open file - Viru Peipsi

LIFE-Environment project
“Viru-Peipsi CAMP”
Climate change impact on the rivers
runoff in Viru-Peipsi catchment area
Arvo Järvet
Tallinn, February 2003

Introduction
Global climate change due to the increase of greenhouse gas concentration in
the atmosphere is a powerful factor expressing the anthropogenic stress on
natural environment. The highest warming is expected to take place in high
latitudes. Water resources are very sensitive to climate change and studies on
this topic have been carried out for many regions in Europe. Possible climate
warming can cause significant changes in hydrological regime and water
resources, including the rivers runoff.
Understanding the sensitivity of water resources is the first and one of most
important steps in the climate change impact assessment. Impact research
needs to address these problems include development of 1) a more physically
based understanding of hydrological processes and their interactions, 2)
hydrological parameter measurement and estimation techniques for
application over a range of spatial and temporal scales, and 3) modular
modelling tools to provide a framework to facilitate water management
research (Leavesley, 1994).
Water balance model WatBal
An assessment of climate change impacts on water resources is a complex
process. Different macro-scale and landscape-scale hydrologic models are used
for this purpose. These models usually require detailed climatic and other input
data on the site or area of interest. Examples of these models include also
hydrological catchment models, by which can be simulate changes in local
hydrologic regime of rivers under climate change scenarios.
Hydrological models provide a framework in which to conceptualize and
investigate the relationships between climate and water resources. Results of
this study could also be necessary information in general water resources
planning; however they are seldom used for it at present. Possible climate
warming can cause significant changes in hydrological regime and water
resources. The key problem is, how will change precipitation amounts and snow
cover regime. Rivers runoff, groundwater level and recharge, land drainage and
water resources management directly depend upon them.
To investigate the influence of climate change on river runoff, the point model
WatBal (Yates, 1994) was applied. This model, realised as a MS Excel macro, is
considered to be a suitable tool for assessments of climate change impact on
river runoff (Yates, Strzepek, 1994). It was validated for Estonia and used within
the implementation of climate change impact research programmes (Järvet et
al, 2000). General calibration and validation of the WatBal model for Estonian
conditions was made. Different decades within the baseline period (1961–1990)
were used for calibration and validation of the model.

Climate change scenarios used in modelling of river runoff
MAGICC model and SCENGEN program were applied for climate
change scenario generation in this study. Three alternative greenhouse gas
emission scenarios developed by IPCC (IS92a, IS92c, IS92e) are combined
with results of two general circulation model (GCM) experiences (HadCM2,
ECHAM3TR). As a result, six climate change scenarios up to the year 2100
are prepared for modelling climate change impact on river runoff. The
following abbreviations are used:
HAD - HadCM2 model,
HAM - ECHAM3TR model,
MID - IPCC medium emission scenario (IS92a),
MIN - IPCC minimum emission scenario (IS92c),
MAX - IPCC maximum emission scenario (IS92e).
GCM results are available for 5x5 degree cells. Therefore, the territory of
Estonia is covered by two cells. The border between West and East Estonia
is, in this case, 25°E. The studied watersheds, presented in Table 1, are
located in eastern sector.
In general, results of the both GCMs are quite similar. They project higher
increase of air temperature during the winter half-year (October–March) and
lower increase in the period April–September. Although, the German model
(ECHAM3TR) developed by Max Planck Institute for Meteorology in Hamburg
expects higher warming than the British (Hadley Centre) one – HadCM2. The
increase of air temperature in East Estonia should be higher than in West
Estonia, especially in winter.
Modelling results
Using the WatBal model, changes in river runoff in case of the six climate
scenarios were calculated for all 14 studied river basins. The modelled
changes in annual mean runoff in different basins and scenarios range from
+5% (River Kunda) to +72% (Emajõgi River in station Tartu). Changes in
annual runoff are presented in Table2. The HadCM2 model shows less
increase of runoff while the ECHAM3TR model indicates more increase. The
emission scenarios have rather linear differences. The lowest increase in river
runoff is projected by the HADMIN scenario, the highest one – by HAMMAX.
The highest increase in annual runoff is calculated for Emajõgi River
(catchment area 7840 km 2 ), and also for small river basin Kääpa in not far
from Lake Peipsi. In general, an increase of annual runoff by 20–30 per cent
(HADMID) or by 40–50 per cent (HAMMID) are modelled for the year 2100.
These changes can be consider as significant.

