Hydroclimatic Drivers of Dissolved Organic Carbon in Asia's Major Rivers

Abstract

Dissolved organic carbon (DOC) plays a vital role in the global carbon cycle, with river discharge as a major transport mechanism from land to ocean. As the second-largest freshwater contributor to oceans, Asia experiences significant hydroclimatic variations, yet, observations are patchy across watersheds and climate zones. Here, we compiled 1,593 DOC observations from 40 studies spanning most Asian climate zones to map large-scale patterns, and tested hydroclimatic controls for a set of representative watersheds (Yangtze, Yellow, Mekong, Ganges-Brahmaputra, and Rajang) where sufficient time series records exist. Our findings show DOC concentrations peaking near the equator (tropical rainforest) and again above similar to 40 degrees N (humid continental dry winter), with tributaries exhibiting higher and more variable levels than mainstems. Hydroclimatic responses were basin-dependent: DOC-precipitation correlation was not significant, yet DOC significantly differed across precipitation groups with highest means at low precipitation, indicating nonlinearity and likely thresholds; temperature effects diverged by basin; and soil moisture was a consistent positive driver, especially in Mekong and Yangtze. Overall, this study highlights that DOC behavior in Asia cannot be captured by uniform assumptions across basins and climate zones. As most existing observations are limited to short-term data sets, the impacts of hydroclimatic change on carbon transport remain uncertain and require long-term data sets. Future research should take an interdisciplinary approach by integrating hydrology, geomorphology, and climate indicators by fusing remote sensing based observations and advanced analytics, to address differences in DOC behavior and climate challenges.