Geoscience Reference
In-Depth Information
peratures. This increased probability of drought will have all sorts of knock-on effects for
the forest ecosystems and the rivers running through them, including a greater likelihood
of fire. The consequences for local people, wildlife, and the rivers themselves are expected
to be serious.
In Europe, the discharge of the Rhine is expected to become more seasonal because of glob-
al warming. Estimates generated by computer models indicate that by 2050, the average
flow in summer will decrease by up to 45% and the average winter flow will increase by up
to 30%. Less water in the Rhine during the summer months is related mainly to predicted
decreases in precipitation and increases in evapotranspiration. Greater flows in winter will
be caused by a combination of more precipitation, less snow storage, and increased early
melting. The hazards posed by winter floods on the Rhine will certainly increase in conse-
quence. Greater seasonality in the river's flow will also have numerous repercussions for
the ecology of the Rhine.
River restoration
The numerous ways in which human activities have influenced rivers, both purposefully
and indirectly, are complemented in many countries by efforts to reverse some of the earlier
effects of human action: so-called 'river restoration'. Attempts to improve conditions in
rivers are not new in themselves, as evidenced in the clean-up of the Thames in London
cited earlier in this chapter, for instance, but the widespread adoption of restoration, re-
habilitation, and mitigation measures has been recognized as a distinctive phase of river
management in the late 20th and early 21st centuries. Restoration projects usually involve
efforts to repair damage to rivers, typically in an attempt to better meet societies' needs and
expectations for natural, ecologically healthy waterways.
Returning a river to its 'natural' or 'original' condition is usually fraught with difficulty,
however. Theoretically, at least, this can be based on an understanding of historical condi-
tions along a river before human effects, or on conditions along a similar but less affected
reference river. In practice, however, an appropriate reference river may not exist, or condi-
tions in a basin (such as climate or vegetation) may have changed since the period selected
for the historical baseline. Indeed, rivers change under all sorts of natural circumstances,
and determining which changes are natural and which are due to human pressures is not
always straightforward. Further, although it may be possible to determine which human
impacts are undesirable, preventing them entirely may be more complicated.
