As described in this paper, we attempted real-time rainfall detection by analyzing the radiowave fluctuation of leaky coaxial cables (LCX), which are widely used in Japan as communications antennas. Because the radiowavefluctuation of communications antennas caused by rainfall is extremely slight and contaminated by noise, it is almost impossible to detect rainfall directly from that fluctuation. However, we specifically examined discontinuous changes of the signals caused by water droplets adhering to the antenna surface. Then we tried to evaluate the discontinuous characteristics at each signal point by a singularity, which is mathematical index. Using wavelet transform, we estimated the singularities of signal fluctuation measured outdoors. Comparison of the 1-min average of the singularities with the 1-min rainfall intensity revealed a difference in singularities between those occurring with rainfall and without rainfall. Statistical analysis revealed a time variation of singularities using Boxplot method. Results show a significant difference in the singularities of the signals obtained during rainfall to the distribution of the signals during no rainfall. Therefore, it might be possible to detect rainfall in real time by ascertaining differences in the singularities of the radiowave fluctuation of LCX.

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 To improve simulation accuracy of river discharge and to quantify the hydrological cycle in irrigation-dominant basins, we developed a reservoir operation model and a water allocation and management model, and combined them to a water circulation model incorporating paddy irrigation schemes. Paddy field irrigation uses large amounts of water in monsoon Asia. River flow regulation through impoundments and diversions with large reservoirs strongly influences water circulation in river basins. Therefore, considering various water management processes for reservoirs, diversion weirs, irrigation canals, and paddy plots is crucially important for accurate estimation of river flows and for elucidation of regional hydrological cycles. To verify the simulation accuracies of water management processes and river discharges, we applied the developed model to the Mun River Basin in northeastern Thailand, which has many irrigation projects. Results revealed the following: 1) The water allocation and management model precisely represents seasonal fluctuations in the amount of water withdrawals at diversion weirs and at paddies, which depend on paddy water requirements. 2) The reservoir operation model reproduces water management during the rainy seasons and the release of irrigation water in response to water requirements during dry seasons. 3) Modeling of water management in reservoir irrigation improves the simulation accuracy of river discharge in dry seasons when the water release from reservoirs is dominant in river flows.

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 This study investigated the melting layer detected by X band polarimetric radar (XMP). The feature of melting layer provides important information for quantitative precipitation estimation. XMP was used to observe upper areas for detecting initial symptoms of precipitation every 5 min. A 20-degree elevation was used for investigating melting hydrometeors. The analysis period was October 2010 – October 2011. Days when the daily rain amount was more than 10 mm were objects for study as analysis days. The melting layer existence was investigated at observation times(every 5 min) when the radar reflectivity index was higher than 25 dBZ near the surface on the analysis day. The polarimetric melting layer (PML), which was defined by the minimum of co-polar correlation coefficient (ρ_HV), was located lower than the reflectivity melting layer (RML), which was defined by the maximum of the radar reflectivity index, known as brightband. Furthermore, the PML width was less than that of RML. The different height or width between PML and RML was regarded as a reflection of the rain size distribution. Improvement of the rainfall estimation method was attempted by optimizing the coefficients in ZR relation according to the difference between the height of PML and that of RML. Rainfall estimations using variable coefficients were better than those using fixed coefficients.

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