The cropping systems include two tillages components, hand-plowed and no-tillage, and two fertilization rates: low and high nitrogen. A locally adapted rice cultivar was calibrated and validated using a dataset based on experiments conducted over a 6-year period. Daily weather data were generated for a set of 90 virtual years, from to Our results show that no-tillage systems have no advantage for climate change issues. Nitrogen was a major constraint for crops in hand-plowed and no-tillage systems.
We found negative effects of climate change on soil carbon and nitrogen. By contrast, we found positive effects of temperature and increased CO2 on rice growth. The overall effects on rice yields are positive under the most pessimistic climate change scenarios but we demonstrate that the sustainability of these systems is threatened.
Site du Cirad Annuaire des sites du Cirad. Therefore, two qualitative methods were applied to assess model credibility. Firstly, we checked if the model correctly simulated spatial patterns across climatic zones and production systems.
This was indeed the case. Simulated and actual yields were also high in the main season in the highlands of East Africa e. Simulated and actual yields are lower in the rainfed systems, due to drought and interannual variation in simulated rainfed rice yields was larger than that of irrigated rice yields. The second qualitative model credibility check was expert consultation. In the global yield gap atlas GYGA project, credibility of 81 simulated yields for was assessed for eight African countries also included in the current study.
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 unfortunately it did not result in reliable data for quantitative validation.
Model accuracy also depends on quality of the input data. We used the ORYZAv2n14s1 model to identify the main causes of future yield changes under climate change. In the model an elevated CO 2 concentration has an exclusively positive effect on rice productivity. The following two sections describe how we tested these hypotheses. Development is faster at higher temperatures, leading to a shorter growing period and accordingly less time for accumulating biomass, hence lower yields.
To investigate how much of the simulated yield loss was caused by shortening of the growing season we simulated scenarios in which growth duration would remain the same as in the year This analysis serves, firstly, to identify shortening growth duration as a cause of yield decline. Secondly, it can be considered an adaptation option for African rice farmers, showing what would happen if they would gradually replace their current varieties with new varieties that have a higher temperature sum, keeping pace with shortening of the season due to temperature rise.
In the context of climate change, current varieties will have a shorter duration in the future and adapted varieties will have an unchanged duration relative to the baseline year in the future. It should be noted that virtually no experimental data have reported from this temperature range. If model outcomes show great sensitivity of simulated yields to this temperature response, in specific areas, then those areas can be targeted for further experimentation. Potential yields are higher in irrigated systems than in rainfed systems and interannual variability is less in irrigated systems.
Simulated rainfed yields are substantially lower in rainfed upland than in rainfed lowland, which is consistent with lower water availability in the upland soils. Variation in yields is higher for rainfed systems than for irrigated systems, which is consistent with greater risk caused by drought. Yields shown in this table are averaged over 22 irrigated sites in East Africa — , 31 irrigated in West Africa — , 27 rainfed sites in East Africa — and 29 rainfed in West Africa — Yields are shown as potential yield Y p irrigated and water limited yield Y w rainfed , in tonnes dry matter per hectare unmilled rice.
In brackets is the standard deviation showing the interannual and site variability in tonnes dry matter per hectare. Rainfed rice is mostly grown in the wet season; in the central highlands of Uganda and Rwanda with bimodal rainfall patterns two seasons are found. In many parts of the world dry off season irrigated crops yield more than wet main season irrigated crops, due to higher radiation levels in the dry season. Here the opposite was found, with on average lower potential yields in the dry off season.
In West Africa this was caused by reduced assimilation at high temperatures in 16 hot inland irrigation systems along the Niger river Mali, Niger, northern Nigeria, northern Benin and the Benue in North East Nigeria. 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.
This finding suggests that in the future with temperature rise, dry season irrigated rice in Madagascar will become an increasingly attractive option. Average yield decline is lowest in RCP scenario 2. Therefore, it can be concluded that shortening of the growing period is the main cause of projected yield decline and this effect is present in all sites and all growing environments. In the baseline simulations the duration growing period becomes shorter due to temperature rise. For RCP8. For brevity this effect is only shown for RCP8. Rainfed rice is mostly grown in the wet season; in a few sites in the central highlands of Uganda and Rwanda with bimodal rainfall patterns two seasons are found.
Rainfed rice yields increase less than irrigated rice RCP8. In three of four irrigated systems yields increase RCP8. The difference between rainfed and irrigated rice indicates that frequently during the growing season the main production limiting factor is water and not CO 2 and therefore rainfed rice benefits less from CO 2 fertilization. East Africa irrigated rice yields increase as a result of CO 2 fertilization and because temperatures are often below optimum.
In West Africa irrigated rice in the hot dry season yields decrease because of reduced assimilation. Simulations suggested that average heat induced sterility would hardly increase. Apparently stronger transpirational cooling and earlier flowering opening times at elevated temperatures are enough to offset temperature rise, leading to almost unchanged spikelet temperatures at flowering opening time.
