Reanalysis of Global Soil Wetness and its Application to Numerical Rainfall Forecasting

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Global climate system, atmosphere and rainfall patterns have been know as to be critically much influenced by the underlying boundary conditions such as sea surface temperature (SST), soil moisture, snow and so on. In particular, the effects of soil moisture and its anomaly have been a matter of intensively investigated in these several years. The Global Soil Wetness Project which was carried out a few years ago provided a comprehensive dataset of soil moisture in 1987 and 1988 with the utilization of land surface models for global climate models or global hydrological models. However, there still remains possibility to improve this dataset and to utilize the dataset for the impact study whether rainfall forecasting is much affected by soil moisture or not.As a consequence of this research in two years, at first, an international proposal called Global Soil Wetness Project 1.5 is presented in the international community of global hydro-climatology. For it, a correction method is propos … More ed to improve precipitation amount in the northern (colder) part of the globe in winter. The new dataset with the improvement is constructed and can be open through internet.Secondary, the effects of soil moisture on rainfall simulation with a climate model were investigated.Three sets of soil moisture, the product of Global Soil Wetness Project, satellite derived soil moisture with remote sensing, satellite-based soil moisture but modified through the relationship found in Global Soil Wetness Project analysis, were applied to the seasonal rainfall forecasting with a climate model especially focusing on climate in the tropics. Results indicated that the modified method based on Global Soil Wetness Project analysis has great potential to utilized remotely sensed surface soil moisture for rainfall forecasting. However, basically, the impacts of soil moisture may not be so strong compared to sea surface temperature especially in the tropics. Further investigation and trial are indispensable.At last, considering that global soil wetness and runoff calculated in the sequence of global soil wetness project must be water resources in the world itself, global water resources assessment was conducted with the products of the project. In addition to the natural water resources derived from the products of the project, amounts of water withdrawal by human beings were compiled with several statistical and GIS-based datasets. A current estimates of water scarcity in the world at 0.5 degree basis was obtained through it. This framework can be utilized for possible assessment of expected future water scarcity. Less