Assessment of impact of climate change on rice and wheat yield in sub humid climate of Bihar

The climate sensitivity of agriculture is uncertain, as there is regional variation of extreme temperature and rainfall, the crop and cropping system, soils and management practices.Inter-Governmental Panel on Climate change (IPCC) Fifth Assessment Report concludes that increasing numbers of warm days and decreasing numbers of cold days have been observed, with the warming trend continuing into the new millennium (IPCC 2014).General Circulation Models (GCMs) and Special Report on Emission Scenarios (SRES), show that higher temperatures will lead to lower rice yields as a result of shorter growing periods. However, carbon dioxide (CO 2 ) fertilization may at least in part offset yield losses in rice and other crops. In the Indo-Gangetic Plains of South Asia there could be a decrease of about 50% in the most favourable and high-yielding wheat area as a result of heat stress at two times CO 2 (IPCC 2014). Elevated CO 2 besides affecting the crop also affects the environment, which in turn may either beneficial or damaging effect on agricultural production (Rosenzweig et al., 1998). Changes in temperature play a crucial role in determining crop productivity (Fiscus et al., 1997). Decline in potential yield of wheat and rice is linked to negative trend in solar radiation and an increase in minimum temperature in the Indo-Gangetic Plains of India (Pathak et al., 2003). With subsequent rise in temperature reduced the yield of wheat and enhanced CO 2 was unable to counter balance the decline in wheat yield (Abdul Haris et al., 2013). Decision support systems (DSS) or crop models provide a way, where the relative effects of these variables on crop growth and yield can be studied in particular combinations on regional basis. The present study deals with the effects of climate change on kharif and rabi season crops (Rice and wheat) for Bihar which might help to adopt suitable farming techniques to maximise agricultural production in this high potential region. It also provides insights into possible changes in the cropping pattern and adaptation options for future.

The climate sensitivity of agriculture is uncertain, as there is regional variation of extreme temperature and rainfall, the crop and cropping system, soils and management practices.Inter-Governmental Panel on Climate change (IPCC) Fifth Assessment Report concludes that increasing numbers of warm days and decreasing numbers of cold days have been observed, with the warming trend continuing into the new millennium (IPCC 2014).General Circulation Models (GCMs) and Special Report on Emission Scenarios (SRES), show that higher temperatures will lead to lower rice yields as a result of shorter growing periods. However, carbon dioxide (CO 2 ) fertilization may at least in part offset yield losses in rice and other crops. In the Indo-Gangetic Plains of South Asia there could be a decrease of about 50% in the most favourable and high-yielding wheat area as a result of heat stress at two times CO 2 (IPCC 2014). Elevated CO 2 besides affecting the crop also affects the environment, which in turn may either beneficial or damaging effect on agricultural production (Rosenzweig et al., 1998). Changes in temperature play a crucial role in determining crop productivity (Fiscus et al., 1997). Decline in potential yield of wheat and rice is linked to negative trend in solar radiation and an increase in minimum temperature in the Indo-Gangetic Plains of India (Pathak et al., 2003). With subsequent rise in temperature reduced the yield of wheat and enhanced CO 2 was unable to counter balance the decline in wheat yield (Abdul Haris et al., 2013). Decision support systems (DSS) or crop models provide a way, where the relative effects of these variables on crop growth and yield can be studied in particular combinations on regional basis. The present study deals with the effects of climate change on kharif and rabi season crops (Rice and wheat) for Bihar which might help to adopt suitable farming techniques to maximise agricultural production in this high potential region. It also provides insights into possible changes in the cropping pattern and adaptation options for future.

MATERIALS AND METHODS
Bihar is located in the alluvial plains of India and is situated between 24 0 N and 27 0 N, 83 0 E and 88 0 E with a height of 52 m amsl having normal rainfall of 1243.7 mm. Four different station stations were selected representing different zones (Pusa zone I; Purnea zone II; Sabour zone III A; Patna zone III B).Daily data for air temperature and rainfall from four representative centres were collected for the period 1955-2010 for Pusa and Sabour and 1969-2010 for Patna and Purnea. Meteorological, crop and soil data used for the simulation studies were collected from India Meteorological Department, Pune; Rajendra Agricultural University, Pusa and Bihar Agricultural University, Sabour.   . Further the different scenarios were given for 2020, 2050 and 2080 respectively, as incremental variable scenarios have the capacity of capturing a wide range of possible changes in the near future.

Change in yield of rice and wheat crop due to climate change
Simulated yield of rice in different scenario decreased the yield in all the periods. This decrease was in the range of 1.1-9.2 %, 6.1-13.2 %, 19.1-22.2 % for 2020, 2050 and 2080 respectively for all the stations (Table 3). Maximum decrease in yield was observed in Patna for 2020 and 2050 but in 2080, it was maximum in Purnea.These results are in line with those of other researchers. For instance, Peng et al.(2004) observed that yield of rice decreased by 10 % for every 1 0 C rise in growing season T min .
Simulated yield of wheat decreased from the baseline in 2050 and 2080 to3.5-14 %, 13-20 %, 18.7-35.4 % and 21.1-37.9 % for Pusa, Purnea, Sabour and Patna respectively. Simulated yield was also decreased for 2020 by 5 %, 3.7 % and 11 % for Purnea, Sabour and Patna respectively.A decline of 0.45 tonne ha -1 in wheat yield, with increase in temperature from 0.5 0 C to 1.5 0 C has been reported by Kalra et al.(2003). The impact of climate change was more on wheat than rice. This may be ascribed to the increased projected T min and T max and decreased rainfall in the months of Feb to March synchronizing reproductive and grain development stages of wheat. All these conditions reduce   both duration to anthesis and to maturity, leading to poor grain fill in wheat (Arora et al. 1998). Moreover, at high temperature, energy is lost through the process of transpiration by the plant and reduced energy results in poor grain formation and yield. Such effects are less in rice because of relatively lower temperature at maturity and these may not aggravate in future as the projected temperature rise is also less. In the present study, a strong correspondence between reduction in yield and shortening of crop duration under higher temperature was observed in scenarios.

CONCLUSION
The study indicates losses in the yield of rice and wheat with subsequent rise in temperature. However, the percentage decline was more in zone II and III B in case of rice, probably due to more decline of rainfall in future. In case of wheat, decline in yield was more in zone III A and III B, probably due to more increase of minimum temperature in these zones. Notwithstanding these uncertainties, climate change will drive reductions in crop yield. Adaptation options, such as adopting new agronomic practices and delineating favourable areas for rice and wheat production, need to be looked into for sustainability of food security in this region.