Each dot represents a simulation for a site 53 irrigated sites Africa in a specific season main season or off season and year — The table as well as the maps show a gradient of yield decline in West Africa, with most severe yield decline in the hotter northern landlocked countries Mali, Niger and less in the cooler coastal countries of West Africa. In East Africa, all the cooler irrigated systems in the highlands Kenya, Madagascar, Rwanda, Tanzania benefit from climate change.
Thus in Egypt yields do not increase as strongly as in the rest of East Africa which is cooler and do not decrease as strongly as in West Africa which is hotter. Irrigated rice climate change impact. For the main season and the off season. RCP scenario 8. Rainfed rice climate change impact.
Empty spaces mean no simulations were conducted, which in most cases means the combination is absent. Similar tables for the all four scenarios RCP2. This study is the first comprehensive study that addresses the impact of climate change on rice productivity in Africa. Overall, yield decline is found in all scenarios if farmers continue using the current varieties. Small yield increases are predicted if farmers adopt varieties that have a higher temperature sum, thus adapting to shortening of the growing duration induced by temperature increases.
Two main causes of yield decline were identified:.
Decrease in assimilation, but only in the hottest environment, i. And no study so far has identified reduced assimilation at extreme temperatures as a possible cause of future rice yield reductions. Notably, this trapezoid temperature response function uses daily air temperature as the explanatory x variable. Thus much uncertainty still remains. No rice leaf photosynthesis measurements have ever been reported from hotter environments, such as the inland dry season irrigated rice in countries like Mali, Niger, northern Benin and northern Nigeria.
For these countries we are extrapolating with our model into a temperature range where models have hitherto not been tested, which makes our projections more uncertain. Rice models would benefit from testing, comparison and improvement in such environments and testing across multiple environments. Our paper shows the relevance of such research and identifies target areas for such research. We note this is a preliminary conclusion. This suggests also a need for more empirical and modelling research on heat sterility models.
According to von Liebig's law of the minimum De Wit, , crop production is constrained by the most limiting resource. Resources include light, atmospheric CO 2 concentration, soil nutrient supply and water supply. Our simulations suggest that yield increases are possible in most of East Africa, caused by more favourable temperatures and increasing CO 2 concentrations.
According to von Liebig's law, these yield increases will only materialize if CO 2 is more limiting than water and nutrient supply. In line with this, our simulations showed larger yield increases in the East African irrigated systems than in the rainfed systems, because there during parts of the growing season water is more limiting than CO 2. This suggests that to benefit from climate change, East African countries will need to improve water management.
If water and nutrient management are not improved, then yields will increase only little, or not increase. Lobell and Guan, Sultan, Biasutti, Baron, and Lobell argued that many technological interventions are as useful now as in the future and that they should therefore not be mistaken for adaptation options to climate change. They proposed a method to compute how much a technology contributes as a climate change adaptation option, by accounting for how much it would already contribute in the current climate.
If farmers stay with current varieties, irrigation does not help as an adaptation option to climate change: irrigation alone has the same positive effect now and in the future. The combination of irrigation and adapted varieties i. The results raise the question whether in the current climate longer duration varieties might also be a good idea Lobell, There are three arguments against doing so in this particular case.
We found only three recent published country specific studies on climate change on rice in Africa. The combined effects of high temperatures and moisture deficits could critically alter the seasonality and locality of the impact of ENSO on rice production. Cold is relevant because in parts of Africa rice suffers from cold induced sterility and this may decrease in the future with temperature rise. The variance in future temperatures represents inter-model spread and present-day interannual variability. In the past, land policies in the Philippines have favored expansion of production [ 52 ], focusing on increased planting of annual staples [ 53 ].
Firstly, a longer growing period would probably just lengthen the vegetative phase of rice growth, which is often already quite long in the cooler environment of Madagascar. In such situations, longer duration for a sink limited crop would give little yield gain. Secondly, there may be economic objections against longer duration varieties.
If for example a variety with vs. Thirdly, there is the issue of farm planning. Labour availability and length of the growing period of the other crop may be a reason for not wanting to grow varieties with a longer duration, because this might create logistic problems.
For these reasons, we opted not to explore the scenario of adaption of longer duration varieties in the current climate. A number of uncertainties were identified in this study. Firstly the leaf photosynthesis temperature response which we discussed above. Secondly the uncertainty about cold sterility see our discussion in 2. A physiologically sufficiently sophisticated model would not require applying different parameters for the same variety in different regions such as we did in this study.
Further empirical and modelling work is needed in this regard. Thirdly, the uncertainty caused by not accounting for soil fertility in our modelling work. We assumed the response to climate change would be similar under low and high soil fertility conditions. If projected climate change impact is negative then there would be no interaction with soil fertility, because less nutrients are demanded from the soil, so soil nutrient content does not matter.
