The first graph is for rainfall versus inflow for the last 14 years (23 years worth of data). As you can see, the R^2 value is .93, which is a very good fit.
The second graph is for rainfall decline over time for the same period. Again, there is a very good fit.
I have extended the graphs forward so that the conclusions of the previous post can be seen. By 2017, rainfall will drop below 450 mm. By that point, runoff will effectively be zero.