Climate Change Projections

Meteorological conditions, such as temperatures and rainfall, have a direct impact on water resources in the basin. Looking at trends in the past can be useful as a first indicator of what possible consequences climate change might have on water resources and, consequently, on agriculture, environment and domestic and industrial water use (Morrison et al., 2000).

As was pointed out earlier, most of the water resources in the basin originate from upper sub-basins (mainly Plasjan sub-basin). Records from the Damaneh Freidan station are a good indicator for the climatic conditions and for climate change in these areas because of its high altitude (2340 m). Figure 6.2 shows mean annual temperatures with a linear trend line analysis. For this station and other stations in the vicinity, the mean annual temperature increase is 0.03-0.05°C/year, although for a few stations in the basin this upward trend was not observed.

From the seven available GCM projections in the IPCC (Intergovernmental Panel on Climate Changes) data set, the Hadley GCM has been selected to be used for further analysis. The A2 and B2 projections based on the most recent IPCC emission scenarios, the so-called SRES (Special Report on Emission Scenario), will be used for two time slices 2010-2039 and 2070-2099.

The Hadley GCM projections are based on grid cells of 2.5° X 3.75° and were downscaled to 0.5° X 0.5° grid using method 2 described in Chapter 2. Subsequently, these projections were transferred in such a way that the main statistical properties of historical measured data match the GCM outputs. For this, the 1972-1990 observed and modelled temperature and precipitation data were used to derive adjustment factors that were subsequently applied to the future projections (2010-2039 and 2070-2099).

Results of applying the above methodology reveal that according to the Hadley GCM projections, the Zayandeh Rud Basin will not experience significant changes in meteorological variables for the first period 2010-2039. However, for the second period 2070-2099, the basin will face more drastic changes. According to the A2

Table 6.2. Statistical parameters of rainfall, mean temperature and discharge according to climate change scenarios.

Statistical

Rain

Temperature

Q

Rain

Temperature

Q

Period

parameter

(mm)

(°C)

(m3/s)

(mm)

(°C)

(m3/s)

1971-2001

AV

1458

10.0

45

sd

371

0.9

14

MAX

894

24.8

289

MIN

0

-7.7

6

Scenarios

A2

A2

A2

B2

B2

B2

2010-2039

AV

1470

11.0

44

1427

11.1

45

sd

538

0.9

31

361

0.6

34

MAX

809

27.5

166

632

27.1

170

MIN

0

-6.4

16

0

-3.5

1

2070-2099

AV

1224

14.6

43

1309

13.2

43

sd

377

1.1

32

442

0.6

40

MAX

776

31.2

220

521

30.4

253

MIN

0

-5.0

10

0

-2.5

6

scenario, mean annual temperature is expected to increase by about 4.5°C and mean annual rainfall depth to decrease by 234 mm. Under the B2 scenario, the temperature increase is 3.2°C and rainfall decrease is 149 mm over the total period 2070-2099 (Table 6.2).

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