Variable: Lake Levels and area
The volume of water in surface-storage units (lakes reservoirs and wetlands) reflects both
atmospheric and hydrological conditions. If climate changes, then lakes and wetlands will
reflect this promptly.
1.Definition and units
A lake or reservoir may be a homogeneous body of water, in which case a single monitoring
site may be sufficient. On the other hand it may consist of waters of different characteristics.
For example it may have a deep area and one or more shallow areas with different
characteristics. In this case each should be monitored.
Water level, or stage1, is the elevation of the water surface of a stream, lake, or other water
body relative to a datum.
Lake area is the surface area of a lake, it can be determined from satellite measurements.
(Submit weekly) Surface and sub-surface water temperature,
date of freeze-up and date of break-up (of 150 priority lakes in GTN-L)
Unit of measure
Maximum depth of Lake/Reservoir in meters to one decimal place
Area of lake in km2 to one decimal place
Volume of lake/reservoir in km3 to one decimal place2
2. Existing measurements methods and standards
WMO and ISO Standards
Information relating to hydrological observing stations and to lake measurements are
described in the Volume III (Hydrology) of Technical Regulations (WMO-No.49) in section
[D.1.1.]5 and in the WMO Guide to hydrological practices (WMO-No.168). The sections on
lake level specify the requirements in the establishment and operation of a hydrometric station
for the measurement of stage. Gauges on lakes and reservoirs are normally located near their
outlets, but sufficiently upstream to avoid the influence of drawdown. It should be observed
with a precision of one centimetre in general and to three millimetres at continuous-record
gauging stations. (WMO-49, WMO-168).
The ISO standards related to measures of lake are Liquid Flow Measurement in Open
Channels: Vocabulary and Symbols in its Third edition and the 1981 Liquid Flow
Measurement in Open Channels. Part 1: Establishment and operation of a gauging station and
Part 2: Determination of stage-discharge relation.
2.1 In situ measurement
Measuring lake level
Non-recording gauges
Several types of non-recording gauges for measuring stage are used in hydrometric practice.
The common gauges are of the following types:
1
The vertical distance of the water surface of a stream, lake, or reservoir relative to a gauge datum
UNEP- Global Environment Monitoring System (GEMS) Water Programme
http://www.gemswater.org/common/pdfs/op_guide_station_form.xls
2
1
(a) Graduated vertical staff gauge;
(b) Ramp or inclined gauge;
(c) Wire-weight gauge installed on a structure above the stream; and
(d) Graduated rod, tape, wire or point gauge for measuring the distance to the water surface.
Recording gauges
Many different types of continuously recording stage gauges are in use. They may be
classified according to both mode of actuation and mode of recording.
A commonly used installation consists of a stilling well connected to the stream by pipes and
a float in the stilling well connected to a wheel on a recorder by a beaded wire or perforated
tape. In high velocity streams, it may be necessary to install static tubes on the end of the
intake pipes to avoid drawdown of the water level in the well.
Procedures for measurement of stage
Establishment of gauge datum
To avoid negative readings, the gauge should be set so that a reading of zero is below the
lowest anticipated stage. The gauge datum should be checked annually by levels from local
benchmarks. It is important to maintain the same gauge datum throughout the period of record.
If feasible, the local gauge datum should be tied to a national or regional datum.
Recording gauges
The graphical (analogue), digital, electronic, or telemetering device recorder is set by
reference to an auxiliary tape-float gauge or to a staff gauge located inside the stilling well. In
addition, a staff, ramp or wire-weight gauge set to the same datum, is necessary to compare
the water surface elevation in the stilling well with that of the river. For gauges with gaspurge systems and no stilling well, the staff, ramp, or wire weight gauge in the river should
serve as the reference gauge. Small differences usually will occur because of velocity past the
ends of the intake pipes. Large differences indicate that the intake pipes may be obstructed.
