productivity of sheep meat at farm scale in humid and semi-arid agro-ecological zones

Tunisia is prone to serious depletion of water resources that is threatening the sustainable agriculture development especially the livestock sector. The current study aimed to measure water footprint (WF) and economic water productivity (EWP) of sheep meat within twelve smallholder farms in two different agro-ecological zones in Tunisia; humid in northern and semi-arid in central Tunisia. A year-round monitoring of on-farm practices was performed using water meters and recording equipment's installed in key locations in the target sheep farms. The water source green (rainwater) and blue (from irrigation) corresponds to (i) water used for feed production, (ii) sheep watering, (iii) cleaning and servicing water, (v) water used for crop and pasture yield production, and (iv) economic and production performance. Results show that farms in semi-arid region have the highest WF averaging 9.07 ± 0.48 m3/ kg sheep body weight (BW) of which 8.58 ± 0.46 m3/kg BW was green water and 0.49 ± 0.05 m3/kg BW was blue water. The lowest WF values were recorded in farms in humid region averaging 6.98 ± 0.3 m3/kg BW out of 6.79 ± 0.27 m3/kg BW was green water. Around 17.3% of the total WF of sheep meat was attributed to virtual water from off-farm feed production in farms in humid region. However, in farms in the semi-arid region, the proportion of off-farm feed exceeds 65% and they are imported from international markets or produced in northern region. Most of the total volume of water (99%) refers to the WF of feed production. Drinking water, service and cleaning water account only for less than 1%. The assessment of the EWP revealed that farms had an average gross margin per m3 of water of 0.49 ± 0.1 US $ and US$ 0.29 ± 0.04 in humid and semi-arid regions, respectively. The current results confirm that producing sheep meat in humid region is 20% more efficient in term of water use and create 60% more gross margin return per m3 of water than in semi-arid region. In addition, semi-arid region is more prone to the impact of climate change that humid region. Moreover, rangeland degradation coupled with the high density of sheep flocks in the semi-arid region, mean that farms in the humid region would profit more from sheep rearing.