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Hydrological and Agricultural Responses of China's Loess Plateau to Predicted Climate Change
Volume 9, Number 15: 12 April 2006

Comprising some 380,000 square kilometers of semiarid to sub-humid land in the middle reaches of the Yellow River, China's Loess Plateau "is one of the most eroded regions in the world because of highly erodible soils, steep slopes, heavy storms, and low vegetation cover," according to Zhang and Liu (2005). In fact, every year an average of 1.5 billion tons of eroded sediments are carried downstream; and the two scientists say that "the prominent problems of flood control in the lower reaches of the Yellow River and soil deterioration resulting from soil erosion in the middle reaches are of great concern to the Chinese government." What is more, they state that "the potential impacts of climate change on the fragile and vulnerable ecosystems on the Loess Plateau may further complicate and exacerbate the existing problems."

This introduction to Zhang and Liu's new study follows a format that is often employed by climate alarmists. It identifies a "fragile and vulnerable" situation and suggests it will be made even worse - exacerbated, in the parlance of Zhang and Liu - by changes in climate predicted to result from continued anthropogenic CO2 emissions, whereupon an analysis follows that seems to support that contention. Hence, we expected to find much the same thing as we continued reading the new report; but we were pleasantly surprised to find that the researchers were unafraid to break free of the climate-alarmist mindset when their work suggested a significantly different outcome.

So what did Zhang and Liu do? ... and what did they find?

With respect to the first question, they used the general circulation model of the UK Meteorological Office's Hadley Centre to calculate expected changes in temperature and precipitation for the Chinese Loess Plateau over the next century, which exercise yielded 2.3-4.3C increases in maximum daily temperature, 3.6-5.3C increases in minimum daily temperature, and 23-37% increases in annual precipitation. They then used a stochastic weather generator to downscale these monthly projections to daily values, after which the Water Erosion Prediction Project model of Flanagan and Nearing (1995), as modified to account for CO2 effects on evapotranspiration and biomass production by Favis-Mortlock and Savabi (1996), was finally run for a wheat-wheat-corn rotation utilizing either conventional or conservation tillage.

With respect to the second question, Zhang and Liu determined that the climate-change scenarios they investigated led to 29-79% more water runoff and 2-81% greater soil loss under conventional tillage practices, but that "adoption of the conservation tillage could reduce runoff by 18-38% and decrease soil loss by 56-68% as compared to the conventional tillage under the present climate." Consequently, they concluded that "the use of the conservation tillage would be sufficient to maintain low runoff and erosion levels and thus protect agro-ecosystems under projected climate changes." As for all-important crop production, they determined that the warmer, wetter and CO2-enriched environment projected to prevail on the Chinese Loess Plateau a hundred years from now would actually boost yields, and by rather significant amounts: 15-44% for wheat and 40-58% for corn.

At the end of the day, therefore, Zhang and Liu were very upbeat about the future, noting that "the significant increases in predicted wheat and maize yields [which] were results of increased precipitation and CO2 concentration ... outweighed the negative effect of temperature rise on crop growth." And, we might add, they did it in spectacular fashion.

Sherwood, Keith and Craig Idso

References
Favis-Mortlock, D.T. and Savabi, M.R. 1996. Shifts in rates and spatial distribution of soil erosion and deposition under climate change. In: Anderson, M.G. and Brooks, S.M. (Eds.). Advances in Hillslope Processes. John Wiley, New York, New York, USA, pp. 529-560.

Flanagan, D.C. and Nearing, M.A. (Eds.). 1995. USDA-Water Erosion Prediction Project: Hillslope Profile and Watershed Model Documentation. National Soil Erosion Research Laboratory Report No. 10. NSERL, West Lafayette, Indiana, USA.

Zhang, X.-C. and Liu, W.-Z. 2005. Simulating potential response of hydrology, soil erosion, and crop productivity to climate change in Changwu tableland region on the Loess Plateau of China. Agricultural and Forest Meteorology 131: 127-142.