Frequency of measurement
The frequency of recording of water level is determined by the hydrological regime of the
water body and by the purposes for collecting the data. A daily measurement of stage is
usually sufficient in lakes and reservoirs for the purpose of computing changes in storage.
2.2
Satellite Measurement
Remote sensing (satellite altimetry and monitoring of the area of lakes and reservoirs) has the
potential to provide some of lakes and reservoirs attributes (lake names, location, country,
surface area and elevation estimated from Operational Navigational Charts maps, etc.;
http://wwwcpg.mssl.ucl.ac.uk/orgs/un/glaccd/html/mgld.html).3
Area and level measurement
In the past, hydrological information could often be difficult to obtain by ground-based gauge
instruments due to the inaccessibility of the region, the sparse distribution of gauge stations or
the slow dissemination of data due to national policy.
Radar altimetry can avoid these obstacles because it is located on satellites 800 to 1300
kilometres above the Earth and is able to measure large lakes’ surface water height to two
centimetres accuracy and rivers to ten centimetres by sending 1800 separate radar pulses over
3
http://www.fao.org/DOCREP/005/AC666E/ac666e08.htm
2
bodies of water per second and recording how long their echoes take to bounce back. In
addition, these data are available in near-real time. CryoSat-2, the next ESA radar altimetry
mission, expected to launch in 2009, is designed to measure changing ice fields, but it will
also contribute to monitoring water resources by acquiring samples of data from its new
generation radar altimeter over inland water bodies upon request from scientists for
experimental purposes.
A follow on to CryoSat, ESA Earth Explorer ice mission, which was lost at launch in 2005
due to an anomaly in the Russian launcher, CryoSat-2 will fly an enhanced radar altimeter
instrument, called the Synthetic Aperture Interferometric Radar Altimeter (SIRAL) which
will allow it to improve the resolution of the measurements by increasing the number of
separate radar pulses it sends down to Earth every second from 1800 to up to 17 800. The
experiment will demonstrate how to benefit from novel technologies to serve emerging
science fields, such as hydrology, from space.4
Over the past decade, ERS-1, ERS-2 and, more recently the ENVISAT mission, have
provided altimeters which are engineered to collect data from varying topographic surfaces in
addition to their primary mission of open ocean measurements. This has now allowed the
extraction of long time series of data over inland water5.
Recent research into the application of altimetry for monitoring river and lakes levels has
been carried out and demonstrated the advantages of using data derived from satellite as
global coverage and regular temporal sampling of the data sets. Together with the European
Space Agency (ESA), De Montfort University (UK) developed a system to obtain an
estimation of River and Lake heights from both ERS and Envisat data. De Montfort
University (DMU) developed an automated system to produce two types of products called
River Lake Hydrology product (RLH) and River Lake Altimetry product (RLA).6
ENVISAT-ERS Exploitation River and Lake Product Handbook describes the hydrology
products derived from ERS-1/2 and Envisat satellite altimeter data. The document contains
five sections. In Section 2, the background of satellite altimetry is briefly described. Section 3
discusses the processing applied to these data to extract meaningful heights over inland water.
In Section 4, the detailed product specification and formatting are defined. Section 5 contains
information on the xml front end available for the general user hydrology product.
Generation of lake bathymetry using geo-referenced sonar sounding and satellite
imagery.
Bathymetric information on lakes and reservoirs has important value in hydrology. Besides
water level – volume - lake area or stage curve relationships, multi temporal comparison
between bathymetries.
Methodology
Generation of a bathymetric surface or map basically consists of 3 parts: geo referenced depth
data acquisition, generation of a bathymetric surface using interpolation methods and
verification of mapping accuracy.
