Abstract
Global warming is predicted to increase in the future, with detrimental consequences for rainfed crops that are dependent on natural rainfall (i.e. non-irrigated). Given that many crops grown under rainfed conditions support the livelihoods of low-income farmers, it is important to highlight the vulnerability of rainfed areas to climate change in order to anticipate potential risks to food security. In this paper, we focus on India, where ~50% of rice is grown under rainfed conditions, and we employ statistical models (climate envelope models (CEMs) and boosted regression trees (BRTs)) to map changes in climate suitability for rainfed rice cultivation at a regional level (~18×18km cell resolution) under projected future (2050) climate change (IPCC RCPs 2.6 and 8.5, using three GCMs: BCC-CSM1.1, MIROC-ESM-CHEM, and HadGEM2-ES). We quantify the occurrence of rice (whether or not rainfed rice is commonly grown, using CEMs) and rice extent (area under cultivation, using BRTs) during the summer monsoon in relation to four climate variables that affect rice growth and yield namely ratio of precipitation to evapotranspiration (PER), maximum and minimum temperatures (Tmax and Tmin), and total rainfall during harvesting. Our models described the occurrence and extent of rice very well (CEMs for occurrence, ensemble AUC=0.92; BRTs for extent, Pearson's r=0.87). PER was the most important predictor of rainfed rice occurrence, and it was positively related to rainfed rice area, but all four climate variables were important for determining the extent of rice cultivation. Our models project that 15%–40% of current rainfed rice growing areas will be at risk (i.e. decline in climate suitability or become completely unsuitable). However, our models project considerable variation across India in the impact of future climate change: eastern and northern India are the locations most at risk, but parts of central and western India may benefit from increased precipitation. Hence our CEM and BRT models agree on the locations most at risk, but there is less consensus about the degree of risk at these locations. Our results help to identify locations where livelihoods of low-income farmers and regional food security may be threatened in the next few decades by climate changes. The use of more drought-resilient rice varieties and better irrigation infrastructure in these regions may help to reduce these impacts and reduce the vulnerability of farmers dependent on rainfed cropping.
Highlights
Global temperatures rose above pre-industrial levels by +0.85 °C in the last century, and are predicted to exceed + 2 °C this century (RCP 8.5 scenario; IPCC, 2013)
Climate envelope models (CEMs) tended to predict rainfed rice in more cells than those where there were observed presences (Fig. 2a) in India, implying that rainfed rice cultivation is restricted by non-climatic factors not included in CEMs
Rainfed food production systems are highly dependent on climate and our study maps the locations where the production of rainfed rice is at risk from future climate change
Summary
Global temperatures rose above pre-industrial levels by +0.85 °C in the last century, and are predicted to exceed + 2 °C this century (RCP 8.5 scenario; IPCC, 2013). Higher temperature and increased rainfall variability will reduce yields of major crops such as maize, wheat and rice (Sage et al, 2015; Lobell et al, 2011) (there is evidence that climate change has already begun to reduce yields (Lesk et al, 2016)) in spite of the benefits for plants from increased atmospheric CO2 (Hasegawa et al, 2013). Rice is one of the major crops grown and consumed in rainfed areas, and rainfed cultivation accounts for about 25% of global rice production. Due to its dependence on climate, rainfed rice cultivation is vulnerable to changes in temperature and rainfall. Warm temperature (optimal range 20 °C–30 °C) and high rainfall (optimal range 1500 mm–2000 mm) (http://ecocrop.fao.org/) generally increase growth rates of rice plants, and yield (Yoshida, 1981). On the other hand, reduces plant transpiration rates and may result in leaf rolling and drying, reduction in leaf expansion rates and plant biomass, immobilisation of solutes and increased heat stress of leaves (Jagadish et al, 2010; Van Oort et al, 2011)
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