Projected changes in temperature for the Mekong Basin

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An increase in temperature of 0.68 to 0.81 is projected for 2030 over the Mekong basin as a whole (Figure 3.1). The best estimate in of the average increase of temperature over the Mekong basin represented by the median of GCM simulations is 0.79oC. This reflects a change in average temperature from 21.2 to 22.0 oC. The increase in temperature projected for different months ranges from 0.73 oC in October to 0.88 oC in March. Projected increases are generally smaller (< 0.75 oC) for the months of July to November, and more than 0.79 oC for the remaining months. There is some uncertainty in projections for basin temperatures, but all models indicate that temperatures will increase in all months compared with baseline temperatures.

Mekong Basin

16 20 24 28

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

Temperature (o C)

GCM temperature range GCM median temperature

Baseline climatological temperature

Figure 3.1. Baseline (1951-2000) versus future (2030) monthly mean temperature.

3.4.2. Projected changes in temperature for Mekong catchments

The spatial distribution of the response in mean temperature under the most likely climate projections for 2030 indicates a temperature increase of 0.7-0.8oC for the majority of catchments (Figure 3.2). Temperature increases tend to be greater towards the northern part of the basin, with the greatest increase (>1.0 oC) in the coldest Upper Mekong

catchment, and increases from 0.8 to 0.9 oC in catchments of Northern Thailand and Laos.

The smallest increases in projected temperature (0.8 to 0.9 oC) are for the Ban Keng Done and Mukdahan catchments.

Figure 3.2. Spatial distribution of the projected change in mean temperature at 2030 compared with historical (1951-2000) mean temperatures.

The projected seasonal response in average temperature is generally similar across the catchments of the basin, with generally smaller increases in the months from July to November, and larger increases for the remaining cool/cold months (Figures 3.3 to 3.5).

Thus the amplitude in seasonal variation in temperature will tend to be reduced. In all catchments of the basin, the range in projected temperatures is greater for all months than historic figures (Figures 3.3 to 3.5).

The largest most likely increase in monthly temperature by 2030 is in the Upper Mekong where the November temperature is projected to increase by 1.31 oC. Temperature increases are smaller for all other catchments of the basin, and there is less variation between the catchments in temperature increases Projected increases are <1 oC for all months in all other basin catchments (Figures 3.3 to 3.5). The smallest temperature

increases are for the Ban Keng Done catchment, where the largest projected increase in any month is less than 0.8 oC (Figure 3.4).

Upper Mekong

-10 -5 0 5 10

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

Temperature (oC)

GCM temperature range GCM median temperature Baseline climatological temperature

Chiang Saen

10 15 20 25

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

Temperature (oC)

GCM temperature range GCM median temperature Baseline climatological temperature

Figure 3.3. Baseline (1951-2000) versus future (2030) monthly mean temperature for catchments of the Upper Mekong basin: Upper Mekong and Chiang Saen.

Moung Nouy

15 20 25 30

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

Temperature (oC)

GCM temperature range GCM median temperature Baseline climatological temperature

Luang Prabang

15 20 25 30

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

Temperature (oC)

GCM temperature range GCM median temperature Baseline climatological temperature

Ventiane

15 20 25 30

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

Temperature (oC)

GCM temperature range GCM median temperature Baseline climatological temperature

Tha Ngon

15 20 25 30

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

Temperature (oC)

GCM temperature range GCM median temperature Baseline climatological temperature

Nakhon Phanom

20 25 30 35

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

Temperature (oC)

GCM temperature range GCM median temperature Baseline climatological temperature

Mukdahan

20 25 30 35

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

Temperature (oC)

GCM temperature range GCM median temperature Baseline climatological temperature

Ban Keng Done

20 25 30 35

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

Temperature (oC)

GCM temperature range GCM median temperature Baseline climatological temperature

Yasothon

20 25 30 35

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

Temperature (oC)

GCM temperature range GCM median temperature Baseline climatological temperature

Figure 3.4. Baseline (1951-2000) versus future (2030) monthly mean temperature for Moung Nouy, Luang Prabang, Vientiane, Tha Ngon, Nakhon Phanom, Mukdahan, Ban Keng Done and Yasothon catchments.

Se San

20 25 30 35

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

Temperature (oC)

GCM temperature range GCM median temperature Baseline climatological temperature

Kratie

20 25 30 35

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

Temperature (oC)

GCM temperature range GCM median temperature Baseline climatological temperature

Tonle Sap

20 25 30 35

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

Temperature (oC)

GCM temperature range GCM median temperature Baseline climatological temperature

Phnom Penh

20 25 30 35

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

Temperature (oC)

GCM temperature range GCM median temperature Baseline climatological temperature

Border

20 25 30 35

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

Temperature (oC)

GCM temperature range GCM median temperature Baseline climatological temperature

Delta

20 25 30 35

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

Temperature (oC)

GCM temperature range GCM median temperature Baseline climatological temperature Ubon Ratchathani

20 25 30 35

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

Temperature (oC)

GCM temperature range GCM median temperature Baseline climatological temperature

Pakse

20 25 30 35

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

Temperature (oC)

GCM temperature range GCM median temperature Baseline climatological temperature

Figure 3.5. Baseline (1951-2000) versus future (2030) monthly mean temperature for Ubon Ratchathani, Pakse, Se San, Kratie, Tonle Sap, Phnom Penh, Border and Delta catchments.

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