4. Crisis de reconfiguración extractivista en el siglo XXI
4.4 Ejercicio de la violencia: “Nuevo imperialismo” en la minería
With an increase in the water vapour content, rainfall intensity will increase. This will lead to more floods and droughts (Burke et al., 2006). Extreme rainfall events will become more fre- quent than they are now. However, there may be longer intervals between (non-extreme) indivi - dual rain fall events. Climate model projections suggest future increases in precipitation, more intense rainfall, more droughts, and in general wet regions getting wetter, and dry regions becom - ing drier (IPCC 2007a, Figure 2.17). This leads to an increase in flood risk, which will pressure physical infrastructure and impact upon water quality. IPCC (2007b) estimates that 20% of the world population will live in areas with increasing river flood risk by the 2080s.
Regionally, the tropics and high latitudes are expected to get wetter, the sub-tropics drier (i.e. enhanced precipitation–evapotranspiration
deficit), with a poleward extension of the sub- tropics in both hemispheres (impacting upon the Mediterranean, South Australia, southwest USA). In mid-latitudes, changes in the seasonality of precipitation are expected, with drier sum- mers (likely to impact upon agriculture and wild - fire frequency and severity), and wetter winters (impli cations for flooding). Models project en - hancements in the East African monsoon and summer monsoons in South and South East Asia.
Figure 2.16 Schematic showing example feedbacks of enhanced water vapour in the atmosphere.
Figure 2.17 Robust findings on regional climate change for mean and extreme precipitation, drought and snow.
Source: From Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Box 11.1, Figure 2. Cambridge University Press.
The main uncertainty in precipitation predictions among climate models is at the boundary of these climate zones.
Another important consideration is whether the precipitation falls as rain or snow. With warming, the balance shifts to relatively more rain (consequently more river runoff) and earlier snowpack melt, and a general contraction of snow coverage. Snow effectively acts as freshwater storage, reducing seasonality in water input into soils, and reducing wintertime runoff losses. This is likely to have significant implications for soil moisture content and freshwater availability in spring and summertime, for example, increased requirements for crop irrigation. With global warming, water supplies from glaciers and snow are projected to decrease, reducing water avail - ability in regions dependent on glacier and snow melt. For South Asia this translates into a future decrease in mean water supply of –8.4%, –17.6%, and –19.6% for the upper Indus, Ganges, and Brahmaputra, respectively, despite consideration of the partial offsets from projected increases in monsoon rains (Immerzeel et al., 2010). Accounting for irrigation requirements for crops and population, the Brahmaputra and Indus basins are most susceptible to future decreased flows, putting an estimated 60 million people at risk of food insecurity (Immerzeel et al., 2010). Warming is likely to decrease permafrost (see Chapter 1) extent, challenging infrastructure in affected regions (ACIA, 2004). IPCC AR4 projects permafrost area to decrease by 20–35% by the mid-twenty-first century, and seasonal thaw depth to decrease by 30–50% by 2080.
The combined effects of future increases in precipitation with the competing effects of CO2
on plant physiology and warming acting to decrease and increase transpiration, respectively, lead to projections of increased river runoff (Betts et al., 2007). The IPCC Assessment Report 4, Working Group II, Chapter 3, ‘Freshwater resources and their management’, includes the following statements in the executive summary (IPCC, 2007b):
• Future river discharge will increase by 10 to 40% by mid-century at higher latitudes and in some wet tropical areas; decrease by 10 to 30% over some dry regions at mid-latitudes and dry tropics, due to decreases in rainfall and higher rates of evapotranspiration.
• Many semi-arid areas (e.g. the Mediterranean Basin, western United States, southern Africa and north-eastern Brazil) will suffer a decrease in water resources due to climate change. • The negative impacts of climate change
on freshwater systems outweigh its benefits. Increased annual runoff in some areas but increased precipitation variability and seas onal runoff shifts on water supply, water quality and flood risk.
• Increased temperatures will further affect the physical, chemical and biological properties of freshwater lakes and rivers, with predom - inantly adverse impacts on many individual freshwater species, community composition and water quality.
