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.
Highlights
| MATERIALS AND METHODSThe ORYZA2000 crop growth model is a point-based model, i.e. it is used to simulate rice yields for specific sites and does not model landscape hydrology
For the seven cooler irrigation systems in the coastal regions we did find higher simulated yields in the dry season (Mauritania: Rosso, Senegal: Ndiaye and Fanaye, Gambia: Sapu, Ghana: Yendi, Nigeria: Bida and Lokoja). This finding suggests that much of the dry season irrigated rice in the Sudano Sahel zone is around the 37°C tipping point (Figure 3) for which with further temperature rise dry season rice yields will decrease
In East Africa irrigated systems simulated dry season yields were lower than wet season yields because most of the simulations for dry season irrigation systems were for sites in the cold dry winter season in Madagascar, where cold is negatively affecting potential rice yields
Summary
The ORYZA2000 crop growth model is a point-based model, i.e. it is used to simulate rice yields for specific sites and does not model landscape hydrology. At the Africa Rice Centre, where the authors of this paper are employed, improvements have been made on heat sterility, cold sterility and phenology (Van Oort, De Vries et al, 2015) The latter are of particular relevance in the context of climate change studies. We found that simulations with decreasing relative humidity (as in the original model) led to large overestimation of future drought To correct for this effect we incorporated a function that maintains the same level of RH between current climate conditions and climate change scenarios by adjusting the actual vapour pressure as needed. Country agronomists checked sowing dates, crop duration, yield levels and spatial patterns within their countries This lead to various model improvements and this iterative process was continued until credible results were obtained for all sites, but it did not result in reliable data for quantitative validation. If model outcomes show great sensitivity of simulated yields to this temperature response, in specific areas, those areas can be targeted for further experimentation
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