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

mean value of 0.39 represents the average carbon dioxide concentration throughout the regions under consideration. Carbon dioxide is a greenhouse gas that contributes significantly to climate change. This mean number indicates that the regions have a given level of carbon dioxide in the atmosphere on average. The coefficient of variation of 35.06% shows the regional variability in carbon dioxide levels. The comparatively high coefficient of variation of 35.06% suggests that carbon dioxide concentrations in Ghana’s various regions vary signifi- cantly over time. Results Trends of maize yield for each region in Ghana In this section, we investigate the variation and trends in maize yield for each region over the period under study in Ghana. Fig 2 clearly show that the yield of maize has increased signifi- cantly across all the regions in Ghana. In Fig 2, the maximum maize yield in all the regions we observed in 2019 except for the Upper East and the Western region which recorded the maxi- mum maize yield in 2003 and 2012 respectively. However, it is observed that it started rising after the year 2015. This increasing trend of maize yield in the regions can be attributed to sev- eral factors which are discussed subsequently. Impact of climate variables on maize yield Although there are numerous climate factors that affect maize output, temperature and precip- itation have the greatest effects on crop productivity [4]. Fig 3 shows how average temperature and precipitation affect maize yield in each region. We fixed the threshold for maximum

maize yield (see Fig 3) at 2.0 mt/ha for all the regions apart from the Northern and Western regions, where the thresholds for maximum maize yield were set at 1.8 mt/ha and 1.5 mt/ha, respectively. This is because the maximum yields of maize in either of these two regions never exceeded 2.0 mt/ha. In the Ashanti region of Ghana, the maize yield is influenced by specific temperature and precipitation conditions. Based on the data presented in Fig 3a, it is observed that higher maize yields are obtained when the average temperature ranges between 27.10˚C and 27.30˚C, and the precipitation amounts fall between 1388.80 mm and 1593.53 mm. The optimal combi- nation is found at an average temperature of 27.15˚C and a precipitation total of 1593.53 mm, which leads to the maximum maize yield. In the Central region as shown in Fig 3d, it is evident that higher maize yields are obtained when the average temperature ranges between 26.60˚C and 27.50˚C, and the precipitation amounts fall between 1217 mm and 1495.00 mm. The opti- mal combination is found at an average temperature of 26.98˚C and a precipitation total of 1489.66 mm, which leads to the maximum maize yield. In the Eastern region as depicted in Fig 3b, the production of higher maize yields is associated with average temperatures between 26.86˚C and 27.61˚C and precipitation amounts ranging from 1168.53 mm to 1615.79 mm. The maximum maize yield occurs at an average temperature of 27.19˚C and a precipitation total of 1615.79 mm. In Volta region as shown in Fig 3c, it is observed that higher maize yields

are obtained when the average temperature ranges between 27.64˚C and 27.76˚C, and the pre- cipitation amounts fall between 1314.30 mm and 1600.11 mm. The optimal combination is found at an average temperature of 27.64˚C and a precipitation total of 1600.11 mm, which leads to the maximum maize yield. In the Brong Ahafo region as shown in Fig 3e, higher maize yields are obtained when average temperatures range from 27.16˚C to 27.81˚C and pre- cipitation amounts fall between 1204.32 mm and 1437.83 mm. The maximum maize yield occurs at an average temperature of 27.53˚C and a precipitation total of 1437.83 mm. In the Greater Accra region (Fig 3f), a maximum maize yield is produced with an average PLOS ONE Impact of climate variability on maize yields in Ghana PLOS ONE | https://doi.org/10.1371/journal.pone.0305762 June 25, 2024 13 / 24