The only word I can think of is nonsmooth.
Can anyone suggest some other words?
In a mathematical or scientific way, you can describe it as, "initially decreasing, and then increasing in a linear path until it reaches a peak and begins to drop".
Or, if you want to describe a surface like that, you can say "jagged", "rugged", "uneven", and "spiky".
From a scientific point of view I'm not sure what the curve is or what it is really trying to show.
I'm assuming that there is some sort of signal and some sort of noise. Typically if I had an experiment where I collected some data which I plotted, without manipulation, I'd call that a plot of the "raw data." I might say something like "as can be seen the signal is quite noisy."
There are various ways to manipulate the data to "smooth" the curve which tends to improve the S/N ratio. So there is another connotation of "smooth."
Mathematically there is also the notion of a "smooth curve" which has implications of its own.
You could call that a rough curve
rough (adj.) having an uneven or irregular surface; not smooth or level.
(Oxford Living Dictionary)