Geoscience Reference
In-Depth Information
extreme weather conditions are projected to affect availabil-
ity and distribution of rainfall, snow melting, river flows and
ground water. Water stress is already high, particularly in many
developing countries. Water resources management affects
almost all aspects of society and the economy, in particular
health, food production and food security, domestic water sup-
ply and sanitation, health, energy, industry, ecosystem function
and environmental sustainability (IPCC, 2007).
Changes in rainfall due to global climate change may effect
the surface moisture availability, which becomes important for
crop stand establishment in the rain-fed areas. Modelling tech-
niques are not reliable enough to predict precipitation changes
and one can expect some increased drought in some regions
and increased rainfall in others. Small changes in precipitation
can have magnified run-off effects. Doubling of CO
2
predicts
a 8-15% increase in global precipitation with a 30% increase
in the water-holding capacity, but the atmosphere precipita-
tion will not keep up with potential evaporation. The problem
will be more acute at higher altitudes. Run-off is also likely
to decrease due to more arid conditions and the increased fre-
quency of droughts.
15.9
Climate change and soil fertility
Soil fertility is very essential for sustaining productivity in
the world and depends on a complex network of soil struc-
ture, water, oxygen and nutrient availability. The soil's organic
matter enables it to support plant life and soil microbes. Soil
microbes facilitate the decomposition of organic matter from
litter fall and CO
2
is a natural by-product of this process.
Rising atmospheric temperatures and/or CO
2
levels are likely
to increase photosynthesis and plant productivity. However, the
effects of warming on soil's molecular composition have been
poorly studied. It is therefore unclear to what extent the car-
bon-containing components of soil matter will accumulate or
degrade and thus how much carbon will be sequestered by the
soil and how much will be released into the atmosphere as CO
2
.
The doubling of CO
2
increases plant biomass production,
soil water use efficiency by the plants and C/N ratios of plants.
The change in the C/N ratios of plant residues returned to the
soil have impact on soil microbial processes and affects the pro-
duction of trace gases NO
x
and N
2
O. Higher soil temperature
stimulates microbial respiration and decomposition of organic
matter. Plants may take in more nutrients. Brackish-water
