Abstract
Water vapor radiative effects (WVRE) at surface in the long-wave (LW) and short-wave (SW) spectral ranges under cloud and aerosol free conditions are analyzed for seven stations in Spain over the 2007–2015 period. WVRE is calculated as the difference between the net flux obtained by two radiative transfer simulations; one with water vapor from Global Positioning System (GPS) measurements and the other one without any water vapor (dry atmosphere). The WVRE in the LW ranges from 107.9 Wm 2 to 296.7 Wm − 2 , while in the SW it goes from − 64.9 Wm − 2 to − 6.0 Wm − 2 . The results show a clear seasonal cycle, which allows the classification of stations in three sub-regions. In general, for total (SW + LW) and LW WVRE, winter (DJF) and spring (MAM) values are lower than summer (JJA) and autumn (SON). However, in the case of SW WVRE, the weaker values are in winter and autumn, and the stronger ones in summer and spring. Positive trends for LW (and total) WVRE may partially explain the well-known increase of surface air temperatures in the study region. Additionally, negative trends for SW WVRE are especially remarkable, since they represent about a quarter of the contribution of aerosols to the strong brightening effect (increase of the SW radiation flux at surface associated with a reduction of the cloud cover and aerosol load) observed since the 2000s in the Iberian Peninsula, but with opposite sign, so it is suggested that water vapor could be partially masking the full magnitude of this brightening.
Highlights
Water vapor is acknowledged as a crucial element in the climate system
In order to study the spatial variability of the Water vapor radiative effects (WVRE), the sites have been divided into three groups: North Atlantic (NA), Mediterranean Sea (MS) and Interior (I)
These groups have a geographical meaning (NA are stations close to the North Atlantic Sea, in Nothern Spain; I stations are in the interior of Iberia, and MS stations are close to the Mediterranean Sea in the East and South of Iberia)
Summary
Water vapor is acknowledged as a crucial element in the climate system. Its latent heat has an important role in energy transport and it is obviously a fundamental part of the hydrological cycle [1]. The infrared absorption of water vapor involves a positive feedback [2,3]. If the atmosphere’s temperature rises, the air can hold more water vapor from evaporation, since the saturation vapor pressure increases as temperature rises. This further increases the temperature of the climate system because of water vapor heating. The anthropogenic emissions of water vapor have no significant effect on the global climate, except those in the stratosphere, where due to the conditions of stability, pressure and temperature, water vapor emissions manage to stay in the long term, and can be considered a forcing [4,5,6,7]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