Data acquisition
4
http://www.earsc.org/web/template.php?page=individual&ID=208
ECV-T4-lake-ref-32-river-lake-from radar altimetry.pdf
6
http://earth.esa.int/riverandlake/, ECV-T4-lake-ref-41-ENVISAT-ERS Exploitation River and Lake Product-Handbook_2_0.pdf
5
3
Water depths are registered using a portable sounder connected to a Global Positioning
System (GPS) installed on a small boat. The sounder uses a single frequency transductor of
200 kHz to measure the distance from sensor to lake bottom with an accuracy of 10 cm. The
GPS records both the location coordinates and the depth measurement of the sounder.
Depending on the type of GPS used (DGPS, WAAS-enabled GPS, and handheld GPS); the
location can be measured with an accuracy varying from 15 meters to a few centimetres.7
Inland and Nearshore Coastal Water Quality Remote Sensing
The Group on Earth Observations (GEO) has planned an Inland and Nearshore Coastal Water
Quality Remote Sensing Workshop (27-29 March 2007, Geneva), which covered the
following topics: inland waters and coastal land influenced waters data reception,
preprocessing, distribution remote sensors (spatial, temporal, spectral resolutions) processing
algorithm issues atmospheric correction air-water interface corrections optical water quality
variables derived variables (i.e. eutrophication index) calibration/validation issues. At the
same time, the University of Wisconsin (UW) has been active in pursuing the objectives of
the IGWCO, including the launch of two initiatives:
•the Freshwater Color Coordination Group
•the Multisensor Space-borne Monitoring of Global Large Lakes: Towards an Operational
Assessment of Trends in Water Quantity and Quality. The goals of this initiative are to:
 produce satellite-derived map showing water level fluctuations over 40 large lakes
worldwide
 evaluate the ability of Ice, Cloud, and land Elevation Satellite (ICES) / Geoscience
Laser Altimeter System (GLAS) to provide accurate lake level measurements, for the
same 40 lakes8
 use field observations from Global Environment Monitoring Program (GEMS)
database and corrected satellite imagery to classify second set of lakes
 derive basic operational algorithms
 quantify remote sensing costs and data processing issues
3. Contributing Networks
Proposed GCOS Baseline Lake Level/Area Network based on TOPC priority list.
3.1 Available data
International Centre of Data on Hydrology of Lakes and Reservoirs
A draft proposal on the establishment of an International Centre of Data on Hydrology of
Lakes and Reservoirs (HYDROLARE) has been developed by the State Hydrological
Institute (SHI) of St. Petersburg. SHI manages the hydrological network on lakes and
reservoirs of the Russian Federation, which began in 1860, peaked in the 1980s at 493
stations, declined in the 1990s, and has stabilized now at 377 stations. Data and information
7
ECV-T4-lake-ref-33-Generation of lake bathymetry using geo-referefnced sonar sounding and satellite imagery.pdf
The NASA-sponsored Surface Water Working Group has established a framework for advancing satellite observations of river discharge
and water storage changes which focuses on obtaining measurements of water surface height (stage), slope, and extent. Satellite laser
altimetry provides a method to obtain these inland water parameters and contribute to global water balance monitoring.
8
4
on this network is archived electronically in hydrological yearbooks and includes lake levels,
surface water temperatures, water temperature profiles, heat content, ice cover and thickness,
snow depth, wind, water balance, waves and currents. HYDROLARE is being proposed to
meet the need for global data on lakes and reservoirs. The amount of water stored in the
world’s145 largest lakes is estimated as 168 000 km3. The overall objective of the proposed
centre is to establish, develop and regularly update an international database on hydrological
regime of lakes and reservoirs in order to:
• stimulate the development of a global monitoring system on lakes and reservoirs for rational
use, preservation and management of global water resources;
• improve the knowledge of lateral fluxes transformation within lakes and reservoirs; and
• supply data for scientific and educational purposes, modelling, and the development of
global and regional projects and programs.
The first stage of developing HYDROLARE would consist of collecting, processing and
distributing metadata and annually updated hydrometeorological observations for lakes and
reservoirs including water levels, changes in water storage, inflow/outflow data, and ice
conditions.
