The impact of land use and land cover change on hydrological processes in Brantas watershed, East Java']Java, Indonesia

Assessing the impact of land use and land cover change (LULCC) on hydrology is essential for water resource management. The Brantas watershed contributes about 30% of the water supply of the East Java region. The present rapid pace of land occupation for agriculture and settlements is expected to continue to alter flow processes within the watershed. This study aims to simulate LULCC and its impact on the hydrological processes of the watershed. The long-term impact of LULCC is evaluated using the Soil and Water Assessment Tool (SWAT). The analysis model is calibrated using monthly data series from 1996 to 2005 and then validated using data series from 2006 to 2015. Two editions of maps (2001 and 2015) are then used to calculate the LULCC that took place across this period. The impacts of LULCC on hydrological processes at the sub-basin level are also evaluated. The results show that the variability of rainfall patterns from 2001 to 2015 strongly affected flow variability. The LULCC from agricultural land to other uses (irrigated rice fields, settlements, and forests/plantations) is most evident in three sub-basins (sub-basins 2, 9, and 17). However, each sub-basin may respond differently with respect to the LULCC taking place. The increase in the area occupied by each class of land use and cover use (LULC) is not always linear to the observed flow, and widely differing LULC classes may display similar flow responses while classes with similar characteristics may have differing impacts on flows within a sub-basin. In other words, the hydrological processes are too complex to be simplified at the sub basin level.