The erosivity factor in the universal soil loss equation (USLE) provides an effective means of evaluating the erosivity power of rainfall. The present study proposes three regression models for estimating the erosivity factor based on daily, monthly, and annual precipitation data of rainfall station network, respectively. The validity of the proposed models is investigated using a dataset consisting of 16,560 storm events monitored by 55 rainfall stations in southern Taiwan. The results show that, for 49 of the 55 stations, a strong positive correlation false(r2>0.5false) exists between the annual rainfall amount and the annual rainfall erosivity factor. In other words, the estimation model based on the annual precipitation data provides a reliable means of predicting the long-term annual rainfall erosivity in southern Taiwan. Furthermore, the root mean square error (RMSE) and mean absolute percentage error (MAPE) analysis results show that the estimation models based on annual and monthly precipitation data have a more accurate prediction performance than that based on daily precipitation data.
Soil aggregates are among crucial factors for determining both the quality and erosion resistance of soils. Biochar is a soil amendment that has seen increasing use to improve specific soil properties, mainly the physical structure and the preserving capacity of water and nutrients, as well as sequestration of soil organic carbon. In this study, we applied the rice husk biochar (RHB) and cattle manure compost (COM) in a sandy loam rural soil, which is widely distributed in southern Taiwan, to investigate the combined effects of the biochar and compost on soil aggregation and dynamic change of organic carbon fractions. Through our incubation experiment, both biochar and compost could promote the soil aggregation after eight weeks incubation. The total amounts of macroaggregates (MaAs, >2.0 mm) and mesoaggregates (MeAs, 0.25–2.0 mm) increased by 1.3–9%. During aggregation processes, a considerably greater amount of the soil organic carbon was found to enrich mainly in MaAs and MeAs in all treatments. The COM addition in the soil further promotes organic carbon enrichment in microaggregates (MiAs, <0.25 mm) + fine particles and MeAs after incubation. Increasing labile organic C (LOC) fractions were significantly found in MaAs and MeAs during aggregation processes, whereas decreasing LOC fractions were found in MiAs. The input of fresh organic matter (RHB and COM) initial acts as binding agents in MiAs, and then further enhances the formation of MeAs and MaAs gradually. In conclusion, RHB promotes the physical protection of organic C by increasing soil aggregation and is hence a management option to enhance the C sequestration potential.
<p>There are almost 24% of total remoted mountainous communities located in Chiayi, Tainan, Kaohsiung and Pingtung counties/cities of southern Taiwan. During recent years, the extreme rainfall events brought huge amounts of rainfall and triggered severe environmental disasters such as landslides, debris flows, flooding and sediment disasters in southern Taiwan. The maximum rainfall of typhoon Morakot in August 2009 was approaching 3,000 mm during 4 days in mountainous area of Chiayi city. There are 359 landslides occurred nearby the remoted mountainous communities in the study area during the typhoon event. The landslide area was over 900 ha.</p><p>The potential assessments of environmental disasters for 38 remoted mountainous communities nearby the riverbank were analyzed. The landslide areas nearby the 38 communities in last 10 years (2007-2016) were identified. The numerical models (HEC-RAS, CCHE-2D and FLO-2D) were used to simulate the flooding level, scouring and deposition of river bed and the influence area of debris-flow occurrence under different return periods (25, 50 and 100 years). The results show that there are 5, 4 and 14 high potential communities of landslide, flooding and debris flow disasters, respectively. The results proposed by this study can provide the disaster risk management of administrative decisions to lessen the impacts of environmental disasters for remoted mountainous communities nearby the riverbank in southern Taiwan under climate change.</p>
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