Table1. Changes in annual runoff according to different climate change
scenarios (percentages)
River Station HADMID HADMIN HADMAX HAMMID HAMMIN HAMMAX
Ahja Ahja 26 13 31 39 21 51
Ahja Koorvere 36 24 40 48 32 59
Avijo Mulgi 24 11 30 41 21 54
Emajõgi Tartu 46 33 51 60 42 72
Kääpa Kääpa 30 16 36 48 27 61
Kunda Sämi 15 5 19 27 13 36
Piiga009 Piigaste 18 7 22 31 15 41
Põltsamaa Pajusi 23 11 28 37 19 46
Pungerja Roostoja 22 10 28 38 20 49
Purtse Lüganuse 18 6 23 33 15 43
Tagajõgi Tudulinna 22 9 28 40 20 52
Võhandu Räpina 26 14 31 40 22 51
Võhandu Himmiste 29 16 33 42 24 54
Not only total increase of annual runoff is important but also its seasonal
distribution. In most of the impact studies, the consequences of a greenhouse
effect for runoff are analysed and discussed, while seasonal patterns of runoff
have received less attention, especially concerning their regularity. Modelling
results demonstrate a possibility of enormous changes in seasonal runoff on
the eastern part of Estonia. The results below (Figures 1–3) illustrate
geographical differences in the sensitivity of runoff to climate change.
Maximum runoff is more sensitive than minimum runoff.
For the studied rivers, the modelled annual curve of runoff is similar to
baseline. A decrease of modelled runoff in spring and its increase in autumn
is typical to all river basins, especially to the rivers of North-Estonia.
Figures 1–3 demonstrate a variety of runoff responses to climate change in
different landscape regions. Observed curves of monthly runoff for the
baseline period (1961–1990) and modelled curves for the year 2100 are
presented. In addition to the medium climate change scenarios HADMID and
HAMMID, HADMIN as the lowest change scenario and HAMMAX as the
highest one are demonstrated.
Võhandu River basin is located in South-East Estonia in the region of the
most continental climate. There, changes in annual course of runoff will be the
less remarkable (Fig. 1). The runoff maximum in spring will move by a month
earlier, but will not decrease. ECHAM3TR model indicates even an increase
of the maximum.

mm/day
1.60
1.40
1.20
1.00
0.80
0.60
0.40
0.20
0.00
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan
Baseline
HADMID
HADMIN
HAMMID
HAMMAX
Fig. 1. Changes in monthly runoff in Võhandu River (station Räpina).
Modelled data for Emajõgi River basin (Fig. 2) have the highest increase in
runoff. But the predicted seasonal variations of discharge are quite similar to
the previous example. The increase in winter runoff and its maximum in
March in case of Emajõgi River basin is higher. It is caused by a fact that this
river has the largest catchment area and runoff is naturally regulated by Lake
Võrtsjärv.
1.60
1.40
mm/day
1.20
1.00
0.80
0.60
0.40
0.20
0.00
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan
Baseline
HADMID
HADMIN
HAMMID
HAMMAX
Fig. 2. Changes in monthly runoff in Emajõgi River basin (station Tartu).
The Kunda River basin is typical to a limestone plateau and a karst region in
North Estonia. It has a great groundwater inflow that makes slower the runoff
decrease after spring maximum, and higher the level of runoff minimum in
summer. Both the maximum in spring and minimum in summer will be shifted
earlier in case of climate change (Fig. 3). The increase of runoff in autumn will
be significant in Kunda River basin.

2.50
mm/day
2.00
1.50
1.00
0.50
Baseline
HADMID
HADMIN
HAMMID
HAMMAX
0.00
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan
Fig. 3. Changes in monthly runoff in Kunda River (station Sämi).
Shift of spring runoff maximum earlier will result in longer duration of summer
low water period and in decrease of total runoff during vegetation period (from
April to September) in many river basins of Estonia. The area of increased
runoff in summer is located in South-East Estonia and of decreased values in
the rest of the territory. The most remarkable decrease is modelled for rivers
with relatively high spring maximum runoff and not higher natural regulation
(River Tagajõgi and River Pedja).
There are big differences in the ratio of minimum and maximum runoff
between the river basins, although the difference between modelled and
observed monthly minimum runoff has a low regional variation and was
positive. It indicates that change in minimum runoff is not projected in case of
climate warming, but the decrease of maximum runoff may be significant. The
ratio between maximum and minimum monthly runoff will decrease very
much. Therefore, seasonal fluctuations of runoff will remarkably diminish due
to climate change and natural regulation of runoff will be increased (Table 2).
Table 2. Changes of coefficient of annual runoff natural regulation
River–station Observe HADMID HADMIN HADMAX
d
Ahja–Ahja 0.87 0.90 0.89 0.90
Ahja–Koorvere 0.88 0.91 0.90 0.91
Avijōgi–Mulgi 0.75 0.79 0.78 0.79
Emajōgi–Tartu 0.90 0.91 0.91 0.91
Kunda–Sämi 0.85 0.89 0.88 0.88
Kääpa–Kääpa 0.78 0.83 0.81 0.82
Pedja–Tõrve 0.78 0.81 0.80 0.81
Piigaste–Piigaste 0.82 0.85 0.83 0.86
Pōltsamaa–Pajusi 0.85 0.88 0.88 0.87
Pungerja–Roostoja 0.75 0.80 0.78 0.80
Purtse–Lüganuse 0.77 0.81 0.79 0.81

