Indonesia offers a dramatic opportunity to contribute to tackling climate change by deploying Natural Climate Solutions (NCS), increasing carbon sequestration and storage through the protection, improved management, and restoration of drylands, peatlands, and mangrove ecosystems. Here, we estimate Indonesia's NCS mitigation opportunity for the first time using national datasets. We calculated the maximum NCS mitigation potential extent using datasets of annual national land cover, peat soil, and critical lands. We collated a national emissions factor database for each pathway, calculated from a meta-analysis, recent publications from our team, and available literature. The maximum NCS mitigation potential in 2030 is 1.3 ± 0.04 GtCO2e yr-1, based on the historical baseline period from 2009–2019. This maximum NCS potential is double Indonesia’s NDC (Nationally Determined Contribution) target from the Forestry and Other Land Use (FOLU) sector. Of this potential opportunity, 77% comes from wetland ecosystems. Peatlands have the largest NCS mitigation potential (960 ± 15.4 MtCO2e yr-1 or 71.5 MgCO2e ha-1 yr-1) among all other ecosystems. Mangroves provide a smaller total potential (41.1 ± 1.4 MtCO2e yr-1) but have a much higher mitigation density (12.2 MgCO2e ha-1yr-1) compared to dryland ecosystems (2.9 MgCO2e ha-1 yr-1). Therefore, protecting, managing, and restoring Indonesia’s wetlands is key to achieving the country’s emissions reduction target by 2030. The results of this study can be used to inform conservation programs and national climate policy to prioritize wetlands and other land sector initiatives to fulfill both Indonesia’s Nationally Determined Contribution (NDC) by 2030, while simultaneously providing additional co-benefits and contributing to COVID-19 recovery and economic sustainability.
<p>Landslides are common natural hazards that greatly impact lives and property worldwide. The magnitude of landslide impacts depends strongly on how far landslide sediments travel, widely known as landslide mobility. Numerous studies showed that landslide mobility is complex, but largely affected by initial water content during landslide initiation. Here, water acts as a medium that carries the collapsed landslide mass downslope. Vegetation root systems may alter the initial water content by modifying the flow path within the soil. The mechanical reinforcement of root systems may also limit the spatial propagation of the landslide mass. Thus, vegetation root systems may exert significant effects on landslide mobility. Nevertheless, effects of root systems on landslide mobility have rarely been discussed in landslide studies. The objective of this study is to evaluate the effect of rooting systems on landslide mobility.</p><p>A flume constructed at a 1:70 scale was used to evaluate the effect of root systems on landslide mobility. The flume consisted of two segments representing landslide initiation (120 cm long, 35&#176; inclination) and deposition (150 cm long, 35&#176; inclination). All segments were 80 cm wide, 15 cm high, and constructed with 1-cm thick acrylic material. Sand (density=1.4 g/cm<sup>3</sup>, D<sub>50</sub>=0.23 mm) was placed in the initiation segment to a depth of 10 cm. For conditions with vegetation (V), we grew pea (<em>Pisum sativum L.</em>) bean sprouts in the sand to simulate the root system. Sprouts were grown at 3 cm intervals for two weeks to simulate the root system on 2200 stem/ha of Japanese cedar forest. To initiate landslides, 90 mm/h of rainfall was applied via nozzles installed at 2 m above the flume. Timing of landslide initiation was then measured. Water content was also measured by TDR sensors installed at 3 and 7 cm depths below the soil surface. The L/H ratio was estimated based on total travel distance and total descent height of the landslide mass.</p><p>Vegetated conditions (V; n=3) were more stable than non-vegetated conditions (NV; n=3). Indeed, landslides initiated at 889-959 s (SD=41 s) on V, while on NV was 510-519 s (SD=5 s). Mean volumetric water content during landslide initiation was 0.2-0.22 (SD=0.01) on V, while on NV was 0.16-0.2 (SD=0.02). Because V had higher water content than NV, V was 1.2-1.4 times more mobile than NV. The L/H was 2.2-2.4 (SD=0.09) on V, while on NV it was 1.7-1.8 (SD=0.06). In general, vegetation root systems maintain slope stability by adding more cohesion to soils. Due to this reinforcement, greater gravitational forces and pore water pressure are needed to destabilize the slope. This consequently elevates the threshold of water content for landslide initiation. Since water content greatly influences mobility, wetter conditions enhance the mobility of the collapsed landslide mass. Our findings concur with previous studies that root reinforcement can mitigate slope instability. However, we highlight that such reinforcement can also enhance the mobility, which may elevate the potential impacts of landslides. We further investigate the effect of various stem densities on landslide mobility.</p>
