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  • Lobell, D.B., C. Bonfils, and J.M. Faures, 2007: The role of irrigation expansion in past and future temperature trends. Earth Interactions, in press. Submitted.

Expansion of irrigated land can cause local cooling of daytime temperatures by up to several degrees Celsius. Here we compare the expected cooling associated with rates of irrigation expansion in developing countries for historical (1961-2000) and future (2000-2030) periods with climate model predictions of temperature changes from other forcings, most notably increased atmospheric greenhouse gas levels, over the same periods. Indirect effects of irrigation on climate, via methane production in paddy rice systems, were not considered. In regions of rapid irrigation growth over the past 40 years, such as Northwest India and Northeast China, irrigation’s expected cooling effects have been similar in magnitude to climate model predictions of warming from greenhouse gases. A masking effect of irrigation can therefore explain the lack of significant increases in observed growing season maximum temperatures in these regions and the apparent discrepancy between observations and climate model simulations. Projections of irrigation for 2000-2030 indicate a slowing of expansion rates, and therefore cooling from irrigation expansion over this time period will very likely be smaller than in recent decades. At the same time, warming from greenhouse gases will likely accelerate, and irrigation will play a relatively smaller role in agricultural climate trends. In many irrigated regions, therefore, temperature projections from climate models, which generally ignore irrigation, may be more accurate in predicting future temperature trends than their performance in reproducing past observed trends would suggest.

Last Updated: 2008-02-06

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