From	Mike Hulme	Date	Sat, 8 May 2004 07:59:14 +0100
To	Aiguo Dai
CC	jprospero@rsmas.miami.edu, Mike Hulme, Phil Jones, plamb@ou.edu, Kevin Trenberth
Subject	denial or delusion? ... Aiguo's response
Dear Aiguo, You've done a great job in putting this together so quickly and clearly. I have a couple of additional comments to make on it, but can't do so until Tuesday. You (we?) might also like to think of the reply being multi-authored, including Phil, Pete, Kevin, Joe and myself. I must say that when I first read this paper a couple of weeks ago I wrote it off as so bad (so, so bad) that it didn't even deserve a response. To pretend that the Sahel drought didn't happen (i.e., a pure artifact of wrongful use of rainfall data) is the most astounding assertion, almost on a par with holocaust denial. Try putting that proposition to the millions of inhabitants of the Sahel in the 1970s, 1980s and 1990s, many of whom died as a direct consequence and whose livelihoods were devastated. Adrian Chappell may never have visited the region, but I know Clive Agnew has (many times) - and he should know better. I did my PhD research in the region in the early 1980s and I know exactly what the rainfall conditions were like and how much oridinary people suffered as a consequence. My PhD was on rainfall variability and local water supplies in Sudan and I visited and talked to many villagers in the region. Anyway, Phil first suggested that a corrective reply was needed and I can see the value of doing so, especially with IPCC AR4 approaching. It just seems to me such a shame that such poor science is being done by some people - in this case I don't think there is a deeper motive on the part of Chappell and Agnew than pure delusion and incompetence - and, worse, that a journal like IJC will publish it. Thanks again for your efforts, Mike >===== Original Message From Aiguo Dai ===== >Dear All, > >Soon after I sent out my last email, I quickly realized that there is >another fundamental error in their rainfall model eq.(1): the regional >station numbers na and nb should be replaced with regional areas. This >can be seen clearly in the following example: suppose region a has only >one station whose long-term mean rainfall happens to be the same as >region a's mean, and region b has 100 stations. Then their model would >give the completely wrong estimate of rainfall for region (a+b), while >the area-weighted version would still work. This is an obvious error, but >it apparently could be easily overlooked. Their model seems to be >originated from their incorrect perception that regional rainfall has >been traditionally derived using the simple arithmetic mean of all station >data. After reading the leader author's response to Joe's comments, I >could not believe that they still think previous analyses are simpler than >theirs! > >I also forgot to point out in my earlier draft the fact that even if their >modelled time series were a reasonable proxy of Sahel rainfall, their >results would still have had little implications to previous analyses of >Sahel rainfall. This is because their analysis maximized the effects of >changing station networks by the design of their model and by choosing >the boundary of the two sub-Sahel region at 6deg.W, whereas in most previous >analyses these effects were minimized by area-weighted averaging (Jones and >Hulme, 1996). > >Sorry for the overlook of these issues in my earlier email. > >Regards, > >--Aiguo Dai > > > > > >> Dear All, >> >> I was asked by Kevin to work out a rebuttal to Chappell and Agnew >> (2004). After reading >> it a couple of times, I found the main reason why they came to their >> results: they devised a >> Sahel rainfall model (eq. 1) with a necessary condition that the >> constants a and b >> represent the mean rainfall for the west and east part of the Sahel. >> However, later in their >> paper, they estimated a and b by a non-linear least-squares fitting to >> observed rainfall >> data, and their a (=973mm) and b (=142mm) are nowhere near the actural >> mean rainfall >> for these sub-Sahel regions (~645.5 mm and 471.2mm). In essense, their >> rainfall model >> and thus their modelled rainfall time series are no longer relevant to >> Sahel rainfall! >> >> I have seen many bad papers, but this one is the worst of all, not only >> because they >> misled the reader with their model (intentionally or unintentionally), >> but also because they >> made all kinds of unfounded pure speculations about the implications of >> their results. >> >> I did some quick analyses using data extracted from the update GHVN2 and >> wrote a >> comment paper, which is attached as Word file. Any comments will be >> appreciated. >> >> Regards, >> >> Aiguo >> >> Phil Jones wrote: >> >>> >>> Dear All, >>> Several emails today. Kevin's encouraging Aiguo Dai to write a >>> response as well, >>> so it might be worth some co-ordination. 2 responses might be better >>> than one, though, so I'll >>> leave it up to you. >>> They have dug themselves into a bigger hole in their response to >>> Joe. Joe's assessment >>> of their reasoning is exactly right. Also you can't write a paper >>> saying an analysis is flawed and >>> then say we don't dispute the local evidence for drought ! This is >>> naive in the extreme and >>> dumb. I've heard this excuse several times in the past with other >>> contentious papers. >>> The one problem there might be in a response is getting a quick >>> turnaround with IJC. >>> With the response a strongly worded letter should go to the editor >>> (Glenn McGregor) >>> requesting a fast-track review. The journal does this. As Kevin says >>> any response short >>> be short and to the point. >>> >>> Cheers >>> Phil >>> >>> >>> At 18:17 06/05/2004 -0400, Joseph M. Prospero wrote: >>> >>>> From: "A.Chappell" >>>> To: "Joseph M. Prospero" >>>> Cc: "Clive Agnew" >>>> Subject: Re: Sahel drought "artifact" >>>> Date: Tue, 13 Apr 2004 12:13:48 +0100 >>>> >>>> Dear Professor Prospero, >>>> >>>> Thank you for your email. I read your paper with interest. It does >>>> indeed show a strong correlation with conventional estimates of mean >>>> annual rainfall. However, the paper implicitly assumes that the >>>> mean annual rainfall represents the variation in rainfall for the >>>> entire region. Our paper shows that those statistics are flawed >>>> because of the changing station networks and that those regional >>>> statistics do not show a 'drought' in the Sahel. Our paper does not >>>> dispute the local scale evidence for drought. >>>> >>>> It is too simplistic to average mean monthly rainfall for such a >>>> large heterogenous region and believe that the rainfall trend is >>>> precise. What might be interesting is to correlate your results >>>> against the mean annual rainfall corrected for the changing station >>>> networks. >>>> >>>> Regards, >>>> >>>> Adrian >>>> >>>> >>>> >>>> ----- Original Message ----- >>>> From: Joseph M. Prospero To: >>>> a.chappell@salford.ac.uk >>>> Sent: Thursday, April 08, 2004 10:33 PM >>>> Subject: Sahel drought "artifact" >>>> >>> 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 p.jones@uea.ac.uk >>> NR4 7TJ >>> UK >>> >>> ---------------------------------------------------------------------------- >>> >>> >>> >>> >> >> -- >> Aiguo Dai email: adai@ucar.edu >> Climate & Global Dynamics Division phone: 303-497-1357 >> National Center for Atmospheric Research FAX : 303-497-1333 >> P.O. Box 3000, 1850 Table Mesa Drive >> Boulder, CO 80307 >> homepage: http://www.cgd.ucar.edu/cas/adai/ >> >>