FLOOD06027

• County: Statewide
• Basin: Statewide
• Title: Of Carts and Horses in Hydrologic Modeling
• Date: 4/1/1997
• Floodplain - Doc Type: Educational/Technical/Reference Information

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GUEST EDITORIAL

tEI/15H

OF CARTS AND HORSES IN HYDROLOGIC
MODELING

Historical Perspective

Hydrologic modeling is a relatively new concept and some-
times only a more impressive label for what used to be called
"methods of hydrological computations" until the 19608.
Thus, one would search in vain for "hydrologic models" in
such applied-hydrology classics as Linsley et al. (1949, 1958).
Even the famous Handbook of Applied Hydrology (Chow
1964) mentions the term "hydrologic model" in only one
fourth-order heading in the context of statistical and probabi-
listic data analysis-indeed, the only sentence explicitly re-
ferring to hydrologic models that I could find in this
monumental volume is this: "Hydrologic models considered
here are mathematical formulations to simulate natural hydro-
logic phenomena which are considered as processes or as sys-
tems."
And that is what they are or at least what they are meant
to be: mathematical models of hydrologic processes or sys-
tems.
The "upgrading" of "computational methodsu to "math-
ematical models" was brought about by the advent of the
computer and the consequent "mathematization" of many
kinds of analytical and technical work. This produced a burst
of activity in mathematically literate university departments
such as engineering: computer-based mathematical modeling
made attractive to them previously uninteresting empirical dis-
ciplines that had low mathematical content and relied heavily
on manual execution of various numerical and graphical tech-
niques. Such disciplines had evolved from practical needs of
various professions, remained largely within their domain of
interest, and, in the academic environment, were relegated to
the fringes of scientifically more respectable fields.
Hydrology was, of course, a prime example of such empir-
ical disciplines, having evolved chiefly from hydraulic engi-
neering and its need for hydrology-related design parameters
and operational characteristics of various water resource
projects. Here I am deliberately using the term "discipline"
because even today hydrology is only slowly asserting itself
as a science in its own right. These topics were discussed in
greater detail elsewhere (Kleme~ 1986, 1988).
For hydrology as a science, the invasion of mathematical
modeling was nothing short of a disaster. It has retarded rather
than advanced the development of hydrology because, with
very few exceptions, it focussed all efforts on polishing the
mathematical and computational aspects of methods and tech-
niques, leaving the understanding of the substance at the 1930s
level, where it had been brought by the old guard of profes-
sionals like Hazen, Sherman, Horton, Theis, to name a few.
Even this is an overly optimistic assessment of the actual sit-
uation. In reality, while this limited and fragmented hydrolog-
ical knowledge did exist, it was often deliberately ignored and
avoided by the new generation of modelers. Out of enthusi-
astic naivety or calculated self-interest, they flaunted their hy-
drological ignorance as "absence of bias" and believed (some
still do) that the mathematical rigor of models and the close-
ness of their fit to empirical data are the supreme guarantors
of scientific objectivity and the key to true and reliable hydro-
logic understanding.
The contrast between the new and the old could not be
sharper. The focus of the old guard was the substance and its
hydrology was usually right, though sometimes the mathe-
matics was not. The focus of the new generation of modelers
has been the, form: the mathematics is usually correct and it
would be a compliment to say the hydrology is sometimes

wrong-more often it is totally absent. One is reminded here
of a comment physicist Niels Bohr is supposed to have made
to one of his students: "This is not right , , . This is not even
wronglY'
Hydrological discoveries of the old school invariably were
the product of extensive personal involvement of its authors
in practical hydrological work related to water resource engi-
neering projects. Their papers have the unmistakable imprint
of mature professionals going seriously about their business
and, in the process, getting ideas on how the current practice
of their profession could be improved, One can see that these
people were not playing games.
On the other hand, this is exactly the impression one gets
from reading papers of the academic hydrologic modelers of
the new generation. While most,of them have engineering de-
grees, they have never practiced engineering and, while pos-
turing as hydrologists, they have, for the most part, never se-
riously studied or practiced hydrology either. As I once
characterized a typical academic hydrologic modeler: "Sus-
pended between a technology he does not practice and a sci-
ence for which he has not been trained, his 'research' is 'nat-
urally guided to performing elaborate pirouettes on the high
wire of techniques connecting the distant poles and holding
him in place" (Kleme~ 1988a). '
Having come to hydrology after practicing water resources
engineering for more than a decade, during which I gradually
realized how little hydrology I knew and how important its
knowledge was, I was eager to drink from the fountain of
hydrologic knowledge I thought must be hidden behind the
intimidating jargon and algebra-all those convolutions, La-
guerre functions, fractional and other noises, and so on. Alas,
there was no fountain, only sterile desert! After a dozen years
of exposure to practical hydrological problems and participa-
tion in neck-breaking decisions on multimillion investments
made with the knowledge of the large hydrological uncertain-
ties involved, I was literally insulted when I realized that ,all
what this high-power prestidigitation, posturing as "scientific
hydrology," can teach me is how to fit a line to a few points,
extrapolate a curve by the most abstruse and esoteric means
available, and keep calibrating (i.e., fudging) an arbitrary sys-
tem with an excessive number of the degrees of freedom until
it fits some hydrologic record.
I soon made my displeasure known, deploring "the empha-
sis ,.. on the fitting of various preconceived mathematical
models to empirical data rather than on arriving at a proper
model from the physical nature of the process itself," warning
that "such approach can hardly contribute to hydrological
knowledge," drawing attention "to the fact that inferences
about physical features of a process, based on operational
models, can be not only inaccurate but grossly misleading"
(Kleme~ 1974), and pointing out the various malignant facets
of the misguided practices ever since (Kleme~ 1978, 1982,
1986, 1987, 1988a, 1991, 1994, 1995). However, if this per-
sistence looks like a paranoic obsession, I may say in my de-
fense that, except for the 1974 "Hurst phenomenon" paper,
all the other papers cited were written based on invitations.
This editorial is an elaboration of the argument sketched in
(K1emd 1995). It was written at the suggestion of the editor
of this journal, who has assured me that the message still is
, by no means obsolete.

Diagnosing the Problem

There are many causes for the regrettable state in which the
mainstream of hydrologic modeling has been meandering for
the past 30 years or so. They fall into two broad categories
that can be labeled as "scientific" and "socioeconomic,"

JOURNAL OF HYDROLOGIC ENGINEERING I APRIL 1997/43