The papers that document the major role of landscape change on the climate continue to appear [h/t to Faisal Hossain!]. The latest important contribution is
Puma, M. J., and B. I. Cook (2010), Effects of irrigation on global climate during the 20th century, J. Geophys. Res., 115, D16120, doi:10.1029/2010JD014122.
The abstract reads
“Various studies have documented the effects of modern‐day irrigation on regional and global climate, but none, to date, have considered the time‐varying impact of steadily increasing irrigation rates on climate during the 20th century. We investigate the impacts of observed irrigation changes over this century with two ensemble simulations using an atmosphere general circulation model. Both ensembles are forced with transient climate forcings and observed sea surface temperatures from 1902 to 2000; one ensemble includes irrigation specified by a time‐varying data set of irrigation water withdrawals. Early in the century, irrigation is primarily localized over southern and eastern Asia, leading to significant cooling in boreal summer (June–August) over these regions. This cooling spreads and intensifies by century’s end, following the rapid expansion of irrigation over North America, Europe, and Asia. Irrigation also leads to boreal winter (December–February) warming over parts of North America and Asia in the latter part of the century, due to enhanced downward longwave fluxes from increased near‐surface humidity. Precipitation increases occur primarily downwind of the major irrigation areas, although precipitation in parts of India decreases due to a weaker summer monsoon. Irrigation begins to significantly reduce temperatures and temperature trends during boreal summer over the Northern Hemisphere midlatitudes and tropics beginning around 1950; significant increases in precipitation occur in these same latitude bands. These trends reveal the varying importance of irrigation‐climate interactions and suggest that future climate studies should account for irrigation, especially in regions with unsustainable irrigation resources.”
The paper concludes with the text
“Future efforts to understand irrigation in a climate model setting should not only carefully document the amount of irrigation water applied to the land, but also keep track of the relative amounts of surface water and groundwater used for irrigation. This irrigation water accounting will promote improved regional predictions of climate for future climate scenarios, especially if widespread depletion of groundwater occurs in the future. Ultimately, other human modifications to the hydrological cycle (e.g., reservoirs) should be incorporated into the next generation of climate models to identify areas that will be subjected to future water availability stress and elucidate the feedbacks between human water use and climate.”
This paper further documents the role of human land management as a first order climate forcing as discussed, for example, in
Pielke Sr., R.A., 2005: Land use and climate change. Science, 310, 1625-1626.