Geology Reference
In-Depth Information
designing a modelling strategy. The fourth
assessment report of the Intergovernmental
Panel for Climate Change (IPCC) (Parry
et al
.,
2007; Solomon
et al
., 2007) reviews a number
of potential changes to soil erosion drivers
and processes. This chapter summarizes these
impacts as changes to rainfall erosivity, water
runoff, vegetation cover and soil erodibility,
with a focus on the combined changes caused by
desertification.
cipitation intensity emerging from model results,
although with a high regional, interannual and
inter-model variability. The largest and most sig-
nificant changes were found in days with rainfall
over 10 mm, and 5-day maximum rainfall, which
indicate more precipitation for a given event,
resulting from the greater moisture-holding
capacity of a warmer atmosphere and a polewards
shift of storm tracks. Precipitation intensity is
expected to increase over all land masses, with
significant increases in the mid to high latitudes
of the northern hemisphere and the tropical
regions of Africa and South America. In the sub-
tropical regions, an increase in the number of dry
days is coupled with no significant changes to
rainfall intensity.
Climate change projections from GCMs
should be treated with care, since the non-linear
nature of the climate system and natural forc-
ings, compounded with differences in the for-
mulation of different GCMs, causes an intrinsic
level of uncertainty in GCM-based climate
change predictions (Stott & Kettleborough,
2002; Giorgi, 2005). Nevertheless, the consist-
ency of the predictions among the GCMs as well
as with the historical climate record indicates
that rainfall erosivity will increase in many
regions throughout the globe. Ongoing research
focusing on regional climate change predictions
and climate extremes (e.g. Hanson
et al
., 2007)
should provide better estimates of the impacts
of climate change on rainfall erosivity in the
near future.
15.2.1 Rainfall erosivity
One of the most direct impacts of climate change
could be an increase in the erosive power of
rainfall. In the IPCC's fourth assessment report,
Meehl
et al
. (2007) reported that global general
circulation models (GCMs) point to an average
increase in rainfall of 5% over land masses by
2100, but unevenly distributed, with the high
latitudes, the tropics and the monsoon region of
southeast Asia experiencing the highest increases
(up to +20%) and with the largest decreases over
the Caribbean and Mediterranean seas and in the
western subtropical coasts of each continent
(down to −20%). Rainfall increases are expected to
reflect disproportionately in heavy precipitation
events, with average rainfall intensity increasing,
which is also a trend that has been observed in
the global climate record (Groisman
et al
., 2005;
Trenberth
et al
., 2007). Even in regions where
rainfall decreases, this is expected to lead to an
increase in the length of dry periods, with rainfall
intensity in wet periods increasing; in some of
these regions this fact could be particularly
significant due to the contribution of rare extreme
events for overall soil erosion (e.g. González-
Hidalgo
et al
., 2007). Finally, rainfall increases
could accumulate with a shift from snowfall to
rainfall due to the warmer climate (Kundzewicz
et al
., 2007).
As an example of current climate change sce-
narios for extreme events, Tebaldi
et al
. (2006)
analysed historical and future simulations of
precipitation extremes indicators by nine GCMs,
under a range of emission scenarios. The authors
reported a significant global trend of greater pre-
15.2.2 Water runoff
The estimated impacts of climate change on run-
off are more complex than on rainfall. The IPCC's
fourth assessment report (Kundzewicz
et al
.,
2007) points to significant changes in river run-
off, due to changes in rainfall coupled with an
increase in potential evapotranspiration, as higher
temperatures increase the atmospheric vapour
pressure deficit. Changes to runoff are generally
expected to follow changes in rainfall, increasing
in high latitudes, southeast Asia and the tropics
(where rainfall is expected to increase more than
