Assessing the impact of climate variability on maize yields in the different regions of Ghana—A machine learning perspective

such as temperature, precipitation, sunshine, humidity, carbon dioxide (CO2), water vapor, rainfall, and greenhouse gases. Although crop yield can be impacted by climatic variables including rainfall, solar radiation, and wind speed [2, 3], precipitation, temperature, and car- bon dioxide (CO2) are seen as the most influential climatic variables on crop yield [4, 5]. Crop production is hampered by low temperatures [6] and crop yields are significantly affected by high temperatures [7]. Similarly, high precipitation, which leads to flooding, damages crops [8], and low precipitation, which leads to drought, damages crop as well [9]. Therefore, any variations on these climate variables may also have a major impact on the agricultural sector [10]. Agriculture is significant to Ghana’s economy and livelihoods, hence understanding the influence of climate variability on agricultural production is critical. Maize production is one of the most significant agricultural products, ranking third place behind rice and wheat in terms of production of cereal crops in the world [11]. In Ghana, maize is a staple crop and con- tributes to most of the agricultural production and consumption in the country. According to research, Ghana produced more than 2.9 million metric tons of maize in 2019, the most since 2010, and 3 million metric tons of maize in 2020, continuing a rising trend that has been evi- dent since 2016 [10]. Maize is grown in all the country’s agro-ecological zones, and it is fre- quently grown by smallholder farmers in rain-fed conditions [12]. As a result, any aggravation

of climate-related factors, such as drought, altered precipitation patterns, and heat stress, is accountable for some of the major issues with maize production in Ghana. The results, how- ever, vary by zone. Ghana has six main agro-ecological zones, which are the Guinea savannah zone, Sudan savannah zone, transitional zone, deciduous forest zone, coastal savannah zone, Rain Forest zone [12]. These agro-ecological zones can be grouped into four subgroups [13] based on maize yield in Ghana (i.e., Transitional Zone, Rain Forest Zone, Guinea Savannah Zone, and Coastal Savanna Zone). Temperature and sunshine are likely to have major impact on maize yield in the Guinea savanna zone since they are the hottest zones in the country [14], and precipitation is also likely to have a major impact in the rain forest zone and the coastal savanna zone [10, 15]. Moreover, average temperature is likely to have a major impact in the transitional zone [10]. The impact of climate change on cereal harvests, such as wheat, rice, and maize, has been extensively studied in Asia [16–20] and North America [21–23]. However, there are limited studies in sub-Saharan Africa, especially considering their regional differences, which is of great concern given the region’s high dependence on agriculture for food security and eco- nomic development. Given the dependency of maize yield on rainfall in many parts of the African continent, Gachene et al. [24] emphasized the vulnerability of cereal yields in the sub- Saharan regions. They reviewed numerous elements, such as extreme weather events,

increased CO2, weed competition, and insect pests, that may lead to a probable decline in crop production. According to their findings, crop yields in Sub-Saharan Africa (SSA) are projected to decline by more than 10% by 2055. This decline was attributed primarily to the increased occurrence of extreme weather events and the interaction of elevated CO2 levels with tempera- ture and rainfall. According to the findings from studies in [4, 7, 25], even though temperature is a significant factor influencing maize production, rainfall and water availability are more restrictive elements. Nevertheless, rising temperatures can make some regions crop yield more vulnerable [7]. An interesting study is the one by Acquah and Kyei [26], who discovered in their paper that, an increase in temperature in Ghana is probably going to make maize output variability worse, whereas an increase in rainfall is probably going to address the problem. A study by Adjei and Kyerematen [27] also found that over the previous five years, rainfall in Ghana’s transitional zone (Nkoranza South Municipality) had significantly decreased, which had a detrimental effect on maize agricultural operations. Even though the study by Atiah et al. PLOS ONE Impact of climate variability on maize yields in Ghana PLOS ONE | https://doi.org/10.1371/journal.pone.0305762 June 25, 2024 2 / 24 Agency and the Statistics, Research, and Information Directorate (SRID) of Ghana’s Ministry of Food and Agriculture) which makes the data confidential. The data can be accessed from these institutions the same manner as the authors

accessed them and that the authors do not have any special privileges in obtaining the data used for these studies. Funding: The first author is grateful for the support from the Kwame Nkrumah University of Science and Technology Research Fund award number KReF 2022/23. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: The authors have declared that no competing interests exist. Abbreviations: CO2, Carbon dioxide; ˚C, Degree Celsius; DT, Decision Tree; GB, Gradient Boosting; KNN, K-Nearest Neighbor; LR, Linear Regression; MAE, Mean Absolute Error; MLP, Multi-Layer Perceptron; mm, millimeters; MSE, Mean Squared Error; mt/ha, Metric tons per hectare; rbf, Radial Basis function; RF, Random Forest; SELM, Stacking Ensemble Learning Model; SSA, Sub- Saharan Africa; SVM, Support Vector Machine; XGB, XGBoost.