by Melanchthon
Tue Feb 14th, 2012 at 05:39:10 AM EST
Irrigated Agriculture: What countries are in danger?
Hat tip: Agriculture irriguée : quels pays sont en danger ? Libération {sciences²}
Agriculture requires water, and irrigation is growing. But where is this technique unsustainable because it uses non-renewable [water] stocks? This is the question answered by a long article published in the journal Water Resources Research . A disturbing answer, because it shows that regions - even entire countries - important in terms of agricultural production have increasingly recourse to unsustainable irrigation. The impact of an agricultural water crisis due to the unsustainable use could extend beyond these regions and could have effects at global level, say the authors of this study.
front-paged by afew
Much of water used for irrigation comes from nonsustainable sources
Some of the water used for irrigation comes from renewable sources such as local precipitation, rivers, lakes, and renewable groundwater. But some comes from nonrenewable groundwater sources. Because water supply for irrigation is so essential to the world's food supply, it is important to quantify how much water comes from sustainable sources. Wada et al. (2012) conducted a global assessment of how much water used for irrigation comes from nonsustainable groundwater sources. They used a global hydrological model to simulate the amount of water needed for optimal crop growth and the amount available from renewable sources. They combined this information with country-level data on groundwater use to estimate the amount of groundwater used for irrigation that comes from nonrenewable sources. Their results show that about 20%, or 234 km3 yr-1, of the water used for irrigation worldwide in 2000 came from nonrenewable sources. The countries with the highest levels of nonrenewable groundwater use are India, Pakistan, the United States, Iran, China, Mexico, and Saudi Arabia. Furthermore, worldwide, the use of groundwater from nonrenewable sources more than tripled from 1960 to 2000.
Abstract: Nonsustainable groundwater sustaining irrigation: A global assessment
Key Points- Global assessment of non-sustainable groundwater abstraction for irrigation
- Non-sustainable groundwater globally contributes 20% to irrigation
- Increasing dependency on non-sustainable groundwater in recent years
Water used by irrigated crops is obtained from three sources: local precipitation contributing to soil moisture available for root water uptake (i.e., green water), irrigation water taken from rivers, lakes, reservoirs, wetlands, and renewable groundwater (i.e., blue water), and irrigation water abstracted from nonrenewable groundwater and nonlocal water resources. Here we quantify globally the amount of nonrenewable or nonsustainable groundwater abstraction to sustain current irrigation practice. We use the global hydrological model PCR-GLOBWB to simulate gross crop water demand for irrigated crops and available blue and green water to meet this demand. We downscale country statistics of groundwater abstraction by considering the part of net total water demand that cannot be met by surface freshwater. We subsequently confront these with simulated groundwater recharge, including return flow from irrigation to estimate nonrenewable groundwater abstraction. Results show that nonrenewable groundwater abstraction contributes approximately 20% to the global gross irrigation water demand for the year 2000. The contribution of nonrenewable groundwater abstraction to irrigation is largest in India (68 km3 yr−1) followed by Pakistan (35 km3 yr−1), the United States (30 km3 yr−1), Iran (20 km3 yr−1), China (20 km3 yr−1), Mexico (10 km3 yr−1), and Saudi Arabia (10 km3 yr−1). Results also show that globally, this contribution more than tripled from 75 to 234 km3 yr−1 over the period 1960-2000.
Click on picture to enlarge
The authors' conclusion:
We argue that the unsustainability of groundwater use for irrigation is an important issue not only for the countries with intensive groundwater use, but also for the world at large since international trade directly links food production in one country to consumption in another. Rising population and their food demands are likely to increase the amount of nonrenewable groundwater abstraction for irrigation, particularly in emerging countries such as India, Pakistan, China, Iran and Mexico. This will result in falling groundwater levels which may eventually become unreachable for local farmers with limited technology.
Full article with maps and graphs (pdf)
Another article from the same authors:
Global depression of groundwater resources (pdf)
