SiBUC (Simple Biosphere including Urban Canopy) is one of the participants of the Second Global Soil Wetness Project (GSWP2). It uses mosaic approach to incorporate all kind of land-use into LSS. Precise description of cropland is one of the important aspects of SiBUC. Paddy field scheme is newly developed to treat the rice paddy field, which has water layer above the soil surface, differently from other cropland (farmland). As for farmland, 5 types of crops are considered; spring wheat, winter wheat, corn, soybean, and cotton.

Although not a small part of the world's cropland is irrigated (Siebert, S. et al., 2002), the baseline simulation of GSWP2 pays no attention to this effect. In order to estimate global soil moisture field as realistically as possible, SiBUC is run with irrigation scheme activated. Basic concept of the irrigation scheme is to maintain the soil moisture (water depth) within appropriate ranges that are defined for each growing stage of each crop type.

The main tasks for the implementation of irrigation simulation in global scale are to prepare a global dataset of crop type and cropping calendar with 1-degree resolution. Paddy field area is separated from cropland area based on the Olson Global Ecosystem dataset. Through the time series analysis of NDVI, farmland is classified into 5 types and global distribution of cropping calendar (seeding, harvesting, etc.) is produced.