*3.1. General Approach*

A main result of this study is the general approach developed, used and tested for robustly assessing freshwater changes in terms of catchment-scale long-term average *ET* and *R*, driven by climate and landscape (here irrigation) developments from an earlier period (here 1930–1949) to recent conditions (here 1990–2009). Figure 4 illustrates schematically this principal approach, which is based on fundamental catchment water balance, aiming to constrain the result and uncertainty ranges of different possible variable evaluations. This approach provides a consistent flow-chart basis for corresponding quantitative assessments of freshwater changes in various comparative scenarios and catchment cases. Different scenarios may represent various possible variable evaluations from limited available observation data and the catchments may be of different scales and in different parts of the world.

**Figure 4.** Schematic illustration of the approach developed and used to assess long-term average evapotranspiration (*ET1*) and runoff (*R1*) in an early 20-year period and associated changes (Δ) from this to a recent 20-year period. The sources and types of data used for the assessment in this study are exemplified for the base case scenario in the light blue boxes to the left, grouped as: atmospheric climate, landscape water and irrigation data. The variables extracted from the data are shown in the dark blue boxes. The green boxes show intermediate derived variables for estimating the different components of total *ET* change, as outlined in the red boxes and synthesized in the yellow box. The lilac box shows the final synthesis for estimating corresponding components and total change for *R*.

**Table 3.** The base case and alternative (Alt.) evaluation scenarios and their variations. Results are listed for the total regional catchment, with the terms *P*, *ET*, *Iww*, *αirr* and *Per* representing precipitation, evapotranspiration, irrigation water withdrawal per irrigated area, ratio *Aai1*/*Aai2* between irrigated area (*Aai*) and time period. The latter is period 1 (1930–1949) or period 2 (1990–2009).

