ANALISIS NERACA AIR UNTUK ARAHAN PENGGUNAAN LAHAN OPTIMAL DI SUB DAS GRINDULU KABUPATEN PACITAN

Water demand continues to increase in line with population growth. The increase will be in line with pressure on land use. The need for residential land, agricultural land will continue to urge the catchment area. Dryness are common during the dry season in sub DAS Grindulu will be a threat that can�t be avoided if land use in fulfilling these needs are not done wisely. This study was aimed to determine the condition of the water balance, aridity index, and simulate the optimal form of land use to increase the availability of water in sub DAS Grindulu. The research method used is the method of Thornthwaite Mather. Sub watershed areas are divided into five regions and water balance calculation is performed to obtain information of water deficit (D), water surplus (S), and aridity index (Ia) of each region. Simulation of land use changes made by the willingness of the community. The simulated land area obtained from the percentage of people who are willing to change the landuse. Directions of the proposed changes adjusted with the wishes of the people by considering the direction of area function. The results showed the condition of the water balance in the fifth regions in sub DAS Grindulu are varied. The largest water deficit was at region III of 467.7 mm/ year (May to October) and the lowest was at region I of 249.46 mm/ year (June to September). The largest surplus water was at region V of 967.39 mm/ year (October to May) and the lowest was at region III a of 384.93 mm/ year (November to April). The Aridity Index in sub DAS Grindulu are mostly in the criteria of medium water shortage (region I- IV). Aridity index sequence of region I, is 18.21%, 17.74%, 22.09%, 21.48%, 12.74%. The effect of landuse are significantly affected the result of a regional water supply. Simulation of land use change managed agroforestry systems in each region showed positive results. Water deficit in the region III before the simulation is the largest deficit, it may drop to 440.11 mm/ year after simulated. Aridity index also changed after the simulation, as in region IV can achieve index decreased by 4.51% from the previous