Assessment of climate change impact on wheat crop using MarkSim GCM in Varanasi, Uttar Pradesh

GFLD-CM3 model was used to generate weather data under RCPs scenario i.e. RCP 2.6, 4.5, 6.0 and 8.5 for years 2010, 2035, 2065 and 2095 for Varanasi, Uttar Pradesh. The generated data were used to assess the impact of climate change on phenology and yield of wheat crop using CERES-Wheat model. The results revealed that the impact climate change hastened reproductive stages (anthesis, maturity) and decreased yield in all scenarios. The impact was highest under RCP 8.5. Days to antheis and days to maturity were projected to reduce by 22 days and 24 days, respectively in 2095 whereas, grain yield decreased by 61.0 per cent.

from 2010-2095 (Jones and Thornton, 2013); average data of 99 replications of GFLD-CM3 model, with a spatial resolution of 1.2587 × 2.5 (latitude by longitude) was selected. Data were downloaded in DSSAT friendly format for RCP 2.6, 4.5, 6.0 and 8.5for 2010, 2035, 2065 and 2095. The generated weather data of year 2010 with RCP 2.6, 4.5, 6.0 and 8.5 were chosen as baseline for assessment of climate change impact in future years (2035, 2065 and 2095).
The CERES-wheat model embedded in DSSATv4.6 (Hoogenboom et al., 2015) was used to assess climate change impact on yields of wheat crop of Varanasi district of Uttar Pradesh state, India. The corresponding daily weather and soil data (25º182 north latitude, 83°102 east longitude and 76 meter above mean sea level) were collected from Agriculture Research Farm, Banaras Hindu University (BHU), Varanasi. Calibrated and validated genetic coefficients for cultivar HUW 510 by Patel et al. (2017) has been adopted for simulation.

Climate change and variability at Varanasi
For assessment of climate change and variability, 30 years (1981 to 2010) weather data of Varanasi was analyzed and projected for years i.e. 2010, 2035, 2065 and 2095 (Table 1). The maximum temperature was found to increase from 0.5°C to1.9°C, whereas, minimum temperature increased from 0.5 to 2.0°Cfor projected years 2010 to 2095. Solar radiation and rainfall were projected to decrease from 1.4 to 5.5 MJm -2 day -1 and from 141.5 to 542 mm, respectively.

Impact of climate change on phenology of wheat crop
The days to anthesis and days to maturity simulated by the CERES-Wheat model under different RCP scenario in different years 2010,2035, 2065 and 2095 presented in Fig. 1 revealed that the duration would be shorten under all scenarios (RCP 2.6, 4.5, 6.0 and 8.5) and also with years. Upto 2035, there is not much difference, but there after sharp decline in duration of both days to anthesis and maturity is observed under RCP 6.0 and RCP 8.5.The highest decrease was under RCP 8.5 in 2095.In all scenarios, increased maximum and minimum temperature hastening on anthesis and maturity, thereby decreasing the length of the life cycle which shorten the reproductive period resulting in lower grain yield (Menzel et al., 2006).

Impact of climate change on wheat yield
Changes in grain yield of wheat were evaluated by comparing the future wheat yields to the baseline yields of projected year of 2010 with its scenario, and then by stating the change. The effect of climate change on wheat production were studied for projected years i.e. 2035, 2065and 2095 and were compared with that simulated for 2010. The maximum yield decrease was observed in the scenario RCP 8.5, which ranged from -23 to -61 per cent.These results show RCP 8.5 as the most resilient scenario and RCP 2.6 as least resilient scenario to climate change. Projected year 2035 was the least vulnerable and on 2095 the most vulnerable under the all emission scenario (Welikhe et al.,2016). Yadav et al.,(2015) also reported decrease in wheat grain yield with increase in temperature.

CONCLUSIONS
It can be concluded that climate change could potentially result not only in shortening the duration of wheat crop but also in decreasing wheat yields in Varanasi region. Maximum grain yields were projected to decrease under RCP 8.5 in all years with extreme being observed at the end of the century.