code: private double svp_slope( double temp ) {
          double satVaporPressureSlope = (B_SVP * C_SVP) / ((C_SVP + temp) * (C_SVP + temp)) * svp(temp);
  
          return satVaporPressureSlope;
      }
docs: This routine computes the gradient of d(svp)/dT using Handbook of Hydrology eqn 4.2.3
  @param tair
  @return saturated vapor pressure slope