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Monday, October 13, 2008

Pablo Campra et al.: Surface temperature cooling trends and negative radiative forcing due to land use change toward greenhouse farming in SE Spain

Pablo Campra (Escuela Politécnica Superior, Universidad de Almeria, Almeria, Spain), Monica Garcia (Estación Experimental de Zonas Áridas (EEZA-CSIC), Almeria, Spain), Yolanda Canton (Departamento de Edafología y Química Agrícola, Universidad de Almeria, Almeria, Spain), and Alicia Palacios-Orueta (Escuela Técnica Superior de Ingenieros de Montes, Universidad Politecnica de Madrid, Madrid, Spain)

Received 4 February 2008; revised 15 May 2008; accepted 24 June 2008; published 23 September 2008.

Greenhouse horticulture has experienced in recent decades a dramatic spatial expansion in the semiarid province of Almeria, in southeastern (SE) Spain, reaching a continuous area of 26,000 ha in 2007, the widest greenhouse area in the world. A significant surface air temperature trend of –0.3 C/decade in this area during the period 1983–2006 is first time reported here. This local cooling trend shows no correlation with Spanish regional and global warming trends. Radiative forcing (RF) is widely used to assess and compare the climate change mechanisms. Surface shortwave RF (SWRF) caused through clearing of pasture land for greenhouse farming development in this area is estimated here. We present the first empirical evidences to support the working hypothesis of the development of a localized forcing created by surface albedo change to explain the differences in temperature trends among stations either inside or far from this agricultural land. SWRF was estimated from satellite-retrieved surface albedo data and calculated shortwave outgoing fluxes associated with either uses of land under typical incoming solar radiation. Outgoing fluxes were calculated from Moderate Resolution Imaging Spectroradiometer (MODIS) surface reflectance data. A difference in mean annual surface albedo of +0.09 was measured comparing greenhouses surface to a typical pasture land. Strong negative forcing associated with land use change was estimated all year round, ranging from –5.0 W/m to –34.8 W/m, with a mean annual value of –19.8 W/m. According to our data of SWRF and local temperatures trends, recent development of greenhouse horticulture in this area may have masked local warming signals associated to greenhouse gases increase.

Citation: Campra, P., M. Garcia, Y. Canton, and A. Palacios-Orueta (2008), Surface temperature cooling trends and negative radiative forcing due to land use change toward greenhouse farming in southeastern Spain, J. Geophys. Res., 113, D18109, doi:10.1029/2008JD009912.

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