Impatti, adattamento e vulnerabilita Le cause e le responsabilita dei cambiamenti climatici sono state trattate sul numero di ottobre della rivista Cda. Approfondiamo l’argomento presentando il documento: “Cambiamenti climatici 2007: impatti, adattamento e vulnerabilita” votato ad aprile 2007 dal secondo gruppo di lavoro del Comitato Intergovernativo sui Cambiamenti Climatici (Intergovernmental Panel on Climate Change). Si tratta del secondo di tre documenti che compongono il quarto rapporto sui cambiamenti climatici.

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Climate Change 2007: Impacts, Adaptation and Vulnerability.

Arsenic-contaminated groundwater used for drinking in China is a health threat that was first recognized in the 1960s. However, because of the sheer size of the country, millions of groundwater wells remain to be tested in order to determine the magnitude of the problem. We developed a statistical risk model that classifies safe and unsafe areas with respect to geogenic arsenic contamination in China, using the threshold of 10 micrograms per liter, the World Health Organization guideline and current Chinese standard for drinking water. We estimate that 19.6 million people are at risk of being affected by the consumption of arsenic-contaminated groundwater. Although the results must be confirmed with additional field measurements, our risk model identifies numerous arsenic-affected areas and highlights the potential magnitude of this health threat in China.

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Groundwater Arsenic Contamination Throughout China

Recent developments in the direct-current geoelectrical imaging method

The repercussions of climate change will be felt in various ways throughout both natural and human systems in Sub-Saharan Africa. Climate change projections for this region point to a warming trend, particularly in the inland subtropics; frequent occurrence of extreme heat events; increasing aridity; and changes in rainfall—with a particularly pronounced decline in southern Africa and an increase in East Africa. The region could also experience as much as one meter of sea-level rise by the end of this century under a 4 °C warming scenario. Sub-Saharan Africa’s already high rates of undernutrition and infectious disease can be expected to increase compared to a scenario without climate change. Particularly vulnerable to these climatic changes are the rainfed agricultural systems on which the livelihoods of a large proportion of the region’s population currently depend. As agricultural livelihoods become more precarious, the rate of rural–urban migration may be expected to grow, adding to the already significant urbanization trend in the region. The movement of people into informal settlements may expose them to a variety of risks different but no less serious than those faced in their place of origin, including outbreaks of infectious disease, flash flooding and food price increases. Impacts across sectors are likely to amplify the overall effect but remain little understood.

Climate change impacts in Sub-Saharan Africa: from physical changes to their social repercussions

In Africa, groundwater is the major source of drinking water and its use for irrigation is forecast to increase substantially to combat growing food insecurity. Despite this, there is little quantitative information on groundwater resources in Africa, and groundwater storage is consequently omitted from assessments of freshwater availability. Here we present the first quantitative continent-wide maps of aquifer storage and potential borehole yields in Africa based on an extensive review of available maps, publications and data. We estimate total groundwater storage in Africa to be 0.66 million km 3 (0.36‐1.75 million km 3 ). Not all of this groundwater storage is available for abstraction, but the estimated volume is more than 100 times estimates of annual renewable freshwater resources on Africa. Groundwater resources are unevenly distributed: the largest groundwater volumes are found in the large sedimentary aquifers in the North African countries Libya, Algeria, Egypt and Sudan. Nevertheless, for many African countries appropriately sited and constructed boreholes can support handpump

/pdf/quantitative-maps-of-groundwater-resources-in-africa-4pikje9261.pdf

Quantitative maps of groundwater resources in Africa

One of the key uncertainties surrounding the impacts of climate change in Africa is the effect on the sustainability of rural water supplies. Many of these water supplies abstract from shallow groundwater (<50 m) and are the sole source of safe drinking water for rural populations. Analysis of existing rainfall and recharge studies suggests that climate change is unlikely to lead to widespread catastrophic failure of improved rural groundwater supplies. These require only 10 mm of recharge annually per year to support a hand pump, which should still be achievable for much of the continent, although up to 90 million people may be affected in marginal groundwater recharge areas (200–500 mm annual rainfall). Lessons learnt from groundwater source behaviour during recent droughts, substantiated by groundwater modelling, indicate that increased demand on dispersed water points, as shallow unimproved sources progressively fail, poses a much greater risk of individual source failure than regional resource depletion. Low yielding sources in poor aquifers are most at risk. Predicted increased rainfall intensity may also increase the risk of contamination of very shallow groundwater. Looking to the future, an increase in major groundwater-based irrigation systems, as food prices rise and surface water becomes more unreliable, may threaten long-term sustainability as competition for groundwater increases. To help prepare for increased climate variability, it is essential to understand the balance between water availability, access to water, and use/demand. In practice, this means increasing access to secure domestic water, understanding and mapping renewable and non-renewable groundwater resources, promoting small-scale irrigation and widening the scope of early warning systems and mapping to include access to water.

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What impact will climate change have on rural groundwater supplies in Africa

Manganese concentrations in Scottish groundwater.

