The pluvial debate - Climatic Change in Deserts - page 210

he considered that all geologists who failed to agree with him on this matter - at that
time the majority - should be afflicted with eternal itch without benefit of scratching.
The aim of this chapter is to consider how the concept of a pluvial climate first
arose and how it has at times led to spurious interpretations, provoking rebuttals and
subsequent more rigorous investigations, culminating in our present understanding of
the patterns of past climatic change in and around the deserts.
12.2 What is a pluvial?
In common usage, the adjective pluvial denotes rainy (from the seventeenth-century
Latin term pluvialis , itself derived from pluvia - the classical Latin word for rain). In
geologic usage, the noun pluvial often denotes a period of persistent, heavy rainfall
and was originally applied to lakes in arid or semi-arid areas that once occupied far
larger areas than their present-day remnants, whether they survive today as small
freshwater lakes, saline lakes or saltpans.
In The Encyclopaedic Dictionary of Physical Geography , Goudie ( 1985 , p. 339)
offers this expanded definition and note of caution:
Pluvial: Time of greater moisture availability, caused by increased precipitation and/or reduced
evaporation levels. Pluvials caused many lake levels in the arid and seasonally humid tropics
to be high at various times in the Pleistocene and early Holocene (hence pluvials may also be
called lacustrals), helped to recharge groundwater, and caused river systems to be integrated.
Pluvials used to be equated in a simple temporal manner with glacials, but this point of view
is no longer acceptable.
Goudie's definition hints at a number of possible problems when attempting to use
pluvial lakes to reconstruct past climates in presently dry areas. These issues may be
expressed as a series of questions to which we shall seek answers in this chapter. Was
the pluvial lake much larger than its modern counterpart because there was far more
precipitation in the lake basin at that time? Or was the lake bigger because there was
much less evaporation from the lake surface, perhaps related to lower temperatures,
at that time? Were the temperatures lower because the lakes were high during glacial
intervals, when summer temperatures would presumably have been far colder than
they are today? Was the last glacial climate wetter or drier than today? Or was it wet
in some regions and dry in others? Finally, how well dated are the lake sediments and
shorelines? Our concern here is to offer a brief review of the history of the changing
pluvial concept. This overview will serve as a coda to the more detailed discussion
in Chapter 11 in which we assessed the climatic insights to be derived from lakes in
now arid areas.
Before proceeding further, it will be helpful to define the term pluvial more rigor-
ously. Flint ( 1971 , p. 441) provided a comprehensive definition that meets our needs
admirably:
In an effort to approach precision, we shall take pluvial (noun or adjective) to mean a climatic
regimen of sufficient duration to be represented in the physical or organic record, and in which