THE EFFECT OF TREE CANOPY STRUCTURE ON SPATIAL RAINFALL REDISTRIBUTION DURING POST-ERUPTION RECOVERY OF MOUNT MERAPI, JAVA ISLAND

The tree canopy around Merapi Volcano, Yogyakarta, Indonesia, has a unique structure. The frequency of volcanic eruptions influences the uniqueness of the structure, as it is a response to volcanic ash and rainfall characteristics. This research was conducted on eight species that have different canopy structures. In contrast to the trees canopy that was not affected by eruptions, the tree canopy around the Volcano has more dynamic canopy surface characteristics during the recovery period. The redistribution of rainfall in the tree canopy was traced by calculating unit area discharge and droplets' probability in each canopy structure segment. The results of empirical throughfall calculation and throughfall direct observation were tested using ANOVA. Most of the throughfall occurs simultaneously under the canopy during rain with a depth of 3.5 - 72.5 mm or intensity of 10 - 20 mm/hour (observed = 58% and empirical = 57%). The existing range of rainfall intensity or rainfall depth shows that the process of redistribution of rainfall in the canopy has time constraints and canopy storage capacity constrain. The canopy surface characteristics have a more significant effect than the canopy structure on the redistribution of rainfall. The canopy surface serves as a sheet of rainfall concentration to the next section. The important canopy surface structure parameters to rainfall concentration are leaves characteristics, branches stiffness, and crown density. Knowledge of the tree canopy's rainfall flow distribution process will help manage conservation-based rehabilitation activities in areas prone to volcanic disasters.