Chapter 2 Climate Change Affecting Rice Production

Rice yields in tropical/subtropical Asia exhibit large but opposing sensitivities to minimum and maximum temperatures

“…This difference can be explained by the fact that T max within our sample seldom reached the extremes that cause these negative impacts. For example, fewer than 4% of the observations of T max during the reproductive phase in our sample exceeded the frequently cited threshold of 35°C, above which spikelet sterility becomes common under humid conditions (2,4). Field trials for rice grown under ambient temperatures have reported a positive impact of T max (5), and most controlled-environment studies use 29-30°C as the optimal daytime growing temperature (32).…”

“…Current knowledge is based primarily on field trials and greenhouse experiments. These experimental studies indicate that increased temperature (1)(2)(3)(4) and decreased radiation (1,3,5) can reduce yield, with the impacts varying across the plant's three growth phases (vegetative, establishment to panicle initiation; reproductive, panicle initiation to flowering; ripening, flowering to mature grain). Unresolved issues remain with respect to the relative impacts of temperature during daytime (T max ) vs. nighttime (T min ), potentially confounding impacts of temperature and radiation, and the magnitude of impacts in nonexperimental settings.…”

“…With few exceptions (6,7), most statistical studies on temperature and rice yield have focused on the impact of daily mean temperature (T ave ), despite evidence that that the effects of T min and T max on crop phenological development and physiological processes differ (4). It is well-established that extremely high levels of T max during flowering can drastically reduce rice yield because of spikelet sterility, but recent studies have provided evidence that yield might be more sensitive to T min than to T max in locations where spikelet sterility is rarely observed (8).…”

“…It is well-established that extremely high levels of T max during flowering can drastically reduce rice yield because of spikelet sterility, but recent studies have provided evidence that yield might be more sensitive to T min than to T max in locations where spikelet sterility is rarely observed (8). Rice simulation models began to include T min and T max as separate variables only recently (4). Better understanding of the impacts of temperature at different points in the diurnal cycle is needed, because T min has been rising faster than T max in some important Asian rice-growing countries, including the two largest, China (9) and India (10), and is projected to continue doing so in the future (p 882 in ref.…”

“…A recent review of the impacts of climate change on rice concluded that "the effect of high night temperature is not understood well" (p 75 in ref. 4).…”