Uncertainties in the magnitude of future climate change relate to uncertainties in future population growth and socio-economic projec - tions, and differences in climate model sensitivity to fossil fuel emissions. The latter relates to uncertainties in the strength of feedbacks in the climate system. Also, although all climate models predict a future increase in global precipitation with warming, there is less consensus on the specific location of precipitation changes, not only the magnitude but even the sign of change differing among models (see Figure 2.17). Pro - jections of future land use and land cover changes vary markedly (Sitch et al., 2005) and, together with uncertainty in changes in water demand and climate change, these provide major challenges for future water cycle and freshwater security assessments.
F SUMMARY
The global water cycle is intimately linked to energy balance and transfers across the Earth for a number of reasons, including the latent heat transfer processes associated with evaporation and condensation and the fact that water vapour is an important greenhouse gas. There are large uncertainties in the estimates of the amounts of water being stored and transferred in parts of the global water cycle. There are also large variations between years, between inter-annual periods (e.g.
due to ENSO), and between decadal periods (e.g. due to aerosols and land use change). Future changes in climate, land use, and water demand are likely to profoundly affect the global water cycle. There are multiple positive and negative feedbacks operating between factors such as increased CO2 and plant physiology, aerosols,
temperature, precipitation and evapotrans pira - tion, changes in sea surface temperatures and atmospheric circulation patterns. The IPCC (2007b) report projects an intensification of the global water cycle, with future increases in precipitation and evaporation, and more intense rainfall, yet more droughts. Wet regions will get wetter and dry regions will get drier. The impacts of climate change include increases in annual river runoff, with changes in the seasonality of runoff in snow- and glacier-fed river basins, with implications for freshwater supply and food security for human populations and biodiversity. REFLECTIVE
QUESTION
What are the major changes to the water cycle that you would expect to see in the next 50–100 years as a result of climate change?
Look at the latest IPCC reports available online for the latest scientific reports on climate change impacts on the water cycle: http://www.ipcc.ch/ publications_and_data/publications_and_data_ reports.shtml.
Classic papers
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Held, I.M. and Soden, B.J. 2006. Robust responses of the hydrological cycle to global warming. Journal of
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The authors compare results from many models to see where the models agree that there are likely to be strong changes in the water cycle in the future. Roderick, M.L. and Farquhar, G.D. 2002. The cause of
decreased pan evaporation over the past 50 years.
Science 298: 1410–1411.
Another example of a feedback effect – here increased cloud cover and aerosols are shown to be linked to reduced measured evaporation. FURTHER READING
n Using data in Figure 2.1 and using a bucket of water to represent all of the water on Earth,
design a poster that shows how much water from the bucket would be found in different stores (riverflow, lakes, atmosphere, oceans, etc.).
PROJECT IDEAS
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n Produce a list of extreme events that have impacted upon the water cycle in your region
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A INTRODUCTION
The way water moves across and through a landscape is very important for determining river flow, water quality, and even the evolution of landscapes themselves. It is common to try to understand water movements across landscapes within topographically confined units. We call these units river basins (also known as water - shedsor catchments), which are defined by the upslope area draining into a given point on a river. These can vary in scale from hillslopes to the size of the Amazon basin at 6 160 000 km2.
While the Amazon’s seemingly vast river basin area amounts to only 2% of the Earth’s land mass, the Amazon carries around one-fifth of the world’s annual river discharge because the
majority of its area rests in a tropical region with plentiful rainfall.
It is possible to create a water budget for a river basin, whereby we try to measure the inputs, outputs and stores of water for the system and understand how efficient the system is at turning rainfall into river flow. Depending on the environ - mental conditions, almost 100% of precipitation may reach the river, or as a little as zero. The rate at which water is delivered to the ground surface and the pathways and speed at which water travels across and through a land scape may also be impacted upon by climate change and land man age ment activity, and these factors may affect flood risk. It is therefore important to understand the flow pathways for water across river basins and how environmental change may CHAPTER THREE