Evaluation of Seasonal Cycles of Hydrological Processes in Japan Meteorological Agency Land Data Analysis

The present study evaluates the reproducibility of the climatological seasonal cycles of three hydrological variables, soil moisture, river discharge and terrestrial water storage in the Japan Meteorological Agency Land Data Analysis (LDA) by means of a system consisting of the LDA and a global river-routing model (LDAG). LDAG satisfactorily reproduces the seasonal cycle of soil moisture at most of the observation stations; however, negative correlations are found at stations in the mid latitudes of east Eurasia. The amplitudes of river discharge are well reproduced only in a few rivers. The relative errors of the amplitudes exceed 20% in many of the rivers. The correlation coefficients of the seasonal cycle are more than 0.5 in most of the 70 rivers investigated. The phase differences occur within one month in most of the rivers. The relative errors of the amplitude of terrestrial water storage are less than 10% in five of the top 10 largest river basins, and the correlations are high at the river basins located in areas such as the tropics and the Asian Monsoon region. The LDAG phases are generally earlier, similar to those of river discharge. Close examinations demonstrate that better reproducibility requires improvements in both the numerical model and the forcing data. Despite good reproducibility only in some river basins, the hydrological variables produced by LDAG may be useful for land surface initial conditions for weather forecasts and hydrological studies.