cc: Keith Briffa date: Fri, 20 May 2005 05:36:23 -0400 (EDT) from: Alan Robock subject: Re: your presentation at EGU to: Gerard van der Schrier Content-Type: TEXT/PLAIN; CHARSET=iso-8859-1; FORMAT=flowed Content-ID: X-MIME-Autoconverted: from 8bit to quoted-printable by envsci.rutgers.edu id j4K9aSOI013920 Dear Gerard, Thanks for your interesting results. I guess I would conclude that you have discovered limitations to the PDSI model that raise questions as to how well it simulates long-term trends. It means, I think, that more information than temperature and precipitation are needed for such calculations. It makes me wonder how good tree-ring reconstructions of drought are that are based only on PDSI. Alan ------------------------------------------------------------------------ (remove 0 when calling from On sabbatical, Jan. 20 - June 30, 2005, at outside France) Cell: +33-(0)6-7229-8903 Laboratoire de Météorologie Dynamique Phone: +33-(0)1-4427-4763 Université Pierre et Marie Curie, Case Courrier 99 Fax: (0)1-4427-6272 Couloir 45-55, 3eme étage, E-mail: robock@envsci.rutgers.edu 75252 Paris Cedex 05, FRANCE http://envsci.rutgers.edu/~robock ------------------------------------------------------------------------ Alan Robock, Professor II Department of Environmental Sciences Phone: +1-732-932-9478 Rutgers University Fax: +1-732-932-8644 14 College Farm Road E-mail: robock@envsci.rutgers.edu New Brunswick, NJ 08901-8551 USA http://envsci.rutgers.edu/~robock On Fri, 20 May 2005, Gerard van der Schrier wrote: > Dear Alan, > > Thanks very much for the suggestions to improve the presentation. I agree > that the quality of the slides were horrible. It all seemed o.k. when I > produced them at the office though. > > Unfortunately, I've missed the opportunity to shake hands during the coffee > break. What I would have liked to say is that I really liked your recent GRL > article and the presentation at the EGU meeting. The absence of a trend > toward increased summer drought we observe in our PDSI records, was nice to > see confirmed in your soil moisture records form the Ukraine. > > Following a suggestion made by somebody in the audience, I computed the > self-calibrating PDSI for the area in the Ukraine from which you have the > records of soil moisture data. (June-July-August, averaged over 22-40E, > 46-52N) The figure is attached to this mail, and it shows a clear trend from > the mid-1940s to the early 1980s toward increased availability of soil > moisture. This is similar to your fig. 2a. However, instead of remaining > more-or-less constant from the mid 1980s onwards, the PDSI shows a rather > abrupt transition to slightly dry conditions and remains more-or-less > constant until 2002 (perhaps with a slight trend towards wetter conditions). > (alanrobock.eps) > > When averaging the CRU temperature and precipitation datasets over the same > area (for the preceeding JFMAMJJA months), a similar trend toward wetter > conditions in precipitation is found as in your figure 2b. From the early > 1980s, there is a steep trend toward less precipitation, coupled to > persistent and very high temperatures, which explains the change in the > scPDSI curve. (alanrobock2.eps) > > Best Regards, > Gerard > --------------------------------------- > Dr. G. van der Schrier > Climatic Research Unit > University of East Anglia > Norwich NR4 7TJ > UK > g.schrier@uea.ac.uk > www.uea.ac.uk/~f029 > --------------------------------------- > > > > > >