Climatic Water Balance and Agricultural Production in the Northern Plains of West Java

Abstract

Indonesia is an agricultural country which at present is concentrating much of its development funds and efforts on improving agricultural production, especially rice, to meet the growing demands for food and job opportunities for a rapidly expanding population. Irregular rainfall and inefficient management of the available water resources result in damage to rice plants and production. Good water management, i.e., the control of water for the most efficient use of limited supplies to obtain optimum crop yield, is needed. The problem of optimum water distribution can be solved only when various water balance components and the response of crops to water application are understood. The purpose of this study is to determine the water balance of the Northern Plains of West Java, to analyze its components under the influences of local meteorological factors, and to relate water balance conditions to agricultural production. Several empirical methods to estimate potential evapotranspiration have been tested to determine which is best suited to tropical conditions. A linear regression analysis has been performed in order to measure the relationship between global radiation and sunshine duration (Q/QA = a + b n/N) for Jakarta during the period 1964-1971. The predictive formula which was derived is Q/QA = 0.19 + 0.38 n/N, with a standard error of 0.09 and a correlation coefficient of 0.69. Potential evapotranspiration isolines and water balance diagrams for eight stations, Serang, Jakarta, Depok, Subang, Jatiwangi, Kadipaten, Cirebon and Tersanabaru are presented. A close correspondence has been found between poor rice harvests and periods of severe water deficits in West Java during the period 1955-1975.