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Chapter Six6 Crop yield projectionsIn this chapter the yields of rice and wheat in Bhutan are projected using the crop modelspresented in Chapter 4 (model 4.1). The model will be driven by the seasonal mean ofcalibrated PRECIS daily mean temperatures presented in Chapter 5.6.1 RiceThe average measured annual yield of rice in Bhutan from 1990 to 2010 is 0.96 tonne/acre.Table 6.1 shows the average annual rice yield in the period 2030 to 2050 projected by thestatistical yield model (refer to Table 4.4) driven by three sets of daily mean temperatures:uncalibrated model temperature, BC calibrated and CF calibrated temperature. Both BC andCF calibrated mean temperatures give an increase in rice yield.Table 6-1 Projected average annual rice and wheat yields (tonne/acre) using PRECISprojected mean temperature for the period 2030 to 2050. Results using raw PRECISprojections and projections calibrated by BC and CF are shown.CropMeanobserved yield(1990-2010)Mean projected yield(2030-2050)Raw model BC CFRice 0.96 -1.43 1.43 1.57Wheat 0.52 0.06 0.78 0.79Figure 6.1 (a) shows how well the statistical crop yield model simulates present rice yieldwhich is shown by the blue line. The model fails to capture the peak rice yield in 2008 andlow rice yield in 1994. However, it can be seen that model captures the general increasingtrend in rice yield quite well.For the period 2030 to 2050, the average projected rice yield by BC calibrated temperatures is1.43 tonne/acre which is 40 % higher than the observed yield (Table 6.1). Figure 6.1 (b)shows the corresponding time series of projected annual rice yield with the 95 % confidence44