A Geospatial Big Data Approach for Web Mapping of Water Balance & Dry Days in Indonesia's Peatlands

Peatlands in Indonesia, covering approximately 24.67 million hectares by the end of 2015, are predominantly found in the provinces of Riau and West Kalimantan. These ecosystems are critically dependent on the interplay between vegetation, water, and peat, making effective water management essential for their restoration and conservation. Accurate identification of water surplus and deficit periods is crucial for devising appropriate management strategies. This study investigates the water balance and consecutive dry days in two Peatland Hydrological Units (PHUs): Tebing Tinggi Island and Mempawah River-Peniti River. Utilizing the Geospatial Big Data platform Google Earth Engine (GEE), and employing TerraClimate data for monthly water balance and CHIRPS data for dry day analysis, the study spans the period from 2010 to 2020. Calculations of precipitation, evapotranspiration, and runoff were performed, and the results are visualized in two interactive web maps via the GEE App. Findings reveal that Tebing Tinggi Island experiences water deficits during February-March and June-July, while Mempawah River-Peniti River displays a more irregular pattern. Sub-PHU 2 on Tebing Tinggi Island and Sub-PHU 6 on Mempawah River-Peniti River are identified as the driest areas. The usability of the interactive water balance map was assessed through a questionnaire, achieving a Likert scale index of 86.75%. A Pearson correlation test indicated a positive relationship between water storage changes and the Normalized Difference Water Index (NDWI), with correlation coefficients of 0.69 and 0.74 for Tebing Tinggi Island and Mempawah River-Peniti River, respectively.