At the moment the SHI is currently not in a position to serve as a World Data Centre, the
GTN-H could assist in the development of a global data centre for lake data. The suggestion
was made to write a letter in support of the Russian Federation proposal. Another suggestion
was made to consider other organizations that could host such a data centre, such as
GEMS/Water. The role of the International Lake Environment Committee (ILEC) should also
be considered. Both in situ and satellite-derived data sets should be considered.
Sandy Harrison then reported on work undertaken by the GCOS/GTOS Terrestrial
Observation Panel for Climate (TOPC) on identifying an initial priority list of 156 lakes for
which data on area, level and, if possible, freeze and break-up dates should be collected.
The TOPC approach to monitoring is to focus primarily on closed-basin lakes but including
major ephemeral lakes and a selection of the largest open lakes. The major consideration in
the choice of sites is to ensure a representative sample of each type of lake (where present) in
each region. Where multiple possibilities for monitoring exist, preference should be given to
large lakes to facilitate the use of satellite observations. Secondary considerations in the
choice of sites are:
(a)water use, (b) relevance for other monitoring purposes (e.g. water quality, biodiversity,
pollution), and (c) the existence of a longer-term, historic or palaeoclimatic record at the site.
The initial target of 156 lakes worldwide, ranging in size from 15 to 374 000 km2, will be of
immediate benefit to climate modellers, though the inventory will have to gradually increase
to on the order of 500 lakes to ensure fully adequate regional coverage and sufficient sites to
ensure replicability of the derived records. Lake level and area need to be measured ideally
weekly or at least monthly, with a horizontal resolution of 10 m and a vertical resolution of at
least 5 cm. These measurements would be made by national hydrological services and should
be provided to a designated international data centre.
The meeting recommended that the proposal by the Russian Federation be supported provided
that the TOPC approach and recommendations are incorporated.
It was noted that there may be existing global datasets and providers elsewhere (e.g., the
University of New Hampshire holds data for another 200 lakes) and that an inventory of such
should also be considered in the development of a global data centre.
For the purposes of efficiency in addressing hydrological variables of relevance to the GTN-H,
the meeting participants agreed to merge the surface storage flux variable with the lake
levels/area variable in the GTN-H table of variables.
5
International Lake Environment Committee
At the present, coherent lake reservoir data bases with global coverage do not exist, however
pieces are available at various locations. The International Lake Environment Committee 9
maintains a database of lakes and reservoirs10; however this database does not contain timeseries of relevant hydrological variables. Another lake database, the MSSL/WCMC/UN
Global Lake and Catchment Conservation Database 11 , was developed by Mullard Space
Science Laboratory of the University College London as a prototype for remote sensing
applications (Birkett and Mason, 1995). It includes over 1400 lakes and reservoirs, but a very
limited set of attributes (lake names, location, country, surface area and elevation estimated
from Operational Navigational Charts maps, etc. ;
IGWCO Water Cycle Variable12
Streamflow and surface water storage (runoff)
Main objective: The establishment of an integrated stream/lake/reservoir database, comprised
of in-situ and remotely-sensed capacity/flow monitoring in real time.
Given that water resource managers need timely and accurate information with respect to
river flow and water storage in lakes and reservoirs to prevent, among other things, waterrelated disasters, the IGWCO has emphasized the development of a Global Runoff
Monitoring Project. The objective of this initiative is to provide temporal observations and
analyses of surface runoff and lake/reservoir storage variations and variability, by means of
integrated in-situ and remotely sensed real-time monitoring. In the year since it was first
proposed, the project has expanded to include participants such as the ESA, GEO and GTN-H.
Participants: GEO, GTN-H/GTN-R, ESA, De Monfort University, WHYCOS, WMO
The Global Runoff Monitoring Project first proposed at CEOP/IGWCO Workshop (March
2006). Project subsequently renamed Hydrological Applications and Runoff Network
(HARON) with participation of GEO and GTN-H.
