Chiang Rai Udon Thani

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5.2 Change in temperature pattern

5.2.1 Chiang Rai

The monthly variation of Tmax, Tmin and mean T during hot weather season March to May and cold weather season Dec to Feb is shown in Figure 5.19 and Figure 5.20 respectively for Chiang Rai. Figure 5.19. Monthly mean temperature variation during hot weather season March to May from 1980 to 2008 over Chiang Rai. a Maximum temperature, b Minimum Temperature and c Mean Temperature. The linear trend line for April is plotted Source: Thailand Meteorological Dept. and Analysis 63 Figure 5.20. Monthly mean temperature variation during cold weather season December to February from 1980 to 2008 over Chiang Rai. a Maximum temperature, b Minimum Temperature and c Mean Temperature. The linear trend line for December is plotted Source: Thailand Meteorological Dept. and Analysis 64 It is seen from Figure 5.19 and Figure 5.20 that the maximum temperature in summer March to May is decreasing but the minimum temperature in summer is increasing. On the other hand during the winter season all the three temperatures Tmax, Tmin and mean T are indicating increasing trend. Thus, summer nights and winters are becoming more warmer and a clear indication of climate change in recent time. The same pattern is also reflected with highest Tmax in summer April and lowest Tmin in winter Dec as shown in Figure 5.21. 15 20 25 30 35 40 45 198 198 2 198 4 198 6 198 8 199 199 2 199 4 199 6 199 8 200 200 2 200 4 200 6 200 8 Year E x tre m e T m ax A p r 5 10 15 E xt rem e T m in D ec Apr Ext. Tmax Dec Ext. Tmin Linear Apr Ext. Tmax Linear Dec Ext. Tmin Figure 5.21. Monthly mean extreme maximum temperature highest Tmax variation during April and monthly mean extreme minimum temperature lowest Tmin during December over Chiang Rai Source: Thailand Meteorological Dept. and Analysis

5.2.2 Udon Thani

The trend of Tmax, Tmin and mean T during summer and winter is shown in Figure 5.22 and Figure 5.23 respectively. The trend in Tmax during summmer Mar-May and Tmin during winter Dec-Feb shows increasing trend over Udan Thani as shown in Figure 5.22a and Figure 5.23b respectively. It is also seen from Figure 5.23a and Figure 5.23c that the Tmax during winter and also the mean temperature during winter is increasing. Thus, summer days and winters days nights are becoming more warmer and a clear indication of climate change in recent time and have the potential of increasing heat wave frequency. The same pattern is also reflected with highest Tmax in summer April and lowest Tmin in winter Dec 65 Figure 5.22. Monthly mean temperature variation during hot weather season March to May from 1980 to 2008 over Udon Thani. a Maximum temperature, b Minimum Temperature and c Mean Temperature. The linear trend line for April is plotted Source: Thailand Meteorological Dept. and Analysis 66 Figure 5.23. Monthly mean temperature variation during cold weather season December to February from 1980 to 2008 over Udon Thani. a Maximum temperature, b Minimum Temperature and c Mean Temperature. The linear trend line for December is plotted Source: Thailand Meteorological Dept. and Analysis 67

5.2.3 Hat Yai