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

本数据集收录了美国地质调查局国家水资源信息系统（https://nwis.waterdata.usgs.gov/usa/nwis/peak; accessed 10 June 2021）中CAMELS流域的峰值流量观测数据。研究团队对每个CAMELS流域所有可用的年度峰值流量进行了分析，并采用矩估计法将数据拟合至Pearson Type III分布，经对数变换后，具体概率密度函数表达式为：f(x| au, alpha, eta) = frac{(frac{x- au}{eta})^{alpha-1}exp(-frac{x- au}{eta})}{|eta|gamma(alpha)}。在洪水流量未因水库调控、流域变化或异常事件（如大坝故障）而显著改变的前提下，CAMELS流域适用于此方法。研究团队利用Mathworks File Exchange提供的Matlab代码，将峰值年流量事件拟合至分布，以获得每个流域的回归周期估计值（Burkey, 2009）。这些回归周期计算亦可通过美国地质调查局提供的免费开源软件（https://water.usgs.gov/software/PeakFQ/; accessed 10 June 2021）完成。根据每个流域观测到的峰值年径流量的回归周期，将各流域的水文年份（流域-年份）进行了分类。