camels peak annual flow and return period

Peak flow observations for each of the CAMELS basins from the USGS National Water Information System (https://nwis.waterdata.usgs.gov/usa/nwis/peak; accessed 10 June 2021).

We used all available annual peak flows for each of the CAMELS basins and fit these values to the Pearson Type III distribution with log transformation using the method of moments, as described in U.S. Interagency Committee on Water Data,Bulletin 17b (IACWD, 1982). The probability density function is: f(x|\tau, \alpha, \beta) = \frac{(\frac{x-\tau}{\beta})^{\alpha-1}exp(-\frac{x-\tau}{\beta})}{|\beta|\gamma(\alpha)}, The CAMELS basins are suitable for this method under the assumptions of flood flows that are not appreciably altered by reservoir regulation, watershed changes or where the possibility of unusual events, such as dam failures.

We used Matlab code from Mathworks File Exchange to fit the peak annual flow events to the distribution to obtain return period estimates for each basin (Burkey, 2009). These return period calculations can also be done with free and open source software available from the USGS (https://water.usgs.gov/software/PeakFQ/; accessed 10 June 2021). We classified the water year of each basin (basin-year) according to the return period of its observed peak annual discharge