ENSO events impacts on apple production in Shandong Ⅰ: A study of changes in apple climatic resources and yields under different scenarios

El Niño-Southern Oscillation (ENSO) is one of the strongest ocean-air coupling systems in the world. Furthermore, ENSO events have a major impact on climate resources and agriculture in China. Shandong is one of the major apple-producing areas in China. The variation in apple yield is affected by local climate conditions, cultivated varieties, and management. Analyzing the influence of climate change on local apple yield under the influence of ENSO events is of great significance. Therefore, based on the daily meteorological observation data, county-level apple planting statistical data in Shandong Province, and worldwide ENSO data from 1991 to 2019, the spatio-temporal variation in climate resources in the apple growing period in Shandong Province under different ENSO types were analyzed, and the impact of climate resources on local apple yield was explored. The results showed that: 1) the apple planting area in Shandong Province first increased and then decreased, while the total yield and yield per unit area increased significantly from 1991 to 2019. The center of gravity of the apple planting area and total output moved from Weifang to the Jiaodong Peninsula, while the center of gravity of the yield per unit area moved from the center to the southwest in Weifang. 2) There was no significant correlation between the climate resources and ENSO events in different ENSO years. The spatial distribution of the apple growing period climate resources was not uniform for different ENSO years. The light resources decreased from north to south, while the heat resources increased from east to west. The precipitation decreased from south to north. Light and heat resources were superior in El Niño years, and precipitation resources were superior in La Niña years and neutral years. 3) There was a negative relationship between the climatic resources and meteorological yield per unit area in different ENSO years, which restricted the apple meteorological yield per unit area to some extent. The precipitation resources in El Niño and La Niña years were positively correlated with the apple meteorological yield per unit area, while the precipitation resources in neutral years were negatively correlated with the apple meteorological yield per unit area. Superior climatic resources have a positive effect on apple production. Excessive climatic resources can cause a certain degree of inhibition of apple yield. In the future, it is necessary to focus on high temperature, drought, and other related disasters during El Niño years, low temperature and flood disasters in La Niña years and neutral years to avoid the impact of meteorological disasters and ensure the healthy development of the local apple industry.