Figure 10: Yearly sum of precipitation during the main irrigation season (May-Oct), irrigation, and harvest averaged over all apple orchards within the PHO from 2016 to 2022, under full irrigation (FI) and the difference for the 75 % and the 50 % deficit irrigation scenarios (DI75 and DI50).
Figure 11 shows the seasonal course of irrigation, precipitation, and fruit growth in the apple orchards averaged over the PHO and the 7-year period. The simulated irrigation season starts in April or May and lasts until October with negligible amounts still applied in November for some years. Monthly irrigation requirements increase sharply between April and June until reaching their peak in August with on average 107 mm per month. Accordingly, August is also the month in which the greatest water savings occur for the deficit scenarios. After that, irrigation declines rapidly. Fruit biomass increases steadily from April to harvest in September with faster growth occurring in the earlier months. While fruit growth is barely affected by a 25 % reduction in irrigation (DI75), for the DI50 scenario it decreases sharply in August and to a smaller extent in July and September. The reduced fruit growth results in a yield loss of on average 0.5 t ha-1 for DI75 and 6.5 t ha-1 for DI50.