Quantitative understanding of potential changes in streamflow and sediment load is complicated by uncertainty related to land use change projections, which is characterized by a high uncertainty in terms of demand (quantity) and location of changes (spatial distribution). We simulate the Sesan, Srepok, and Sekong Rivers (3S), the most important tributaries of the lower Mekong River, with the Soil and Water Assessment Tool (SWAT) to investigate the implications of conversion of forest to agricultural lands. Multiple land use transitions in the 3S basin are projected using the Land Change Modeler. The uncertainty in land use projection was addressed using an ensemble forecasting approach for 2060, combining (a) three land demand scenarios, (b) two transition potential modeling approaches (i.e., approach to create maps of the likelihood for areas to transition from one land use type to another), and (c) retaining or not protected areas. Land demand leads to the greatest uncertainty in land use change projections. Transition potential modeling approaches do not make much difference in the total change, but can result in spatial variations of change. Retaining protected areas can contribute significantly to uncertainty in land use change projections. Decrease in annual streamflow of the 3S basin varied from 3% to 21%, and changes in annual sediment outflux from the basin ranged from −8% to 249% for simulated scenarios. Land use demand uncertainty results in the highest streamflow and sediment load changes and can thus have major consequences for water and sediment management strategies in areas undergoing rapid development.

中文翻译：

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土地利用变化的不确定性对快速发展地区的水流和泥沙沉积的影响：以湄公河流域为例

与土地用途变化预测有关的不确定性使对水流和泥沙负荷的潜在变化的定量理解变得复杂，其特征在于需求（数量）和变化位置（空间分布）方面的高度不确定性。我们使用土壤和水评估工具（SWAT）模拟了湄公河下游最重要的支流Sesan，Srepok和Sekong河（3S），以调查森林向农业用地转化的影响。使用Land Change Modeler可以预测3S盆地中的多个土地利用过渡。土地利用预测的不确定性通过综合预测方法解决了2060年的问题，该方法结合了（a）三种土地需求情景，（b）两种过渡潜力建模方法（即，创建区域从一种土地利用类型过渡到另一种土地利用类型的可能性的地图的方法）；以及（c）保留或不保护的区域。土地需求导致土地利用变化预测的最大不确定性。过渡电位建模方法不会在总变化中产生很大的差异，但是会导致变化的空间变化。保留保护区会大大增加土地用途变化预测的不确定性。在模拟情况下，3S盆地的年流量减少量从3％到21％不等，该盆地的年沉积物流出量变化在-8％到249％的范围内。土地利用需求的不确定性导致最大的水流量和泥沙负荷变化，从而可能对快速发展地区的水和泥沙管理策略产生重大影响。