Climate change signals in the historical water footprint of wheat production in Zimbabwe.

Climate change has been posited as the biggest threat to crop productivity in agro-systems, yet its impact on the water footprints of crop production for many regions remains uncertain. This study sought to determine evidence of historical climate change (1980-2010) and its resultant impact on the blue water footprint of winter wheat production in Zimbabwe. The analysis involved assessing the impact of climate change on wheat yield and crop water requirements, the key factors determining the blue water footprint. The CROPWAT model and the global water footprint assessment (WFA) standard were used to calculate the blue water footprint. Multiple linear regression was used to correlate climate variables to wheat yield, crop water requirements and the blue water footprint. Results show a significant (p < 0.05) warming of temperatures in the country's main wheat growing areas. Crop water requirements for winter wheat decreased by 4.88%, due to positive and negative trends in humidity and wind speed respectively. Between 1980 and 2000 the coupled effects of solar radiation at anthesis and maximum temperatures in July, August and September reduced wheat yields by 6.65%. The cumulative effects of climate change on crop water requirements and wheat yields increased the blue water footprint by 4%. The results of the study suggest that climate change and agricultural management factors might be equally responsible for the increase in the blue water footprint.