Tagajõgi– 0.69 0.74 0.71 0.74
Tudulinna
Vōhandu–Räpina 0.88 0.89 0.89 0.88
Vōhandu–Himmiste 0.87 0.89 0.90 0.87
Impact on the water management
The rivers runoff maximum in spring diminishes, and starts a month earlier (in
March instead of April). However, the autumn and winter runoffs substantially
increase and therefore the difference between maximum and minimum runoff
will be decreased. Low flow characteristics of rivers are important for different
water-based activities and is required for such water resource management
issues as water supply, water quality and quantity estimates. If minimum
runoff will be increased, that it is positive factor for rivers water management,
especially for wastewater discharge and recreational use of rivers (Table 3).
Table 3. Comparison of the climate change impacts on the different
water regime and water resources elements
Water Resources Positive Results
Element
Changes in Rivers Runoff
Increase winter Favourable ecological
minimum runoff condition, diminishing
Decrease maximum
runoff in spring
Longer summer
minimum runoff period
Increase maximum
runoff in autumn
Changes in
Agricultural Runoff
floods in spring
Diminishing floods in
spring
Better ecological
conditions in drainaged
forest areas
Favourable ecological
condition for water bodies,
Smaller peak flow in
spring, diminish of
pollution load and washoff
of fertilizers
Negative Results
Longer summer
minimum runoff period,
diminishing water
capacity in soil
Unfavourable ecological
condition in rivers,
increase high plant and
algal productivity in
lakes and water
reservoirs, increase the
evaporation rate on the
surface of water bodies
More floods in autumn
and inadequate
drainage of agricultural
land
Difficulties in the harvest
period in autumn

Changes in Water
Level and Storage in
Lakes
Water level Decrease the flooded
areas surround of lakes
during the higher water
period
Storage of lakes Increase of total and
active storage of lakes
during winter period
Possible decrease the
level in the end of
summer under the
optimal level
Conclusions
In general, all climate change scenarios for Estonia forecast mild winters, a
decrease in snow cover and an increase in the duration of dry periods in mid–
summer. The predicted global warming will cause more changes in the water
balance elements in the cold period than in the warm season. Modelled
annual runoff and its seasonal variability in study area are not very sensitive
to climate change. The main results of the study are following:
• Periodical fluctuations of water level and river runoff. Long time
series of annual precipitation has a significant periodicity of 25–35
years in Estonia during more than a century. It causes long-term
fluctuations in hydrological regime and alternation of wet and dry
periods also in the future.
• Increase in annual runoff. Due to the climate change, annual runoff
will increase by 20–40 % in the average, for the year 2100, but
modelled river runoff show a great spatial variation.
• Significant increase in winter runoff. During mild winters, duration of
snow and ice cover should decrease, winter weather should be
changed more unstable, freezing and melting periods should
alternate.
• Decrease of spring runoff maximum and its shift earlier. Mild winters
cause faster melting of snow and earlier beginning of spring
hydrological season. Frequent melting periods in winter prevent big
accumulation of snow. The mean maximum runoff should move
from April to March.
• Increase of river runoff in autumn. This is directly caused by
significant increase of autumn precipitation predicted by both of the
GCMs. In East-Estonia autumn maximum runoff would not exceed
maximum runoff in spring.
• Lengthening of the period of minimum runoff in summer. Due to
faster melting of snow, decreasing and moving earlier of runoff
maximum in spring, dry period should begin earlier. Minimum runoff
period when rivers receive the majority of water from groundwater,

will start not in June but in May. It could cause a severe water
deficit in some small river basins in catchment area of River Pedja.
• Maximum runoff to be more sensitive than minimum runoff. Spring
floods have decreased, because of the lack of snow in the end of
winter period.
• All these modelled changes can be considered to be inside the
observed natural variation of rivers runoff during the baseline period
in 1961–1990.
• Changes of hydrological conditions should be translated into
changes in ecology of water-bodies also, because a number of
ecological processes dependent from hydrological conditions. It can
be concluded that positive impacts of climate warming on ecological
state of water-bodies are prevailing in study area.
• If minimum runoff will increase then it will act as a positive factor for
water management of rivers, especially for wastewater discharge,
navigation and recreational use.
References
Järvet, A., Jaagus, J., Roosaare, J., Tamm, T. and Vallner, L. 2000. Impact of
Climate Change on Water Balance Elements in Estonia. – Estonia,
Geographical Studies 8 (Eds. Tiia Kaare and Jaan-Mati Punning). Estonian
Academy Publishers, Tallinn, pp. 35–55.
Leavesley, G.H. 1994. Modeling the effects of climate change on water
resources - a review. - Climate Change 28: 159-177.
Yates, D., 1997. Approaches to continental scale runoff for integrated
assessment models. J. Hydrol., 201, 289–310.
Yates, D. & Strzepek, K., 1994. Comparison of models for climate change
assessment of river basin runoff. IIASA WP-94-45.