On the other hand if climate change impact shows increasing potential yields then more nutrients will be demanded from the soil. This extra nutrient uptake will be more easily met on the more fertile soils or if additional fertilizer is applied. In this scenario climate change impact would be positive only on fertile soils and be neutral on infertile soils, a three way positive interaction between soil fertility, CO 2 fertilization and crop yield.
Investigation of soil fertility interactions was impossible because it would require high resolution soil fertility mapping and validation of a rice model for nutrient balances, something which was beyond the scope of this paper. Clearly studying such interactions would be most relevant for East Africa, where our simulations show increasing potential yields. The fourth uncertainty is that of possible change in rainfall patterns. This comes on top of our assumptions on groundwater depth, for which also no high spatial and temporal resolution African datasets are available.
Altogether we deem these uncertainties too large to allow for meaningful analyses of their effects on future rainfed rice yields. Relatively much awareness exist of the above four uncertainties in the scientific community. There are two uncertainties of which we are aware but for which we are even more uncertain than those listed above. These are future effects of climate change on salinity and on cyclone frequency. The number of unknowns is too large to allow for quantitative estimation of how far sea water intrusion will increase and how this will affect mangrove rice areas.
Rice in Africa is only affected by cyclones in Madagascar, one of the largest rice producers of Africa. Thus there are a number of additional negative climate change effects that can be anticipated but for which the magnitude of changes as well as the possible impacts are still very uncertain. Overall, negative impacts of climate change on rice yields in Africa are shown in all scenarios if farmers stay with current varieties. Predominantly positive effects are observed if farmers adopt varieties with a higher temperature sum, keeping pace with shortening of the growing duration due to temperature.
Irrigated rice yields in the hot dry season of West Africa will reduce significantly due to reduced photosynthesis. For East Africa to benefit from climate change, improved water management and possibly also soil fertility management will be needed in combination with gradually replacing current varieties with varieties with a higher temperature sum. In West Africa, more research is required to improve our knowledge on photosynthesis processes during extreme temperatures and research is needed on adaptation options for rice farmers such as shifting sowing dates more into the cold dry season.
We thank dr.
Sander C. Impacts of climate change on rice production in Africa and causes of simulated yield changes. Glob Change Biol. National Center for Biotechnology Information , U. Global Change Biology. Glob Chang Biol. Published online Dec Pepijn A. Zwart 1 , 3. Sander J. Author information Article notes Copyright and License information Disclaimer. Corresponding author. Email: gro.
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. This article has been cited by other articles in PMC. Associated Data Supplementary Materials. Abstract This study is the first of its kind to quantify possible effects of climate change on rice production in Africa. Keywords: Africa, climate change, cold induced sterility, heat induced sterility, irrigated, photosynthesis, rainfed, rice.
Data 2. Table 1 Rice harvested areas and number of simulation sites for countries in this study. Open in a separate window. Especially in irrigated systems double rice cropping is found. Figure 1. Figure 2. Weather data For selected sites we used daily weather data from the AgMERRA dataset, which contains daily weather data for crop modelling from to at 0.
Cold sterility Cold is relevant because in parts of Africa rice suffers from cold induced sterility and this may decrease in the future with temperature rise. Model credibility A number of steps were taken to establish model credibility. Causes of yield decline We used the ORYZAv2n14s1 model to identify the main causes of future yield changes under climate change.
If heat induced sterility increases or if respiration increases, then yield can decrease. Phenology Development is faster at higher temperatures, leading to a shorter growing period and accordingly less time for accumulating biomass, hence lower yields. Figure 3. Table 3 Baseline crop potential yields and variability. Figure 4. Figure 5. Figure 6. Table 5 Simulated changes in rice yield averaged by country and by environment. Africa Country RCP8. Main outcomes This study is the first comprehensive study that addresses the impact of climate change on rice productivity in Africa.
Two main causes of yield decline were identified: Shortening growing period in all growing environments across Africa, and Decrease in assimilation, but only in the hottest environment, i. East Africa: opportunities According to von Liebig's law of the minimum De Wit, , crop production is constrained by the most limiting resource. Table 6 Rice yields in Madagascar in current and future climate, with and without adaptations.
In rainfed upland systems the combination of irrigation and adapted varieties unchanged duration contributes as a climate change adaptation option [ Uncertainties A number of uncertainties were identified in this study. Synthesis Overall, negative impacts of climate change on rice yields in Africa are shown in all scenarios if farmers stay with current varieties.
Effects of modelling detail on simulated potential crop yields under a wide range of climatic conditions. Ecological Modelling , , — Food crop production in Nigeria. Potential effects of climate change. Climate Research , 32 , — Effect of uncertainties in scenarios and crop models on impact assessment.
Climatic Change , 52 , — Flood projections within the Niger River Basin under future land use and climate change. Science of the Total Environment , , — Constraints on future changes in climate and the hydrologic cycle. Nature , , — Amsterdam: Elsevier. Part 1. Rice variety duration, sowing date and inclusion of mungbean. Field Crops Research , , 68— International Journal of Agricultural Sustainability , 13 , 87—