USGS HYDRO-CLIMATIC DATA NETWORK (HCDN): MONTHLY CLIMATE DATABASE, 1951-1990

Time series of monthly minimum and maximum temperature, precipitation and potential evapotranspiration were derived for 1337 watersheds in the conterminous United States for sites found in the national streamflow database, termed the hydroclimatologic data network (HCDN), developed by Slack et al. (1993a,b). Estimates were derived for the years 1951-1990.This HCDN data set consists of records of average daily streamflow at 1553 sites located throughout the United States. The data meet certain measurement accuracy criterion outlined by Slack et al. (1993). The HCDN contains river flows from 1874 to 1988, with an average record length of 44 years. The streamflow data included in the HCDN is purported to be relatively free from anthropogenic influences and the accuracy ratings of these records are at least rated good per USGS standards. A subset of the HCDN streamflow sites from 1337 watersheds with at least 10 years of record length was used. This subset includes 1376 HCDN sites.The climate characteristic estimates of temperature and precipitation were estimated using the PRISM (Daly et al. 1994, 1997) climate analysis system as described in Vogel, et al. 1999.Estimates of monthly potential evaporation were obtained using a method introduced by Hargreaves and Samani (1982) which is based on monthly time series of average minimum and maximum temperature data along with extraterrestrial solar radiation. Extraterrestrial solar radiation was estimated for each HCDN basin by computing the solar radiation over 0.1 degree grids using the method introduced by Duffie and Beckman (1980) and then summing those estimates for each river basin. This process is described in Sankarasubramanian, Vogel, and Limbrunner, 2001.The data files are organized in directories by parameter, Tmax, Tmin, Pre, and PET, and contain 18 subdirectories representing the 18 HCDN regions. Each region subdirectory contains data files for the monthly time series of respective hydroclimate attributes (Tmax, Tmin, Precipitation, and PET) for the individual HCDN sites in that region for the years 1951-1990. All files are in space delimited ASCII format.

针对美国本土1337个流域，基于美国国家径流数据库中收录的站点，推导得到了逐月最低气温、最高气温、降水量及潜在蒸散发的时间序列；该数据库由Slack等人（1993a、1993b）开发，被命名为水文气候数据网络（hydroclimatologic data network, HCDN）。相关估算的时间跨度为1951年至1990年。该HCDN数据集包含全美1553个站点的逐日平均径流记录，这些数据符合Slack等人（1993）提出的测量精度标准。HCDN收录的径流数据时间跨度为1874年至1988年，平均记录时长为44年。HCDN收录的径流数据据称基本不受人为活动影响，且按照美国地质调查局（United States Geological Survey, USGS）的标准，这些记录的精度评级至少为“良好”。本研究选取了来自1337个流域的HCDN径流站点子集作为研究样本，这些站点的记录时长至少为10年，该子集共包含1376个HCDN站点。气温与降水的气候特征估算采用了PRISM气候分析系统（Daly等人，1994、1997），具体实现方式详见Vogel等人1999年的研究。逐月潜在蒸散发量的估算采用了Hargreaves与Samani（1982）提出的方法，该方法基于逐日平均最低气温、最高气温的月时间序列，结合地外太阳辐射数据完成计算。针对每个HCDN流域的地外太阳辐射估算，首先采用Duffie与Beckman（1980）提出的方法，计算0.1度网格下的太阳辐射，再将各网格的辐射估算值按流域求和；该计算流程详见Sankarasubramanian、Vogel及Limbrunner 2001年的研究。数据文件按参数类型分为Tmax、Tmin、Pre及PET四类目录，并包含18个子目录，分别对应18个HCDN区域。每个区域子目录内包含对应区域内所有HCDN站点在1951年至1990年期间的各水文气候要素（Tmax、Tmin、降水量、PET）的月时间序列数据文件。所有文件均采用空格分隔的ASCII格式存储。