Is there an option to plot the Z axis reversed (as shown in the figure)?

Mathematica graphics is interactive. Just drag & rotate the plot with mouse till you flip it up side down. You also can do this programmatically:

Plot3D[Sin[x y]^2, {x, -2, 2}, {y, -2, 2}, ViewPoint -> {-1, -2.5, -1}, 
ViewVertical -> {0, 0, -1}]

Here is how I got these options - if you are curious. Produce Mathematica 3D graphics object and play with it by rotating it around. As soon as you like its orientation excute

Options[%]

And get something like this:

Out[2] = {Axes -> True, BoxRatios -> {1, 1, 0.4},  Method -> 
{"RotationControl" -> "Globe"}, PlotRange -> {{-2, 2}, {-2, 2}, {0., 1.}}, 
PlotRangePadding -> {Scaled[0.02], Scaled[0.02], Scaled[0.02]},  
ViewPoint -> {-1, -2.5, -1}, ViewVertical -> {0, 0, -1}}

Options ViewPoint and ViewVertical will be most important for your particular case. You can use them now in your code to avoid the need to adjust graphics interactively every time.

NOTE (thanks to @Heike comment below):

In some cases if Options[%] does not work you may try this:

which will produce the set of options I showed above.

Using ScalingFunctions

Plot3D[Sin[x y]^2, {x, -2, 2}, {y, -2, 2},
 ScalingFunctions -> {Identity, Identity, "Reverse"}]