LETTER Hydrology, forests and precipitation recycling: a reply to van der Ent et al. DAVID ELLISON* † , MARTYN N. FUTTER ‡ andKEVIN BISHOP ‡ § *Institute for World Economics, Research Centre for Economic and Regional Studies, Hungarian Academy of Sciences, Budapest, Hungary, †Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umea ˚, Sweden, ‡Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden, §Department of Earth Sciences, Uppsala University, Uppsala, Sweden Keywords: climate change adaptation, ecosystem services, forests, precipitation recycling, water yield Received 1 June 2012 and accepted 13 June 2012 We warmly welcome the debate our article on the relationship between forest cover and water yield has inspired. Our principal goal was to illustrate how the local scale focus on demand by trees has overshadowed the larger scale role of forest cover in supplying the atmosphere with moisture, so as to address and hope- fully resolve the persistent and broad contradictions found in this literature. Furthermore, we thank the commentary authors for their strong support of the overall goal of our work. We read with general satisfac- tion their view that: ‘Ellison et al. (2012a) [have] initi- ated an important shift in thinking of forests as water suppliers, instead of mere water users’. On the other hand, we regret that we are required to point out and correct a number of misplaced criticisms and misrepresentations of our work. To say, for exam- ple, that we assume that evapotranspiration is ‘equal to green water transpired by plants and trees’ or that all of the water transpired by trees ‘returns to the conti- nents and none of it is transported back to the ocean’ is simply untrue. Moreover, our interest in illustrating and defending general principles has kept us from going into some of the details raised by the commen- tary authors (e.g. geographic variation in the thermal envelope), details we otherwise welcome and hope to see more of in future debates. To avoid the risk of misrepresenting the commentary authors, we include direct quotes in what follows where appropriate: The commentary authors repeatedly suggest our, ‘general reasoning is that total continental evapo- ration E [ET in (our) paper] can be assumed to be equal to green water transpired by plants and trees and thus (that we) neglect all-important nonpro- ductive evaporation fluxes’. We have nowhere made this assumption and are troubled by this erroneous critique of our work. We have consciously, consistently and carefully chosen the term ‘evapotranspiration’ or ET. In doing so, we explic- itly recognize both productive transpiration and non- productive evaporation fluxes by insisting on the term ‘ET’ (as opposed to either ‘E’, or transpiration) through- out our text. We note explicitly at the outset of our article that ET is composed of two specific elements (transpiration and evaporation). Moreover, we clearly indicate that trees and forests have considerable potential for increasing ET compared with other forms of productive and nonproductive evaporative flows. Table 1 (a, b) (Ellison et al., 2012a: 810), explicitly distinguishes different ET flux compo- nents and estimates their evaporative efficiency. As this table clearly demonstrates, our article recognizes that there are other potential sources of terrestrial E and/or ET (productive and nonproductive) besides that gener- ated by trees and compares them to each other in terms of their potential impact on the ET regime. Although the data we cite in Table 1a may not explic- itly distinguish between the transpiration and evapora- tion components of ET, our sources explicitly refer to ‘ET’. We fully agree with the commentary authors that interception from trees is important. And we have con- sistently considered interception as a component of ET. Discussing this distinction in greater detail, however, would have required significantly more space than per- mitted. We had to draw a line somewhere at the degree of detail in the article. As van der Ent et al., 2010 them- selves note, ‘it would be interesting to compute the dif- ferent contributions to moisture recycling… from interception, soil evaporation…’, (2010: 11). We assume the commentary authors agree it is difficult to do this in Correspondence: David Ellison, Institute for World Economics, Budao ¨ rsi u ´ t 45, 1112 Budapest, Hungary, tel. +36 1 309 2643, fax +36 1 309 2624, e-mail: ellisondl@gmail.com 3272 © 2012 Blackwell Publishing Ltd Global Change Biology (2012) 18, 3272–3274, doi: 10.1111/gcb.12000