Participation of ESA encouraged, following success of “River-Lake” project with ENVISAT
altimetry products, in conjunction with Water Elevation Recovery Missions (WatER)
Initiative.
International Commission on Large Dams
The International Commission on Large Dams (ICOLD) maintains a registry of dams
(ICOLD, 1988). This database was originally published in books (paper form only), but
recently became available electronically on CD-ROM. The ICOLD registry contains
information on several thousand reservoirs, assembled from an engineering perspective. One
criterion for including reservoirs in this registry was to have 15 m or higher construction, thus
potentially leaving out many reservoirs in plain regions where several metres high dam
construction might result in large inundation. While detailed information on the dam
construction (purpose, height, length and volume of the construction, construction type,
spillway capacity,) are provided beside basic information on the reservoir itself (maximum
capacity, reservoir surface area, etc.), but other essential information (including location,
mean discharge through the reservoir) is missing. The only way to geographically identify
these reservoirs is by the nearest city and river names that are provided as part of the database.
Several attempts have been made to identify these dams on maps and correct the information
9
ILEC, a non-governmental organisation established in 1986 in Japan, http://www.ilec.or.ip/e_ index.html
http://www.ilec.or.jp/database/index/idx-lakes.html
11
http://wwwcpg.mssl.ucl.ac.uk/orgs/un/glaccd/html/mgld.html
12
http://www.wmo.int/web/homs/igwco/reports/IGWCO_assessment_report.pdf
10
6
(by UNH, GRDC, CESR). - In related efforts, USGS developed a dam inventory for the US,
and Russia maintains a database of lakes and reservoirs of the national territory.
The merging of the above mentioned lake and reservoir data sets with the available digital
maps could be a basis for a more detailed global lake/reservoir database, but this work is not
trivial and needs extensive manual effort.
It was noted that at present no dynamic information is available on lakes and reservoirs (level
changes, operation, etc.). Remote sensing (satellite altimetry, monitoring of the surface area)
has the potential to solve this problem. The group was informed that NASA GSFC is working
on using satellite altimetry (TOPEX/POSEIDON, ERS-1) to measure lake and reservoir levels
(Birkett, 1998).
At the present time, global information on surface water storage in lakes, reservoirs and
wetlands is inadequate in terms of coverage and time-series observation of changes in the
storage volume at all scales. However, it was noted that higher resolution information
available only in some regions is also important, given the regional nature of some
hydrological issues.
International Great Lakes Datum
International Great Lakes Datum (IGLD) is the reference system by which Great Lakes-St.
Lawrence River Basin water levels are measured. It consists of benchmarks at various
locations on the lakes and St. Lawrence River that roughly coincides with sea level. All water
levels are measured in feet or meters above this point. Movements in the earth's crust
necessitate updating this datum every 25-30 years. The first IGLD was based upon
measurements and bench marks that centered on the year 1955, and it was called IGLD
(1955). The most recently updated datum uses calculations that center on 1985, and it is
called IGLD (1985). Measurements recorded in NGVD (1929) or IGLD (1955) need to be
converted to IGLD (1985) measurements before they can be used in comparison situations.13
Canadian Hydrographic Service14
Lakes and wetland areas are strongly driven by climatic conditions and also play a critical
role in the cycling of carbon. Canada has 24% of the world's wetlands and these clearly need
to be monitored. The country is also blessed with immense aquatic resources in its lakes (e.g.
the Great Lakes, shared with the United States, contain about 18 per cent of the world supply
of fresh water). The Canadian Hydrographic Service, part of DFO, collects data for the Great
Lakes and other large Canadian lakes and possesses records going back to 1918 while a
number of smaller lakes have also been monitored for many years, for water management or
research purposes. The Ecological Monitoring and Assessment Network (EMAN), discussed
later in this report, is a link to many such research and monitoring sites in Canada15
Key actions
The State Hydrological Institute (SHI), St. Petersburg, Russia expressed an interest in hosting
a global data centre for lakes and reservoirs. WMO intends to follow up on these activities.
