Surface temperature cooling trends and negative radiative forcing due to land use change toward greenhouse farming in southeastern Spain
10 pages, 6 figures.-- Open Access full-text version available at the publisher's site. ; Index Terms: 1632 Global Change: Land cover change; 1631 Global Change: Land/atmosphere interactions; 0402 Biogeosciences: Agricultural systems; 1640 Global Change: Remote sensing; 3329 Atmospheric Processes: Mesoscale meteorology. ; 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−1 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−2 to −34.8 W m−2, with a mean annual value of −19.8 W m−2. 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. ; We thank the INM (Spanish National Institute of Meteorology), Cajamar Foundation, and IFAPA (JJAA) for providing climatic data. This work received financial support from several different research projects: PROBASE (CGL2006-11619/HID), funded by the Spanish Ministry of Education and Science; AQUASEM (P06-RNM-01732), funded by the Regional Government of Andalucia; DESIRE (Desertification, mitigation and remediation of land), funded by the European Commission. ; Peer reviewed