Figure 6.10.2 Distributional changes in PED at the Lincoln (left) and Napier (right) gridpoints, comparing historical distributions with those projected by Hadley model with IPCC 75%ile scaling

Text description of figure

The figure consists of two line graphs, each with three curves, showing the PED probability density function versus PED value: the left graph applies to Lincoln, and right to Napier. Each graph contains the distribution curve for historical data, and for the Hadley model with 75% scaling in the 2030s and the 2080s. The Lincoln historical distribution shows a broad peak near 0.2 for a PED between about 200mm and 650mm. In fact, there is an indication of bimodality in the data, with frequency of occurrence peaking near 250mm and 600mm. The two curves for the future scenarios are shifted to higher PED values, and are somewhat broader (and therefore have smaller vertical extent). The 2080s Hadley scenario has the lowest peak probability density (about 0.16-0.17) and largest shift to higher PED values (ranging from 350mm to 900mm). The sequence of curves implies an increase in PED in future climates.

The three curves for the Napier site show a similar behaviour as at the Lincoln site, indicating conditions progressively drier with time. The difference is that the Napier curves are more sharply peaked and clearly unimodal. The historical data peaks at a PDF of nearly 0.25 for a PED value of about 400-450mm, the Hadley 2030s curve peaks at a PDF of around 0.23 for a PED value of 550-600mm and the Hadley 2080s curve peaks at a PDF of 0.21 at 650-700mm. For both sites, the historical PDF has dropped to zero by about 1000mm PED on historical data, and about 1250mm PED on 2080s scenario data, with the 2030s being an intermediate case.