Furthermore, contacts should be made with ILEC to determine a possible inclusion of its
database.
13
ECV-T4-lake-ref-37-International Great Lakes Datum 1985.pdf
http://www.ec.gc.ca/climate/CCAF-FACC/Science/nat2002/f49#f49
15
The Experimental Lakes Area (ELA) in western Ontario, the Turkey Lakes in southern Ontario, and Lake Kejimkujik in Nova Scotia are
examples of such research initiatives that are useful in the assessment of ecosystem and aquatic impacts of climate change.
14
7
Lake and River Freeze-Up (FU) and Break-Up (BU)
Several studies have shown that long series of lake ice observations can serve as a proxy
climate records, and the monitoring of freeze-up and break-up trends may provide a
convenient integrated and seasonally specific index of climatic perturbations. Some authors
(e.g. Livingstone, 1997) are of the opinion that historical lake ice records may be a more
reliable indicator of past local and regional climatic changes than even air temperature records
themselves, since the latter are frequently subject to inhomogeneities and bias resulting in
station alterations and observer changes. In particular, inter-annual variations in lake ice cover
duration and thickness may allow estimates of local climatic variability and long-term
changes in lake ice phenology may provide a robust indication of climatic change.
Ice cover on a lake also impacts greatly on the chemical characteristics of the underlying
water, for ice cuts the lake water off from direct atmospheric influences and it reduces
significantly the amount of shortwave radiation (sunlight) that penetrates to the water below.
The amount of this reduction depends upon ice type and the properties of any overlying snow.
For example, bubble-free black ice is essentially transparent to sunlight, but white ice and
snow reflect much of the incoming radiation, and limit its penetration. Radiation that does
penetrate the ice can cause a rise in water temperature. Ice cover restricts the movement of
gases between water and air. This commonly results in a depletion of dissolved oxygen in the
lake, but a buildup of carbon dioxide, methane, hydrogen sulphide, and other reduced gases.
Sometimes, however, the freezeout of oxygen during ice formation can compensate for
oxygen loss from other processes. An increase in other constituents (e.g. potassium, sodium,
calcium) also occurs as ice forms, but is reversed as ice melts. Such changes in energy and
chemistry have implications for the biota and whole productivity of a lake. Other
consequences associated with ice formation can include a loss in volume of water, decline in
the amount of unfrozen lake bottom, a decrease in turbidity, and reduction in the amount of
water moving through the lake when ice formation reduces (or even stops) the amount of
water entering or leaving the lake.
2. Existing measurements methods and standards
2.1 In situ measurement
Canadian Freshwater Ice - In Situ Monitoring Activities
A database of Canadian lake ice conditions is maintained by the Atmospheric Environment
Service of Environment Canada. The database for lake, river and coastal sea ice sites contains
information on the timing of freeze-up and break-up, maximum seasonal ice thickness, and
the state of the ice surface with respect to the traffic it can support. The four standard
observed ice condition dates are first permanent ice (FPI), complete freeze over (CFO), first
deterioration of ice (FDI), and water clear of ice (WCI) (Skinner, 1992). CFO and WCI are
the two main series used as these have been found to contain the least noise. There are 250
lakes in the database, with observations extending as far back as the 1940s. In 1992 W.
Skinner (AES Climate Research Branch) determined there were 29 lakes with sufficiently
long and complete records for climate monitoring purposes.
While numerous studies have used the Canadian freeze-up/break-up data to demonstrate
relationships to temperature and other climatic variables (e.g. Da Silva, 1985; Anderson, 1987;
Skinner, 1992), in situ data alone are not considered suitable for a Canadian lake ice
monitoring program. The in situ data are subjective and it is difficult to determine their
8
accuracy and homogeneity. Because of this, Skinner (1992, p. 44) concluded that surfacebased observations of lake ice conditions can only be used as the initial ground truth "for the
more spatially and temporally consistent satellite monitoring of lake freeze-up and break-up
and lake surface temperatures". However, in situ data are important for validation of lake ice
models, and satellite algorithms, particularly those sites with long term data which overlap the
satellite record and which are being used to validate satellite methods e.g. the Back Bay site
on Great Slave Lake.
