3.1 Surface-water trends
Individually, these types of surface water provide very different environmental, social and
Changes in the extent of surface water are
economic benefits, but together – and when
measured at five-year intervals relative to a
adequately protected and well managed – they
20-year baseline period (2000–2019) and based
secure vital services for people and help
on the annual aggregation of monthly water
maintain the health and integrity of ecosystems.
occurrence maps. Permanent, seasonal and
It is therefore crucial to examine these water
reservoir data have been merged into a single
bodies together to gain an overall understanding
surface-water trends map (though they are also
of the situation, while also respecting their
presented separately) to depict river basins with
individual importance, exposure to different
the highest changes in surface-water area in the
pressures and threats, and specific management
last five years (2015–2019).
needs. In the following sections, this report presents the mapping and analysis of changes in
Analysis of surface-water extent over the last
permanent water, seasonal water and reservoirs.
20 years reveals that one fifth of the world’s river basins experienced either a high increase or decrease in surface water in the past five years (Figure 5). River basins with increased surfacewater area tended to correspond to locations with a growth in reservoirs, newly inundated land
Online story maps can be accessed on the dedicated case studies website.
(i.e. land intentionally flooded for agriculture) and areas with increased flooding, with
National data of combined surface-water
decreased surface-water areas linked to
changes (i.e. permanent + seasonal + reservoir
locations that experienced drought, increased
changes) per country are available for download
demand and excessive water usage. The
from the indicator 6.6.1 report website.8 The
surface-water changes presented in Figure 5 are
table provides country information on changes in
also indicative of climate change, the impacts of
surface-water area observed in 2015 and 2020,
which have contributed to the drying out of lakes
which are compared against a 20-year reference
in arid regions and expansion of lakes due to
period. Countries can use this tabulated data to
glacial melt and permafrost thawing.
observe the extent to which surface waters are increasing or decreasing.
The map shown in Figure 5 presents the overall changes to all open inland surface waters, including natural waters (rivers and lakes) and artificial reservoirs, both permanent and seasonal.
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See https://stories.sdg661.app/#/pdfs/report-annexes.
PROGRESS ON FRESHWATER ECOSYSTEMS - 2021
