Going From ϕ (Temperature) to velocity/vectors

ClearAll["Global`*"]
size = 10.0;
Temp[x_,y_]=2 x y - (x^2) +5y;
vx[x_,y_]=-D[Temp[x,y],x] ;
vy[x_,y_]=-D[Temp[x,y],y];

plot1=ContourPlot[Temp[x,y],{x,0,size},{y,0,size},Contours->10,ColorFunction->Function[{x,y},Hue[((.95-x)*0.75)]]];
plot2=VectorPlot[{vx[x,y],vy[x,y]},{x,0,size},{y,0,size},VectorStyle->{Thick,Black},VectorScale->{Automatic,Automatic,Automatic},VectorPoints->Coarse,VectorColorFunction->None,VectorStyle->Black];

Show[plot1,plot2]