Modelling climate change impacts on wheat (Triticum aestivum) and rice (Oryza sativa) and their pests using CLIMEX: A case study of Iraq

Abstract

<p>Wheat (<i>Triticum aestivum</i>) and rice (<i>Oryza sativa</i>) are cereal crops that are cultivated worldwide for their economic benefits and as part of the essential diet for people. However, climate change affects the distribution of these crops, as well as the pests that are associated with them, introducing a serious threat to plantation globally. This study uses CLIMEX modelling software to illustrate the climatic suitability of the distribution of six species in the current and potential future periods—2030, 2070, and 2100, respectively—under two Global Climate Models (GCMs), CSIRO-Mk3.0 (CS) and MIROC-H (MR), with A1B and A2 climate scenarios. According to the research outcomes, there is a similar general trend that all species are facing degradation in the southern hemisphere, while in the northern hemisphere climate suitability is to increase noticeably in the future. The main aim of conducting this study is to model the variability in the projections of climate change impacts on two crops, four insect pests globally, and in Iraq as a case study. </p> <p>The first study models the wheat crop and indicates that the suitable climatic areas in the southern hemisphere, such as Australia, for the distribution of this crop are expected to contract by the end of this century. However, some of the currently unsuitable or marginal areas are going to become climatically suitable under future climate scenarios, especially in North Canada and Europe, although further expansion inland could also occur. Heat and dry stresses, as abiotic climatic factors, are to play an important role in wheat distribution in the future. </p> <p>The second study models a particular wheat insect pest, the sunn pest (<i>Eurygaster integriceps</i>), as a pest of economic importance. It is found throughout Western Asia and Eastern Europe in dry to temperate climatic areas. Its potential global range is expected to extend further polewards, between the latitudes 60°N and 70°N. Northern Europe and Canada are also going to become suitable areas for these pests as cold stress boundaries recede. However, the current highly suitable areas for these pests, such as South Africa and central Australia, are going to contract as precipitation is projected to substantially decrease with increased heat stress. </p> <p>The third study simulates models for the potential distribution of a second wheat insect pest, the greenbug (<i>Schizaphis graminum</i>). The results clarify that the climatic areas favourable for this pest are subtropical to temperate. With climate change, the currently suitable and highly suitable areas in the northern hemisphere are expected to expand to higher latitudes in the future. At the same time, in the southern hemisphere, where this pest’s living areas are already in the high temperature ranges, the occurrence of this pest species is going to contract as their highest limits of heat stress are exceeded./p> <p>The fourth study overlays these wheat pests onto optimal wheat cultivation areas to illustrate the potential risk levels of wheat pest invasion in the future. The potential distributions of the three aforementioned species forecast a substantial increase, especially towards the end of the 21st century in the northern hemisphere. Therefore, these wheat pests could become a more widespread problem in countries located in this hemisphere and the risk level is expanding. In the southern hemisphere, on the other hand, the risk level for these pests is going to decrease along with climatic suitability. However, some areas are expected to have variable risk levels. </p> <p>The fifth study models the second crop—rice. Its cultivation areas are limited by cold stress in northern countries and dry stress in Africa, inland Australia, parts of Asia, as well as North and South American continents. Irrigation scenarios in the simulations are important for maintaining cultivation over long time periods. Potential increases are seen in higher latitude cultivation areas with decreases in lower latitude areas; the climate effect is more pronounced under the CS than the MR model and the degradation in climate suitability under A2 scenarios is much greater under both GCMs. </p> <p>The sixth study models two pests that affect rice—the yellow rice stem borer (<i>Scirpophaga incertulas</i>) and the striped rice stem borer (<i>Chilo suppressalis</i>). They are currently distributed throughout the tropical, subtropical, and temperate regions of Asia, Europe, and Australia. Rice stem borers show potential to threaten wide areas of the northern hemisphere in the future that currently have an unsuitable climate and to extend their range pole-ward through Europe and Asia. Some parts of southern Australia could also develop conditions that are more favourable for them under the MR climatic scenario, while northern Australian regions could become less suitable by the end of this century. </p> <p>The seventh study investigates the risk levels posed through an overlay of two rice pests onto optimal rice cultivation areas. These pests are likely to become more aggressive and invasion risk levels in the northern hemisphere are increased. The climactic suitability for these pests is expected to expand to northern latitudes for<i> C. suppressalis</i> and <i>O. sativa</i>, and for <i>S. incertulas</i>. The current cold stress that prevents the establishment of these species in the northern regions is going to decrease due to elevated temperature towards the year 2100. Heat and dry stresses are the main reasons for their unsuitability outputs in the southern hemisphere. </p> <p>The last study focuses on the impacts of climate change in Iraq based on previous global modelling studies presented in this research using results zoomed to a country level. Significant reduction in climate suitability is projected for both the wheat and rice crops, as well as for their accompanying pests, through the 21st century. Consequently, this reduction would also decrease the pest invasion risk. </p> <p>Overall, the findings of the studies presented in this paper are important with respect to their biosecurity implications since they discuss the possibility of pest invasions using crop prospective cultivation areas that are affected by climatic conditions. Current study results could help in producing more comprehensive risk assessment of economic impact pests on wheat and rice productivity to their potential distributions, providing supportive information for agricultural management practices in order to prepare strategic plans and to avoid possible economic damage posed by future expansion of the pest population due to climate change. </p>