[A-CG42] 陸域〜沿岸域における水・土砂動態

[ACG42-04] How much suspended sediment is transported from land to oceans globally?

*鳩野 美佐子¹、芳村 圭² (1.広島大学、2.東京大学)

キーワード：全球土砂動態、数値モデリング、オセアニア

While fluvial suspended sediment plays a vital role in material transport through rivers, there are still large uncertainties in global scale estimates, partly due to its high regional dependency and lack of comprehensive observation networks. There have been several attempts to assess the global suspended sediment load to the oceans including regions with insufficient observation data by extrapolating the relationship between regional characteristics and suspended sediment load in data-rich regions. Milliman and Farnsworth (2011) compiled annual suspended sediment load data for over one thousand river basins globally, and combined various data such as elevation, precipitation, and geological features to estimate the annual suspended sediment load for river basins without observation data. The most significant are the rivers in the cluster of small islands in Oceania which is estimated to transport 6800 Mt/yr, approximately 35% of the global sum. This is significantly large considering the 13 rivers in this region included in the original database account for only 290 Mt/yr. To evaluate its validity, we used our global sediment dynamics model at 0.5 degree spatial resolution to compare the annual suspended sediment load to oceans. We found that the total suspended sediment load from this region in our model was less than a third of the previously estimated value even when calibrating model parameters to fit the annual suspended sediment load of the observed 13 rivers. Here we discuss the source of the large discrepancy in the region by comparing our model results with previous extrapolated estimates in river basins with insufficient data and its impact on the global suspended sediment load.