Water Footprint Assessment is a quickly growing field of research, but as yet little attention has been paid to the uncertainties involved. This study investigates the sensitivity of water footprint estimates to changes in important input variables and quantifies the size of uncertainty in water footprint estimates. The study focuses on the green and blue water footprint of producing maize, soybean, rice and wheat in the Yellow River Basin in the period
 1996-2005. A grid-based daily water balance model at a 5 by 5 arc minute resolution was applied to compute green and blue water footprints of the four crops in the Yellow River Basin in the period considered. The sensitivity and uncertainty analysis focused on the effects on water footprint estimates at basin level (in m3/ton) from four key input variables: precipitation (PR), reference evapotranspiration (ET0), crop coefficient (Kc) and crop calendar. The one-at-a-time method was carried out to analyse the sensitivity of the water footprint of crops to changes in the input variables. Uncertainties in crop water footprint estimates were quantified through Monte Carlo simulations.
 The results show that the water footprint of crops is most sensitive to ET0 and Kc, followed by crop calendar and PR. Blue water footprints were more sensitive to input variability than green water footprints. The smaller the annual blue water footprint, the higher its sensitivity to changes in PR, ET0 and Kc. The uncertainties in the total water footprint of a crop due to combined uncertainties in climatic inputs (PR and ET0) were about ± 20% (at 95% confidence interval). The effect of uncertainties in ET0 was dominant compared to that of precipitation. The uncertainties in the total water footprint of a crop as a result of combined key input uncertainties were on average ± 26% (at 95% confidence level). The sensitivities and uncertainties differ across crop types, with highest sensitivities and uncertainties for soybean.

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Sensitivity and uncertainty in crop water footprint accounting: a case study for the Yellow River Basin

Natural and anthropogenic influences on the recent droughts in Yellow River Basin, China.

The projected growth in global food demand until mid-century will challenge our ability to continue recent increases in crop yield and will have a significant impact on natural resources. The water and land requirements of current agriculture are significantly less than global reserves but local shortages are common and have serious impacts on food security. Recent increases in global trade have mitigated some of the effects of spatial and temporal variability. However, trade has a limited impact on low-income populations who remain dependent on subsistence agriculture and local resources. Potential adverse environmental impacts of increased agricultural production include unsustainable depletion of water and soil resources, major changes in the global nitrogen and phosphorous cycles, human health problems related to excessive nutrient and pesticide use, and loss of habitats that contribute to agricultural productivity. Some typical case studies from China illustrate the connections between the need for increased food production and environmental stress. Sustainable options for decreasing food demand and for increasing production include reduction of food losses on both the producer and consumer ends, elimination of unsustainable practices such as prolonged groundwater overdraft, closing of yield gaps with controlled expansions of fertilizer application, increases in crop yield and pest resistance through advances in biotechnology, and moderate expansion of rain fed and irrigated cropland. Calculations based on reasonable assumptions suggest that such measures could meet the food needs of an increasing global population while protecting the environment.

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1002/2015WR017053

Food security and sustainable resource management

Water scarcity in the Yellow River Basin under future climate change and human activities.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2017WR022090

Reservoir Operations to Mitigate Drought Effects With a Hedging Policy Triggered by the Drought Prevention Limiting Water Level

The Yellow River basin is a key food production centre of global importance facing rapidly growing water scarcity. Water availability for agriculture in the basin is threatened by rapid growth in the demand for industrial and urban water, the need to flush sediment from the river's lower reaches, environmental demands and growing water pollution. Climate change is already evident in the basin with long-term declines in river runoff, higher temperatures, and increasing frequency and intensity of drought. The Chinese government has exhausted most options for improving water supply. The challenge will be to switch to improved water demand management, which is hampered by existing governance structures, and lack of integrated agriculture and water resource policies.

Gu Xiaowei

Papers

Yellow River basin: living with scarcity.