2.2
Satellite Measurement
LAKE ICE AND SSM/I
A major component of current CRYSYS lake ice research is determining the potential
usefulness of passive microwave satellite data for extracting information related to lake ice
processes. CRYSYS data analysis has focussed on Great Slave Lake in northern Canada and
results have confirmed that it is possible to discriminate between areas of ice cover and open
water using SSM/I (Special Sensor Microwave Imagery) 85 GHz data, hence indicating a
potential to monitor the progression of ice formation and decay over the lake until complete
freeze-over or ice-free conditions exist.
Figure 1: SSM/I 85 GHz horizontal polarization brightness temperature data mapped over
Great Slave Lake from an orbit pass on June 10, 1992 (source: Anne Walker, MSC, Climate
Research Branch).
Figure 1 above depicts SSM/I 85 GHz horizontal polarization brightness temperature data
mapped over Great Slave Lake from an orbit pass on June 10, 1992. An area of contrasting
low brightness temperatures in the lower right portion of the lake indicates the presence of
open water. This was confirmed from a NOAA AVHRR visible image obtained on the same
day, and from aircraft visual observations. The variability observed during the period
preceding freeze-up is related to weather conditions over the lake (e.g. cloud, rain) and
roughness of the water surface. During the winter season, the brightness temperature trends
are influenced by the accumulation of a snow cover over the ice surface. The variability
9
observed during the spring season before ice break-up occurs may be related to changes
occurring on the ice surface (e.g. snow melt, flooding) or meteorological conditions (e.g. rain).
Several distinct periods of lake ice freeze-up / break-up can be identified:
1.
2.
3.
4.
5.
open water preceding freeze-up
time of freeze-over
winter
onset of spring melt
period preceding ice break-up
The variability observed during the period preceding freeze-up is related to weather
conditions over the lake (e.g. cloud, rain) and roughness of the water surface. During the
winter season, the brightness temperature trends are influenced by the accumulation of a
snow cover over the ice surface. The variability observed during the spring season before ice
break-up occurs may be related to changes occurring on the ice surface (e.g. snow melt,
flooding) or meteorological conditions (e.g. rain)16.
Dates of freeze-up and break-up of ice cover on lakes and rivers are a useful indicator of
climate change17, being well correlated with air temperature during the transition seasons, and
are an important ecological indicator.
Identified GCOS requirements are for daily observations of ice conditions in spring and fall
for selected large lakes and several hundred medium-sized lakes distributed across middle and
high latitudes. There are also associated needs for the selection of a set of GCOS reference
lakes for assessing long-term variability, development of methods for merging in-situ and
remotely sensed information on this parameter, and for a central or several regional archive(s)
of FU/BU information.
The Canadian National Report on Systematic Observations for Climate
Canada has contributed significantly to GCOS in this area since in situ FU/BU observations
exist at several hundred Canadian lake and river sites for various periods, with some sites
going back to the early 1800s18 Though the in situ network has declined significantly over the
past 10 years, efforts are underway to reverse this trend e.g. the EMAN volunteer "Icewatch"
program (see page 54 for EMAN web site address). Satellite-based methods have
demonstrated excellent potential and FU/BU monitoring for large Arctic lakes has already
been implemented using passive microwave observations. This record is being extended back
in time using the available satellite record (1978-present). The Canadian Ice Service (CIS)
began weekly monitoring of ice extent on small lakes in 1995 using NOAA AVHRR and
RADARSAT imagery in support of Canadian Meteorological Centre (CMC) needs for lake
ice coverage in numerical weather models. The program started with 34 lakes and was
increased to 118 lakes by the end of 1998. Canadian researchers are currently working on an
ESA-supported project to develop an operational method for mapping freeze-up and break-up
16
http://www.msc.ec.gc.ca/crysys/education/lakeice/lakeice_edu_e.cfm
Data on river ice are less useful as climate indicators than are data on lake ice (Walsh, 1995) because inflow (and human) effects are
generally more significant in rivers.
