Water balance changes in the tropical rainforest with intensive forest management system

Abstract

Understanding the water balance changes in the forested area is important for managing the sustainability of water resources and anticipating potential disturbance caused by the implementation of a particular forest management system. This study was conducted in a natural tropical rainforest of Central Kalimantan, Indonesia. The objective of this study is to determine the water balance changes in the tropical rainforest under Intensive Forest Management System (IFMS) using a Thornthwaite Mather Water Balance (TMWB) model. The TMWB model calculates the water balance based on long-term average monthly precipitation, potential evapotranspiration, and combined latitudes, soil properties, and vegetation characteristics. The results found a good agreement between the predicted and observed monthly streamflows both in the natural forest and treated forest. In the natural forest found the runoff coefficient is 0.5. It is assumed that 50% of the surplus water is actually available as streamflow in any given month, and the rest become detention water to supply soil moisture and ground water. It is also assumed that 50% of detention water is available as streamflow in the next month. 1-year after IFMS treatment, the runoff coefficient increased to 0.6. Canopy cover reduction in the treated forest has reduced the annual evapotranspiration approximately in 45.3%, while the annual runoff has increased approximately in 33.7% from natural forest. The overall results of calculations using the the TMWB method indicated that the water balance status and runoff are not experiencing the problems leading to water deficit under natural tropical forest conditions. These results suggest that in the forested area, a strong relationship exists among rainfall, evapotranspiration, and runoff production. Surface disturbances, land-use changes, and reductions in canopy cover potentially impact the water balance—in particular, they influence evapotranspiration and infiltration processes that reduce evapotranspiration and increase runoff.