Global cotton production under climate change – Implications for yield and water consumption

摘要

Being an extensively produced natural fiber on earth, cotton is of importance for economies. Although the plant is broadly adapted to varying environments, the growth of and irrigation water demand on cotton may be challenged by future climate change. To study the impacts of climate change on cotton productivity in different regions across the world and the irrigation water requirements related to it, we use the process-based, spatially detailed biosphere and hydrology model LPJmL (Lund–Potsdam–Jena managed land). We find our modeled cotton yield levels in good agreement with reported values and simulated water consumption of cotton production similar to published estimates. Following the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP) protocol, we employ an ensemble of five general circulation models under four representative concentration pathways (RCPs) for the 2011–2099 period to simulate future cotton yields. We find that irrigated cotton production does not suffer from climate change if CO 2 effects are considered, whereas rainfed production is more sensitive to varying climate conditions. Considering the overall effect of a changing climate and CO 2 fertilization, cotton production on current cropland steadily increases for most of the RCPs. Starting from ～65 ?million tonnes in 2010, cotton production for RCP4.5 and RCP6.0 equates to 83 and 92?million?tonnes at the end of the century, respectively. Under RCP8.5, simulated global cotton production rises by more than 50?% by 2099. Taking only climate change into account, projected cotton production considerably shrinks in most scenarios, by up to one-third or 43 million tonnes under RCP8.5. The simulation of future virtual water content (VWC) of cotton grown under elevated CO 2 results for all scenarios in less VWC compared to ambient CO 2 conditions. Under RCP6.0 and RCP8.5, VWC is notably decreased by more than 2000?m 3 ?t ?1 in areas where cotton is produced under purely rainfed conditions. By 2040, the average global VWC for cotton declines in all scenarios from currently 3300 to 3000?m 3 ?t ?1 , and reduction continues by up to 30?% in 2100 under RCP8.5. While the VWC decreases by the CO 2 effect, elevated temperature acts in the opposite direction. Ignoring beneficial CO 2 effects, global VWC of cotton would increase for all RCPs except RCP2.6, reaching more than 5000?m 3 ?t ?1 by the end of the simulation period under RCP8.5. Given the economic relevance of cotton production, climate change poses an additional stress and deserves special attention. Changes in VWC and water demands for cotton production are of special importance, as cotton production is known for its intense water consumption. The implications of climate impacts on cotton production on the one hand and the impact of cotton production on water resources on the other hand illustrate the need to assess how future climate change may affect cotton production and its resource requirements. Our results should be regarded as optimistic, because of high uncertainty with respect to CO 2 fertilization and the lack of implementing processes of boll abscission under heat stress. Still, the inclusion of cotton in LPJmL allows for various large-scale studies to assess impacts of climate change on hydrological factors and the implications for agricultural production and carbon sequestration.