18
Canadian FU/BU data up to 1994 have been supplied to the WDC-A and were used in the recent synthesis of Northern Hemisphere trends
in FU/BU dates by Magnuson et al. (2000; Science, 289, 1743-1746)
17
10
dates over large areas of Canada using SAR (ASAR Global Monitoring Mode) and optical
(AATSR) data from the ENVISAT satellite.
The Canadian Ice Service (CIS) monitors Canadian lakes via remote sensing on a regular
basis. Ice coverage is measured in tenths, and from this the freeze-up and break-up dates can
be determined within a ± one week accuracy.
Special Features
 Animation of Lake Melt from May-July 2001
Monitoring Lake Ice
Monitoring lake ice freeze-up and break-up provides a useful seasonally-integrated index of
climatic change. Manual observations of lake freeze-up and break-up ("phenology") have
been made at an extensive network of Canadian sites since the 1800s. Some of these data
were used in a recent paper by Magnuson et al. to document consistent evidence of trends
toward earlier break-up and later freeze-up over many regions of the Northern Hemisphere.
The Canadian network has decreased substantially in recent years, and increasing use is being
made of satellite data, particularly NOAA AVHRR and Radarsat, to monitor lake ice cover.
Investigations to use passive microwave are being undertaken. The advantage of satellite data
is that it provides a complete image of lake ice cover, unlike manual observations which are
limited to the local-scale. Satellite data also allows lake ice monitoring to be carried out over
vast uninhabited areas of Canada, thus providing useful climate information in areas without
surface-based observations. The increasing resolution of climate and weather forecast models
has also created a need for regular monitoring of lake ice coverage from satellite data - the
amount of open water has a major impact on regional-scale processes such as lake-effect
snowfall.
International Polar Year 2007-2008 Activities
Proposal
A network of lake ice study sites will be created in the circumpolar north. The study sites will
be run primarily by schoolteachers and their students with the assistance of scientists and their
students. Freeze-up, break-up and thus ice duration will be recorded. Between freeze-up and
break-up, measurements will include ice thickness, and the depth, density and temperature of
the snow on the ice. The conductive heat flow through the snow will be derived from the
snow measurements. The conductive heat flow determines the ice growth rate and thus the ice
thickness. ArLISON data will be used for running, assessing and improving a numerical
model of contemporary lake ice growth and decay. Data and results will be shared among the
participants via a project Web site. Web-based and tele/video-conference seminars will enable
discussion of ArLISON results, which will be placed in the broader context of polar
environmental science and IPY. A workshop, to be held in summer 2009, will be an
opportunity for all ArLISON participants to meet and discuss their experiences, and the
scientific and educational outcomes of ArLISON.19
Reference:
World Meteorological Organization, 1980: Manual on Stream Gauging.
Volumes I and II, Operational Hydrology Report No. 13. WMO-No. 519, Geneva.
19
http://classic.ipy.org/development/eoi/details.php?id=6
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International Organization for Standardization, 1988: Liquid FlowMeasurement in Open
Channels: Vocabulary and Symbols. Third edition, ISO 772, Geneva.
International Organization for Standardization, 1981: Liquid FlowMeasurement in Open
Channels. Part 1: Establishment and operation of a gauging station and Part 2: Determination
of stage-discharge relation. ISO 1100, Geneva.
Carlson, R.E. and J. Simpson. 1996. Volunteer Lake Monitoring in the Upper Mid-west:
Programs, Techniques, and Technical Recommendations. North American Lake Management
Society, Madison, WI.
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