Impacts of climate change on rice production in Africa and causes of simulated yield changes

Abstract

This study is the first of its kind to quantify possible effects of climate change on rice production in Africa. We simulated impacts on rice in irrigated systems (dry season and wet season) and rainfed systems (upland and lowland). We simulated the use of rice varieties with a higher temperature sum as adaptation option. We simulated rice yields for 4 RCP climate change scenarios and identified causes of yield declines. Without adaptation, shortening of the growing period due to higher temperatures had a negative impact on yields (-24% in RCP 8.5 in 2070 compared with the baseline year 2000). With varieties that have a high temperature sum, the length of the growing period would remain the same as under the baseline conditions. With this adaptation option rainfed rice yields would increase slightly (+8%) but they remain subject to water availability constraints. Irrigated rice yields in East Africa would increase (+25%) due to more favourable temperatures and due to CO2 fertilization. Wet season irrigated rice yields in West Africa were projected to change by -21% or +7% (without/with adaptation). Without adaptation irrigated rice yields in West Africa in the dry season would decrease by -45% with adaptation they would decrease significantly less (-15%). The main cause of this decline was reduced photosynthesis at extremely high temperatures. Simulated heat sterility hardly increased and was not found a major cause for yield decline. The implications for these findings are as follows. For East Africa to benefit from climate change, improved water and nutrient management will be needed to benefit fully from the more favourable temperatures and increased CO2 concentrations. For West Africa, more research is needed on photosynthesis processes at extreme temperatures and on adaptation options such as shifting sowing dates.

Keywords: Africa; climate change; cold induced sterility; heat induced sterility; irrigated; photosynthesis; rainfed; rice.

Figure 1

CO ₂ and temperature scenarios. (a) Projected changes in atmospheric CO2 concentrations in the 4 RCP scenarios and (b) projected temperature changes averaged over the study sites in the main growing season

Figure 2

Projected changes in maximum temperatures from 2000 (current) to 2070 in RCP scenario 8.5 for rice growing areas in the main growing season

Figure 3

Leaf gross assimilation as affected by various factors in the ORYZA2000 model. The solid lines show the default response curves in ORYZA2000 at 1.5 g N/m² leaf area at two atmospheric CO ₂ contents and two intercepted radiation levels. Average daytime temperature on the x‐axis is calculated as 0.75 × T _max + 0.25 × T _min. The default shows a sharp decline in assimilation above 37°C. The dashed lines (AMAX nondecreasing) show a scenario explored in the current paper to investigate if simulated yield declines were caused by decreasing AMAX above 37°C daytime temperature. The small minimum assimilation rate of 10 kg CO ₂/ha leaf per hour below 10°C and above 43°C, is practically inconsequential

Figure 4

Simulated change in yields in irrigated sites in the “unchanged duration” scenario for RCP scenarios 2.6 (blue) and 8.5 (red). The top pane (a) shows on the x‐axis future spikelet fertility as affected by heat (SFHEAT, 0–1), which is 1 minus the spikelet sterility. In the bottom pane (b) the black line shows part of the trapezoid function of the temperature function with which the maximum assimilation rate AMAX is multiplied (Figure 3). AMAX is optimal (1, here scaled to 0%) from 20 to 37°C. From 37°C to 43°C, the temperature multiplier for AMAX drops to 0 (here −100%). Each dot represents a simulation for a site (53 irrigated sites Africa) in a specific season (main season or off season) and year (1998–2002)

Figure 5

Irrigated rice climate change impact. Simulated changes in two seasons, with adaptation (“unchanged duration”) and without adaptation (“shorter duration”). For the main season and the off season. RCP scenario 8.5, changes 2000 to 2070

Figure 6

Rainfed rice climate change impact. Simulated changes in two seasons, with adaptation (“unchanged duration”) and without adaptation (“shorter duration”). For the main season, for two soil types/landscape positions. RCP scenario 8.5, changes 2000 to 2070