Climate Change Projections

Regional climate change scenarios were constructed based on the outputs of the Had3 and ECHAM4 Global Circulation Models (GCMs). For both model outputs, two scenario variants were used: A2 and B2. The time slices considered were 2010-2039 and 2070-2099. Since the original resolution of the GCMs is quite coarse, a downscaling procedure was used to prepare the CC scenarios for regional modelling with a final resolution of 1 X 1 km2 (see Chapter 2).

The analysis of the scenarios (Fig. 5.3) shows a good deal of similarity between outputs from Had3 and ECHAM4 in terms of monthly changes. The Had3-A2 scenario shows the highest temperature increase (5.1oC). The Had3-B2 shows a future with a moderate temperature increase (3.7oC). According to both scenarios, the

Table 5.2. Summary of the mean annual changes of the main climate parameters. dTMP is annual temperature deviation (°C) from the baseline (1961-1990) value; xPRE is annual precipitation increase related to the baseline value (1961-1990).

Time slice

Model

dTMP

xPRE

2010-2039

ECHAM

2.1

1.13

A2

1.5

1.08

B2

1.6

1.07

2070-2099

ECHAM

5.4

1.10

A2

5.1

1.07

B2

3.7

1.16

summer period is expected to grow more arid, despite an overall increase of annual precipitation in the range of 1.07 to 1.17 times its present value on average. Table 5.2 shows a summary of the projected precipitation and temperature changes.

In the IPCC projections, some key points relevant to Central Asia, and Syr Darya in particular, are:

• for the years 2070-2099, the absolute increase of annual mean temperature will be 4-7°C, while annual precipitation will increase 7-16% as compared to the baseline (1961-1990) interval;

• the temperature variability is expected to increase remarkably: the standard deviation of temperature fluctuations might increase nearly twofold; and

• precipitation variability is expected to significantly increase only under scenario B2 over the period 2070-2099, which also suggests a significant increase of the extremes.

The historic data validate the climate scenarios used in our study: both A2 and B2 scenarios suppose the same tendency for the Central Asian region: overall increase of precipitation as a consequence of global warming. Meteorological observation data in the region (Savoskul et al., 2000) suggest also that variability of climate parameters correlates with climate humidity: the more arid the climate, the less variation in extremes is simulated in the scenarios. For the Syr Darya Basin, it means less climate variability (CV) in the upper reaches of the basin, which is an important note taking into consideration that this is where runoff is formed.

Under the CC scenarios used in this study, the following changes are expected for climate variability. Absolute changes in temperature over the period of 2010-2039 are compared to the ranges of its baseline period variability. For the time slice 2070-2099, the absolute changes of annual means will be far beyond the range of baseline period extremes. At the same time, the temperature variability is expected to increase, e.g. the standard deviation of temperature fluctuations might increase nearly twofold. On the contrary, the absolute increase of precipitation is expected to remain within the range of its current variability. Precipitation variability is not expected to significantly increase. There are no significant changes of standard deviation, apart from scenario B2 in the period 2070-2099, which also suggests a significant increase in the extremes (Fig. 5.3).

o 20

go 10

o 20

go 10

Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep

Fig. 5.4. Streamflow (m3/s) modelling for the Charvak sub-basin for the time slice 2070-2099.

Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep

Fig. 5.4. Streamflow (m3/s) modelling for the Charvak sub-basin for the time slice 2070-2099.

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