Figure 7: Seasonal mean soil moisture, and evapotranspiration sums in the PHO catchment, averaged over the period 2016-2022.

3.2.2 Simulated spatial patterns

Figure 8 shows average and standard deviation of the 7-year simulation period for irrigation, SM, yield, and CWUE for all apple orchards in the PHO, between 2016 and 2022. Modeling results show a clear spatial pattern that is driven by climatic conditions following the topographic gradient (Figure 1) on the one hand and soil characteristics on the other hand (Figure 2). Average yearly irrigation requirements range between 400 and 450 mm in the plain. The highest values are found in the southeast while considerably lower values occur at higher altitudes in the northern part of the catchment (<200 mm). Harvest values show a similar pattern because cooler temperatures and lower incoming radiation in the northern part of the catchment result in lower crop productivity and thus smaller yields (16-38 t ha-1) compared to the plain where yields are around 50 t ha-1 without much spatial variability. In addition to lower crop productivity and thus lower crop water demands, spatial variability in irrigation requirements results from the higher precipitation in the upper parts of the catchment that further reduces the need for irrigation as well as soil textural differences. The latter is most evident in the southern part of the catchment where the higher clay content and the consequently higher water holding capacity of the soil result in increased evaporation (not shown). This in turn generates a greater irrigation demand resulting in slightly lower CWUE of orchards planted on these soils. Soil textural differences are also reflected in the SM plot where areas with a higher percentage of clay or organic matter show higher SM values than areas with sandier soils or soils that are lower in organic matter. CWUE ranges from 57-65 kg ha-1 mm-1 in the plain to 35-45 kg ha-1 mm-1 in the northern part of the catchment and largely reflects the spatial patterns of irrigation and harvest whereby high irrigation requirements and low harvest lead to low CWUE. Inter-annual variability (standard deviation plots) within the catchment shows similar patterns for irrigation, harvest, and CWUE and is higher in the northwestern part of the catchment. The higher variability was driven by local temperature differences in some years that delayed the onset of the growing season up to 14 days compared to the remaining orchards. Inter-annual variability of SM is generally low without a distinct spatial pattern.