1 A biophysical approach using water deficit factor for daily estimations of 2 evapotranspiration and CO2 uptake in Mediterranean environments 3 4 5 6 David Helman1,2,*, Itamar M Lensky1, Yagil Osem3, Shani Rohatyn4, Eyal Rotenberg4 and Dan 7 Yakir4 8 9 10 1 Department of Geography and Environment, Bar Ilan University, Ramat Gan 52900, Israel 11 2 Department of Geography, University of Cambridge, Cambridge, CB2 3EN, UK 12 3 Department of Natural Resources, Agricultural Research Organization, Volcani Center, Bet 13 Dagan 50250, Israel 14 4 Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot 76100, Israel 15 16 17 18 *Corresponding author: 19 David Helman (
[email protected] ;
[email protected]) 20 Department of Geography, Bar-Ilan University, Ramat Gan 52900 21 Israel. 22 Tel: +972 3 5318342 23 Fax: +972 3 5344430 1 24 Abstract 25 26 Estimations of ecosystem-level evapotranspiration (ET) and CO2 uptake in water-limited 27 environments are scarce and scaling up ground-level measurements is not straightforward. A 28 biophysical approach using remote sensing (RS) and meteorological data (RS-Met) is adjusted 29 to extreme high-energy water-limited Mediterranean ecosystems that suffer from continuous 30 stress conditions to provide daily estimations of ET and CO2-uptake (measured as gross 31 primary production – GPP) at a spatial resolution of 250-m. The RS-Met was adjusted using a 32 seasonal water deficit factor (fWD) based on daily rainfall, temperature and radiation data. We 33 validated our adjusted RS-Met with eddy-covariance flux measurements using a newly 34 developed mobile lab system and the single active Fluxnet station operating in this region 35 (Yatir pine forest station) in a total of seven forest and non-forest sites across a climatic transect 36 in Israel (280-770 mm y-1).