Contrasting impacts of irrigation and deforestation on Lancang-Mekong River Basin hydrology

Irrigation expansion and subsequent deforestation substantially affect large basin variability. However, given the complex interactions between hydrological variables, a more comprehensive understanding of the hydrological impacts within the coexisting land use changes is needed. Here, we applied surface-groundwater-coupled simulations with historical river gauges and satellite observations to evaluate long-term and seasonal changes in Lancang-Mekong River Basin hydrology. Increasing irrigation elevated soil moisture but depleted groundwater storage. Conversely, deforestation reduced soil moisture, and increased lateral flow in areas with steep terrain compensated for groundwater depletion. Irrigation affected runoff by augmenting evapotranspiration and baseflow, which had opposite implications for runoff changes, causing a mixed spatial pattern of decreases and increases. Meanwhile, decreases in soil moisture due to deforestation offset increases in evapotranspiration due to irrigation, resulting in wider areas of runoff increases than decreases. These illustrate the distinct hydrological impacts of different land use changes and a pathway to complex system assessments. Impacts of irrigation and deforestation in the Lancang-Mekong River Basin are contrasting for soil moisture, groundwater, and other water variables causing complex runoff changes, according to analysis of modelling with river gauge and satellite data.