Articles | Volume 7, issue 4
Earth Syst. Dynam., 7, 863–876, 2016
Earth Syst. Dynam., 7, 863–876, 2016

Research article 10 Nov 2016

Research article | 10 Nov 2016

Ocean–atmosphere interactions modulate irrigation's climate impacts

Nir Y. Krakauer1, Michael J. Puma2,3,4, Benjamin I. Cook3, Pierre Gentine5, and Larissa Nazarenko2,3 Nir Y. Krakauer et al.
  • 1Department of Civil Engineering and NOAA-CREST, The City College of New York, New York, NY 10031, USA
  • 2Center for Climate Systems Research, Columbia University, New York, NY 10025, USA
  • 3NASA Goddard Institute for Space Studies, New York, NY 10025, USA
  • 4Center for Climate and Life, Columbia University, Palisades, NY 10964, USA
  • 5Earth and Environmental Engineering, School of Engineering and Applied Science, Columbia University, New York, New York, USA

Abstract. Numerous studies have focused on the local and regional climate effects of irrigated agriculture and other land cover and land use change (LCLUC) phenomena, but there are few studies on the role of ocean–atmosphere interaction in modulating irrigation climate impacts. Here, we compare simulations with and without interactive sea surface temperatures of the equilibrium effect on climate of contemporary (year 2000) irrigation geographic extent and intensity. We find that ocean–atmosphere interaction does impact the magnitude of global-mean and spatially varying climate impacts, greatly increasing their global reach. Local climate effects in the irrigated regions remain broadly similar, while non-local effects, particularly over the oceans, tend to be larger. The interaction amplifies irrigation-driven standing wave patterns in the tropics and midlatitudes in our simulations, approximately doubling the global-mean amplitude of surface temperature changes due to irrigation. The fractions of global area experiencing significant annual-mean surface air temperature and precipitation change also approximately double with ocean–atmosphere interaction. Subject to confirmation with other models, these findings imply that LCLUC is an important contributor to climate change even in remote areas such as the Southern Ocean, and that attribution studies should include interactive oceans and need to consider LCLUC, including irrigation, as a truly global forcing that affects climate and the water cycle over ocean as well as land areas.

Short summary
We simulated effects of irrigation on climate with the NASA GISS global climate model. Present-day irrigation levels affected air pressures and temperatures even in non-irrigated land and ocean areas. The simulated effect was bigger and more widespread when ocean temperatures in the climate model could change, rather than being fixed. We suggest that expanding irrigation may affect global climate more than previously believed.
Final-revised paper