Introduction - Runoff Prediction in Ungauged Basins: Synthesis across Processes, Places and Scales - page 5

collective understanding in hydrology, just as the six blind
men in the Indian legend might have joined forces to
enlighten themselves about the elephant to seek wisdom
from other sources. The PUB initiative has been guided by
a number of overarching principles to help reach its goals
( Figure 1.4 ). First and foremost, the initiative was about
real hydrological processes in real catchments, embracing
a multitude of processes, places and scales. If real progress
was to be made in overcoming the fragmentation, a diverse
population of real catchments in different regions and at
different scales had to be examined. A diverse range of
processes and a diverse range of data and approaches
had to be brought together, all focusing on the common
science problem of predictions in ungauged basins. By
making different catchments and methods comparable,
the aim was to synthesise existing knowledge and create
new knowledge, and in this way help improve the predict-
ive abilities and reduce uncertainty. Comparability of
diverse places, methods and applications was considered
the key to the unification or synthesis needed to transcend
the fragmentation and make fundamental progress in
hydrology.
It was thus clear that to overcome the fragmentation
the community had to be brought together. The PUB
initiative was therefore designed as a global community
effort, indeed a grassroots movement, consisting of a
network of scientists from around the world, and inclu-
sive of all interests. A balance of researchers interested
in fundamental research as well as in what is immedi-
ately useful was considered valuable, as for any other
relevant facets of the prediction problem. The benefits to
be gained were clear: greater coherence of the science
agenda, coordination of the research activities and a
stimulus for the excitement of hydrological research.
The PUB initiative has been a truly international effort,
with contributors from every continent focusing on the
issue of predictions in ungauged basins, leading to a
network of concerned scientists.
Over the past decade, the IAHS PUB initiative has been
the catalyst for a range of research activities organised
around six cross-cutting themes, and executed through a
large number of national, regional and global PUB
working groups. These PUB themes are: (i) catchment
similarity and classification, (ii) conceptualisation of pro-
cess heterogeneity, (iii) uncertainty analysis and model
diagnostics, (iv) new data collection approaches, (v) new
hydrological theory and (vi) new modelling approaches.
These themes are reflected in the frontispiece to this topic,
and figure prominently in the guide to PUB best practice
that appears in Chapter 13 (Recommendations). The PUB
research activities have contributed substantially to the
literature, leading to significant advances in the various
programs of PUB.

Figure 1.3. Fragmentation in hydrology: similar to the six blind
men, a fragmented approach to hydrology makes it difficult to
see the full pattern of catchment processes. From Sivapalan et al.
( 2003b ), © Jason Hunt.

touches the ear, and a rope to the one who touches the tail
( Figure 1.3 ). The experiences and interpretations of the six
blind men are different, which makes it difficult for them to
come up with a collective understanding and agree on the
true nature of the beast

they are trying to ' visualise ' .

A verse of John Godfrey Saxe 87) version of this

famous Indian legend clearly brings out this confusion:

' s (1816 -

And so these men of Indostan
Disputed loud and long,
Each in his own opinion
Exceeding stiff and strong,
Though each was partly in the right,
And all were in the wrong!

Perhaps catchment hydrology is in a similar state. Like the
six blind men, hydrologists too are often partly in the right
but they continue to fail to grasp the holistic picture of the
catchment, the object of their study. There is a clear and
urgent need to develop a unified vision of hydrology at the
catchment scale that overcomes the limitations that arise
from their narrow perspectives. What is needed is a syn-
thesis that helps to broaden their perspectives, and to go
beyond what is perceived by an individual researcher or
group.

1.4 The Prediction in Ungauged Basins initiative:
a response to the challenge of fragmentation
About a decade ago, a new global initiative was launched
by the hydrological community, under the aegis of the
International Association of Hydrological Sciences
(IAHS). Called Prediction in Ungauged Basins (PUB),
one of the motivations of this grassroots initiative was to
overcome the fragmentation in catchment hydrology (Siva-
palan et al., 2003b ; SSG, 2003 ). The idea was to bring the
scientific community together to use PUB to advance the