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- Permanent Link:
- http://dpanther.fiu.edu/dpService/dpPurlService/purl/FI15042647/00001
Notes
- Abstract:
- Observational records and climate projections provide abundant evidence that freshwater resources
are vulnerable and have the potential to be strongly impacted by climate change, with wide-ranging
consequences for human societies and ecosystems.
Observed warming over several decades has been linked
to changes in the large-scale hydrological cycle such as:
increasing atmospheric water vapour content; changing
precipitation patterns, intensity and extremes; reduced snow
cover and widespread melting of ice; and changes in soil
moisture and runoff. Precipitation changes show substantial
spatial and inter-decadal variability. Over the 20th century,
precipitation has mostly increased over land in high northern
latitudes, while decreases have dominated from 10°S to 30°N
since the 1970s. The frequency of heavy precipitation events (or
proportion of total rainfall from heavy falls) has increased over
most areas (likely1). Globally, the area of land classified as very
dry has more than doubled since the 1970s (likely). There have
been significant decreases in water storage in mountain glaciers
and Northern Hemisphere snow cover. Shifts in the amplitude
and timing of runoff in glacier- and snowmelt-fed rivers, and in
ice-related phenomena in rivers and lakes, have been observed
(high confidence). [2.12]
Climate model simulations for the 21st century are consistent
in projecting precipitation increases in high latitudes (very
likely) and parts of the tropics, and decreases in some subtropical
and lower mid-latitude regions (likely). Outside
these areas, the sign and magnitude of projected changes
varies between models, leading to substantial uncertainty
in precipitation projections.3 Thus projections of future
precipitation changes are more robust for some regions than for
others. Projections become less consistent between models as
spatial scales decrease. [2.3.1]
By the middle of the 21st century, annual average river runoff
and water availability are projected to increase as a result of
climate change4 at high latitudes and in some wet tropical
areas, and decrease over some dry regions at mid-latitudes
and in the dry tropics.5 Many semi-arid and arid areas (e.g., the
Mediterranean Basin, western USA, southern Africa and northeastern
Brazil) are particularly exposed to the impacts of climate
change and are projected to suffer a decrease of water resources
due to climate change (high confidence). [2.3.6]
Increased precipitation intensity and variability are
projected to increase the risks of flooding and drought
in many areas. The frequency of heavy precipitation events
(or proportion of total rainfall from heavy falls) will be very
likely to increase over most areas during the 21st century, with
consequences for the risk of rain-generated floods. At the same
time, the proportion of land surface in extreme drought at any
one time is projected to increase (likely), in addition to a tendency
for drying in continental interiors during summer, especially in
the sub-tropics, low and mid-latitudes. [2.3.1, 3.2.1]
Water supplies stored in glaciers and snow cover are
projected to decline in the course of the century, thus
reducing water availability during warm and dry periods
(through a seasonal shift in streamflow, an increase in the
ratio of winter to annual flows, and reductions in low flows) in
regions supplied by melt water from major mountain ranges,
where more than one-sixth of the world’s population currently
live (high confidence). [2.1.2, 2.3.2, 2.3.6]
Higher water temperatures and changes in extremes,
including floods and droughts, are projected to affect water
quality and exacerbate many forms of water pollution –
from sediments, nutrients, dissolved organic carbon, pathogens,
pesticides and salt, as well as thermal pollution, with possible
negative impacts on ecosystems, human health, and water system
reliability and operating costs (high confidence). In addition,
sea-level rise is projected to extend areas of salinisation of
groundwater and estuaries, resulting in a decrease of freshwater
availability for humans and ecosystems in coastal areas.
[3.2.1.4, 4.4.3]
Globally, the negative impacts of future climate change on
freshwater systems are expected to outweigh the benefits
(high confidence). By the 2050s, the area of land subject to
increasing water stress due to climate change is projected to
be more than double that with decreasing water stress. Areas
in which runoff is projected to decline face a clear reduction in
the value of the services provided by water resources. Increased
annual runoff in some areas is projected to lead to increased
total water supply. However, in many regions, this benefit is
likely to be counterbalanced by the negative effects of increased
precipitation variability and seasonal runoff shifts in water
supply, water quality and flood risks (high confidence). [3.2.5]
Changes in water quantity and quality due to climate change
are expected to affect food availability, stability, access and
utilisation. This is expected to lead to decreased food security and
increased vulnerability of poor rural farmers, especially in the arid
and semi-arid tropics and Asian and African megadeltas. [4.2]
Record Information
- Source Institution:
- Florida International University
- Rights Management:
- Please contact the owning institution for licensing and permissions. It is the user's responsibility to ensure use does not violate any third party rights.
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