Abstract

The water balance analysis reveals the percentages of precipitation made up by surface flow, evapotranspiration, groundwater recharge and the change of soil storage, all of which are considered useful to the further understanding of the hydrological processes. Growing periods can be determined using water balance analysis to decrease harvest risk in certain area. The experiment objective was to determine growing periods of food crop in at Penajam Paser Utara district. Modified method of Thornthwaite and Mather of bookkeeping system of water balance was used based on monthly data. Rainfall and another parameter of climate data were collected from 21 Meteorology stations, then to be analyzed in order to determine land water balance. Monthly land water balance indicated that Penajam Paser Utara area, there were 7 months water surplus (January to June, and December), it was 613 mm/year, while water deficit occurred during 4 months (July to October), it was 22, 4 mm/ year. Optimally, at Penajam Paser Utara area, there was 11 months period for twice rice planting, and once for other food crops.