By introducing levy-lindeberg theorem to raingauge networks planning, the authors obtain a linear relationship between the measurement precision of areal rainfall (relative error or permissible error) and raingauge networks density (average station spacing). The slope of relative error growing is directly proportional to the mean square error of random observation error, inversely proportional to square root of the areal rainfall and region area. Based on simulated rainfall fields and highdensity rainfall data during Mei-yu season in Anhui Province, conclusion above is validated by the statistic analysis reducing the raingauge stations method. The slope of the linear relationship is also investigated. This research is significant to provide certain reference for optimization of raingauge networks location planning. Based on the relationship, the authors calculate 2005-2008 rainfall data during Mei-yu season in Anhui Province and conclude that correlation coefficient between the measurement precision of areal rainfall and raingauge networks density in Huaibei Plain is 0.49 to 0.80, in the mountains of Southern Anhui Province is 0.70 to 1.41. Assuming that permissible error is 20%, the minimum average station spacing (the maximum Raingauge networks density) in Huaibei Plain is 25 km and in the mountains of Southern Anhui Province is 14 km.

The three-dimensional water vapor field is obtained using Monte Carlo tomography algorithm based on the small-scale network of ground-based GPS. After the proof of the accuracy of the tomography water vapor field through the comparison between the profiles from the radiosonde and tomography field, the three-dimensional water vapor field and the data of Weather Radar are used to study the variation of the water vapor in the strong convection and heavy precipitation processes which took place on July 29, 2011. For the first time, the authors propose the continuous change and fine structure of the small-scale water vapor field during the convective processes. For local convection process, the tomography vapor field can capture the water vapor enrichment phenomenon and provide its location 20 minutes ahead the precipitation and it is an indication to the precipitation forecast. For rainstorm process, the water vapor field can explicitly show the position and intensity of the vapor transport source which meet well with the conclusion from the analysis of weather radar and meteorological situation.