cc: Phil Jones , Thomas R Karl , Kevin Trenberth date: Tue, 24 Jun 2008 10:44:53 -0600 from: Aiguo Dai subject: Re: ET and PDSI to: trenbert@ucar.edu Kevin, Sorry to hear that. I tried to tone down the statements regarding the global implications of the results, as our CLM3-simulated soil moisture (forced by observed precip and temp, etc.) seems to support the conclusion based on our PDSI. The IPCC AR4 also shows (Fig. 10.12) that soil moisture will become drier at northern latitudes even though precip increases there. I think that the calculations of surface evaporation, runoff, soil moisture, and other land surface processes are much more sophisticated in current global climate models than in simple water balance models (like the Palmer model). Thus the climate model results avoid most of the issues dicussed by Hobbins et al. (e.g., related to ET calculation, effects of vegetation, snow cover, changes in humidity, radiation, and winds). Regards, Aiguo Aiguo Kevin Trenberth wrote: Aiguo I can't say that I like this paper at all. Kevin Hi, Phil, Our GRL paper finally has come out. Below is the ref. and a link. Best regards, Aiguo Hobbins, M. T., *A. Dai*, M. L. Roderick, and G. D. Farquhar, 2008: *Revisiting potential evapotranspiration parameterizations as drivers of long-term water balance trends. */Geophys. Res. Lett./, *35*, L12403, doi:10.1029/2008GL033840 (Paper) [1] Phil Jones wrote: Aiguo, Thanks. It wasn't me slowing the ms down! Another factor in addition to wind and radiation is vapour pressure. In case you've not seen the attached here it is. Vapour Pressue and q are going up as T goes up. RH stays much the same. We've submitted a longer paper on this dataset. It is rather short though - only going back to 1973. Cheers Phil At 16:49 14/02/2008, you wrote: Hi Phil, The manuscript is attached, which took a while to get through the review process, but look like it will be accepted after some revision. The main conclusion is that changes in wind speed and sfc radiation may be important in water balance calculation for wet regions. Because the PDSI model considers only T and P changes, its application over wet, energy-limited regions may be questionable. We still need to work out this on a global basis. On the other hand, the PDSI results from Dai et al. (2004) illustrate the potential drying from surface warming and precip changes alone, and this drying appears to have happened over many regions (e.g., most Africa, etc.). Aiguo Phil Jones wrote: Aiguo, I hear you're doing a paper with Hobbins, Roderick and Farquhar. Is it possible to send me a copy of this? Cheers Phil Prof. Phil Jones Climatic Research Unit Telephone +44 (0) 1603 592090 School of Environmental Sciences Fax +44 (0) 1603 507784 University of East Anglia Norwich Email [2]p.jones@uea.ac.uk [3] NR4 7TJ UK ---------------------------------------------------------------------------- -- Aiguo Dai, Scientist Email: [4]adai@ucar.edu [5] Climate & Global Dynamics Division Phone: 303-497-1357 National Center for Atmospheric Research Fax : 303-497-1333 P.O. Box 3000, Boulder, CO 80307, USA [6]www.cgd.ucar.edu/cas/adai/ [7] Street Address: 1850 Table Mesa Drive, Boulder, CO 80305, USA Prof. Phil Jones Climatic Research Unit Telephone +44 (0) 1603 592090 School of Environmental Sciences Fax +44 (0) 1603 507784 University of East Anglia Norwich Email [8]p.jones@uea.ac.uk NR4 7TJ UK ---------------------------------------------------------------------------- -- Aiguo Dai, Scientist Email: [9]adai@ucar.edu Climate & Global Dynamics Division Phone: 303-497-1357 National Center for Atmospheric Research Fax : 303-497-1333 P.O. Box 3000, Boulder, CO 80307, USA [10]www.cgd.ucar.edu/cas/adai/ Street Address: 1850 Table Mesa Drive, Boulder, CO 80305, USA ___________________ Kevin Trenberth Climate Analysis Section, NCAR PO Box 3000 Boulder CO 80307 ph 303 497 1318 [11]http://www.cgd.ucar.edu/cas/trenbert.html -- Aiguo Dai, Scientist Email: [12]adai@ucar.edu Climate & Global Dynamics Division Phone: 303-497-1357 National Center for Atmospheric Research Fax : 303-497-1333 P.O. Box 3000, Boulder, CO 80307, USA [13]www.cgd.ucar.edu/cas/adai/ Street Address: 1850 Table Mesa Drive, Boulder, CO 80305, USA