This report describes how the BGS Permeability Index dataset has been prepared and includes
guidance on how it can be used. It discusses what the indices mean and how the data have
been derived. It describes the methodology used to classify each geological unit in the Digital
Geological Map of Great Britain at 1:50 000 scale (DiGMapGB-50) according to its
predominant flow type and probable permeability.
The Permeability Index is a qualitative classification of estimated rates of vertical movement
of water from the ground surface through the unsaturated zone, the zone between the land
surface and the water table. The Permeability Index codes have been allocated to every
lithology (or combination of lithologies) for each named rock unit that has been mapped in
DiGMapGB-50. This has been carried out for all four types of deposit shown as separate
layers in the DiGMapGB-50 (artificial ground, mass movement deposits, superficial deposits
and bedrock) dataset.
The Permeability Index consists of a three-part code representing:
• Predominant Flow Mechanism
• Maximum Permeability
• Minimum Permeability
The Predominant Flow Mechanism code indicates how fluid will migrate from the ground
surface through the unsaturated zone of each rock unit and lithology combination and has
three classes, intergranular, fracture or mixed (intergranular and fracture).
The second and third codes (Maximum and Minimum Permeability) indicate the range of
flow rates likely to be encountered in the unsaturated zone for each rock unit and lithology
combination. Five classes have been used for the Maximum and Minimum Permeability
codes: very high, high, moderate, low and very low. The Maximum and Minimum
Permeability values represent a likely permeability range for the specific named rock unit and
lithology combination at, and immediately below, outcrop (rather than at any significant
depth).
The Maximum Permeability represents the fastest potential vertical rate of migration through
the unsaturated zone likely to be encountered. The Minimum Permeability represents the
minimum, and in some cases more normal, bulk rate of vertical movement likely to be
encountered. Where a widely variable lithology combination occurs within a rock unit this
value reflects the probable movement rate likely to be encountered in the least permeable
horizons
The coding was based on expert judgement but with the following assumptions:
• the lithological component(s) for a particular named rock unit mapped within
DiGMapGB-50 was correct, whether or not this was expected or normal for the given
formation.
• the order of the deposits in a lithological ‘string’ was of relevance; it was assumed that
the dominant lithology was placed first, with the other lithologies in order of their
occurrence, e.g. gravel, sand, silt and clay was different to, and more permeable than,
clay, silt, sand and gravel.
• that all of the possible geological layers (artificial, mass movement, superficial
deposits and bedrock) that could be present at a site were mapped. It is, however, known that this is not the case where the maps are old and the presence of superficial
deposits was not always recorded. Similarly the presence of artificial deposits is
constantly changing and only those present at the time of survey were recorded

/pdf/guide-to-permeability-indices-ph5vesnc7e.pdf

Guide to Permeability Indices

In many areas throughout Africa, a staggering proportion of
wells and boreholes fail. Failure can occur for a number of
reasons – inadequate maintenance and community
involvement, poor engineering or a lack of water. Often it
can be difficult to work out the exact reason after the event.

However, in many geological environments the impacts of
poorly sited and designed boreholes and wells are a major
concern to funding agencies, implementing institutions and
local communities. In such areas, good supplies of
groundwater cannot be found everywhere, and boreholes
and wells must be sited and designed carefully to make use
of the available groundwater. To appropriately site and
design water sources, the groundwater resources of an area
need first to be investigated to understand how water occurs
in the ground.

In this manual we present some techniques that allow a
quick assessment of groundwater resources without
requiring much expertise or expense. Some of the
techniques are old and established while others are new.
However, all techniques have been tested by BGS (and
others) in assessing groundwater resources in Africa. This
manual does not claim to be a detailed textbook for
hydrogeologists – there are enough already (see reading list
at the end of the chapter). Rather it is meant as a practicalaid for those involved in the practice of rural water supply, particularly in Africa. Little training or equipment is required for the tests and they can all be carried out in a short space of time.

The manual is divided into six sections. The first gives
an overview of the groundwater resources of sub-Saharan
Africa (SSA) and discusses the scope and detail of
investigations required in different geological
environments. The remaining chapters describe simple
techniques for assessing groundwater resources, from basic
reconnaissance to assessing the yield of a borehole. In the
appendix are summary sheets of the most common
techniques which can be photocopied and used in the field.

Simple methods for assessing groundwater resources in low permeability areas of Africa

Groundwater provides most of the domestic water supply in rural Africa and supports
poverty reduction through irrigation. Climate change along with rapid population growth are
likely to impact all water resources, but the response of groundwater will be slower than that
of surface water. This could provide a potential buffer to support adaptation strategies. A key
advantage of groundwater is its reliability: aquifer storage ensures that groundwater supplies
can be maintained during periods of little or no rainfall and help to even out meteorological
variability. As a natural store of water, aquifer storage is many orders of magnitude greater
than that which can be achieved through constructing surface water reservoirs.
The IPCC Fourth Assessment report review of climate model projections shows a
consistent pattern of progressive warming of the climate in all regions of Africa, but a much
less consistent pattern for rainfall (Solomon et al. 2007). The increased temperature will
lead to higher rates of evapotranspiration and likely increase in the intensity and variability
of rainfall (Conway 2011). Although the exact impact on runoff and groundwater recharge
is unclear, most scientists agree that both will become less reliable.
Making more use of groundwater will therefore be critical in helping communities and
countries adapt and build resilience to changes in climate. This is likely to include the
increasing use of groundwater for both small-scale household/village irrigation and largerscale
commercial irrigation; and increased use of motorized borehole pumps for reliable
urban water supply (small towns to larger conurbations).
The benefits of groundwater are well recognised (MacDonald et al. 2005), but there is limited
knowledge of African groundwater resources and how they might respond to changes in
climate. There has been little systematic assessment of groundwater storage and availability
which was reflected in the paucity of information on groundwater presented in the IPCC
Fourth Assessment Report and Technical Paper on Water, where there was major uncertainty
as to how changes in climate may affect groundwater (Solomon et al. 2007; Bates et al. 2008).

http://r4d.dfid.gov.uk/PDF/Outputs/Misc_Env/60826_AfricaGWresilience_ResearchSummary_Sept2011.pdf

Brighid O Dochartaigh

Papers

What impact will climate change have on rural groundwater supplies in Africa

Manganese concentrations in Scottish groundwater.

Guide to Permeability Indices

Simple methods for assessing groundwater resources in low permeability areas of Africa

Groundwater resilience to climate change in Africa