ザンベジ川氾濫原の水収支と水田の純用水量の推定

Abstract

The analysis of the meteorological data and soil moisture observed in the cool-dry season at the Zambezi river flood plain and Mongu meteorological station shows that water supply from groundwater covers almost two-third of the actual evapotranspiration rate in the objective development area and amounted to 1mm/d.The potential evapotranspiration rates in this area after the development as paddy field were estimated at more than 6mm/d for hot-dry season. These rates can be considered as a proper rate, because in this area there is a lot of fair or partly cloudy days with low humidity in hot-dry season. It was found that net radiation had direct effect upon the evapotranspiration rate. So if it is needed to get more accurate rate for paddy field, the estimation of net radiation based on the albedo, changed the value for soil surface conditions as growing stage of paddy rice, would be more important.Estimated from the water budget and the potential evapotranspiration rate as paddy field in this area, daily rates of the net water requirement for the year 1994 were ranged between 6mm/d and 14.5mm/d, and indicated larger rates in the dry season from April to October than in the wet season from November to March.In this study, the percolation loss was estimated in the verification paddy field from the water budget equation. At place where all terms of the water budget are not available, the value of percolation loss should be carefully decided based on the water supply from groundwater.