Validation of the weather generator CLIGEN with daily precipitation data from the Loess Plateau, China

SummaryWeather generators are widely used in hydrological, ecological, and crop-yield modeling. CLIGEN is a frequently adopted weather generator. Although it has been tested in many parts of the world, it still needs to be validated before being applied to the Loess Plateau, China, because of the unique climate of the region. Only the generated daily precipitation are validated in this paper, for it is assumed to be the most important climatic factor affecting the precision of SWAT, which was selected as the main tool to do a regional assessment of soil erosion. Five sites, which have 30 years of relatively complete daily precipitation records along an aridity gradient, are selected for the validation of CLIGEN. The main purposes of this study are to test the usefulness of CLIGEN in precipitation simulation and to determine whether the performance varies with the aridity gradient. Means and standard deviations of five rainfall variables between measured and each of the 10 sets of CLIGEN generated precipitation are compared for each site. The precipitation variables analyzed are: yearly total precipitation, yearly number of rainy days, monthly total precipitation, log-transformed monthly average wet-spell length, and log-transformed monthly average dry-spell length. T-tests and F-tests are used to determine if there are significant differences in the means and standard deviations, respectively, between observed data and CLIGEN-generated data. Results show that CLIGEN preserves the means quite well, and preserves standard deviations reasonably well, although there are considerable variations among sites, among precipitation variables, and among seasons. There is no obvious trend of performance along the aridity gradient.