Assessing the water challenge of a new green revolution in developing countries

TLDR

The study examines how meeting the 2015 UN Millennium Development Goal hunger target and feeding a growing population in 92 developing countries will affect water use, quantifying the roles of green (rain‑fed) and blue (irrigation) water and the potential for water‑productivity gains to ease freshwater pressure. Water requirements are expressed as vapor flows, with potential sources identified and impacts on agricultural land expansion and ecosystem trade‑offs analyzed, while the relative contributions of infiltrated rainwater and irrigation water to water productivity are quantified. Results show that halving hunger by 2015 and 2050 would require additional vapor flows of 2,200 km³ yr⁻¹ and 5,200 km³ yr⁻¹, respectively, that a nonlinear vapor‑flow–yield relationship in low‑yield savannas offers high water‑productivity potential, and that such gains could reduce extra water needs by 16 % in 2015 and 45 % by 2050, though most additional water would still come from rain‑fed production and cropland expansion of ~0.8 % yr⁻¹ would likely be unavoidable.

Abstract

This article analyzes the water implications in 92 developing countries of first attaining the 2015 hunger target of the United Nations Millennium Development Goals and then feeding a growing population on an acceptable standard diet. The water requirements in terms of vapor flows are quantified, potential water sources are identified, and impacts on agricultural land expansion and water tradeoffs with ecosystems are analyzed. This article quantifies the relative contribution from infiltrated rainwater/green water in rain-fed agriculture, and liquid water/blue water from irrigation, and how far water productivity (WP) gains can go in reducing the pressure on freshwater resources. Under current WP levels, another 2,200 km(3).yr(-1) of vapor flow is deemed necessary to halve hunger by 2015 and 5,200 km(3).yr(-1) in 2050 to alleviate hunger. A nonlinear relationship between vapor flow and yield growth, particularly in low-yielding savanna agro-ecosystems, indicates a high potential for WP increase. Such WP gains may reduce additional water needs in agriculture, with 16% in 2015 and 45% by 2050. Despite an optimistic outlook on irrigation development, most of the additional water will originate from rain-fed production. Yield growth, increasing consumptive use on existing rain-fed cropland, and fodder from grazing lands may reduce the additional rain-fed water use further by 43-47% until 2030. To meet remaining water needs, a cropland expansion of approximately 0.8% yr(-1), i.e., a similar rate as over the past 50 years (approximately 0.65% yr(-1)), seems unavoidable if food production is to occur in proximity to local markets.