Abstract
In this study we use long-term satellite, climate, and crop observations to document the spatial distribution of the recent stagnation in food grain production affecting the water-limited tropics (WLT), a region where 1.5 billion people live and depend on local agriculture that is constrained by chronic water shortages. Overall, our analysis shows that the recent stagnation in food production is corroborated by satellite data. The growth rate in annually integrated vegetation greenness, a measure of crop growth, has declined significantly (p < 0.10) in 23% of the WLT cropland area during the last decade, while statistically significant increases in the growth rates account for less than 2%. In most countries, the decade-long declines appear to be primarily due to unsustainable crop management practices rather than climate alone. One quarter of the statistically significant declines are observed in India, which with the world’s largest population of food-insecure people and largest WLT croplands, is a leading example of the observed declines. Here we show geographically matching patterns of enhanced crop production and irrigation expansion with groundwater that have leveled off in the past decade. We estimate that, in the absence of irrigation, the enhancement in dry-season food grain production in India, during 1982–2002, would have required an increase in annual rainfall of at least 30% over almost half of the cropland area. This suggests that the past expansion of use of irrigation has not been sustainable. We expect that improved surface and groundwater management practices will be required to reverse the recent food grain production declines.
Highlights
In the last 40 years, global crop production has more than doubled, supporting an increase in population of 3.2 billion people
The difference in trends of iNDVI for the two periods expressed in terms of percent change (Equation 2), shows that during 1996–2006 the growth rate of iNDVI declined by more than half over 58% of the water-limited tropics (WLT)
In this study we provided a satellite-based, independent assessment of the declines in growth rates of food grain production in the countries of the WLT reported by crop statistics
Summary
In the last 40 years, global crop production has more than doubled, supporting an increase in population of 3.2 billion people. This growth has been mainly possible through the innovations introduced by the Green Revolution, such as the use of high-yielding varieties of grain, massive increases in chemical fertilization (≈700%) [1], in irrigated area (100%) [2], and mechanization, and a modest (12%) increase in global cropland area. In spite of concerted international efforts to increase global food security [6], aggregated agricultural production statistics indicate that rates of food grain production have recently stalled or declined in several WLT countries [7,8], escalating concerns about matters of food security—the availability of food and access to it in a region where many people live in extreme poverty and depend on agrarian economies and local food production. We discuss the prospects for reversing these trends by examining the deceleration in food grain production in India, the country with the world’s largest population of food-insecure people and largest WLT croplands
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