Earthquake-induced landslides are a major sediment disaster that can lead to significant fatalities and destruction of infrastructures [Owen et al ., 2008]. Numerous studies have investigated the characteristics of earthquake-induced landslides worldwide. By studying the 2015 Mw 7.8 Gorkha earthquake in Nepal, Roback et al . [2018] identified that slopes with gradients ranging from 40 to 50°and high-relief Himalayan mountainous topography (2500-5000 m a.s. l.) increased susceptibility to landslides. A high proportion of landslides occurred on hillslopes with gradients of 30-40°in the 2013 Mw 5.9 Minxian earthquake in China [Tian et al ., 2016]. In Japan, Koyanagi et al . [2020] demonstrated that landslides occurred on upwardly convex landforms in the 6.9 km 2 Tokosegawa watershed of the Mount Aso volcano region in the 2016 Mw 7.0 Kumamoto earthquake.The mobility of landslides is an important factor in their characterization. Guo et al . [2014] reported that the 46 landslides caused by the 2008 Mw 7.9 Wenchuan earthquake traveled for 347-4170 m depending on the slope gradient. A rainfall-induced landslide in the 2014 Oso disaster in Washington, United States, was transported for approximately 1 km because of a high water content and liquefied conditions [Iverson et al ., 2015]. Kharismalatri et al . [2017] showed that 33 deep-seated landslides traveled for 130-3310 m depending on the stream gradient and inflow angle.Vegetation ground cover is another key factor for characterizing landslides and their mobilities in
<p>Vegetation is one of key factors controlling landslide occurrence, including frequency, size, and depth. Both horizontal and vertical root networks have important roles in stabilizing hillslopes. For instance, landslide density can be moderated by dense and deep tree root reinforcement below the potential soil slip surfaces. Landslide size can be reduced by extended dense and thick tree root networks, providing cohesive and lateral hillslope reinforcement. Vegetation conditions such as density and composition also alter the landslide occurrence because they are linked to root network density and strength, which are affected by different biogeoclimatic conditions. These findings regarding landslide-vegetation interactions were mostly based on rainfall-induced landslide cases. Preliminary, but yet to be confirmed, findings in Eastern Iburi Earthquake-Induced Landslides (EIL) showed that lateral root reinforcement might moderate the size of landslide scars in forested areas compared to logged areas. &#160;Therefore, our primary objective was to examine the effect of different vegetation composition on EIL based on global data and supplemental analysis.</p><p>Our global database of EIL was compiled for a 20-yr period using a literature review and GIS analysis. Documented landslides were restricted to shallow mass movements with depths approximately less than 3 m. For vegetation-related analysis, we used Net Primary Production (NPP) and Leaf Area Index (LAI) derived from MODIS-Terra satellite images. Twenty-seven EIL cases were recorded in our database occurring from 2002 to 2018. Among these, 26% of the total cases occurred in Japan, followed by 18% for both in China and New Zealand. Based on climate types, 22% of total EIL cases occurred in temperate oceanic climate (Cfb) dominated by New Zealand EIL cases, and 15% cases occurred in humid subtropical climate region (Cfa), such as Japan. Moreover, 7% cases occurred in tropical rainforests (Af) and 7% cases in hot desserts climate regions (BWh). Among the 27 recorded cases of EIL, we selected eight EIL cases based on biomass classes, which are low (0-2 gC/m<sup>2</sup>/day), moderate (3-5 gC/m<sup>2</sup>/day), and high (>5 gC/m<sup>2</sup>/day). A power-law cumulative-area distribution of landslide areas showed that low biomass sites had the largest landslides (11,000 m<sup>2</sup>), followed by moderate biomass (3000 m<sup>2</sup>), and high biomass (200-3000 m<sup>2</sup>) with the smallest landslides, possibly associated with the density of vegetation. In low biomass regions, the average LAI was 1.8 m<sup>2</sup>/m<sup>2</sup>, which was three times lower compared to regions with higher biomass. This indicates that in regions with sparse vegetation, slope reinforcement by dense lateral root networks was minimal. Future research is focusing on compiling information on landslide scars and root depth to assess the effects of vegetation density and vertical root reinforcement on landslide characteristics in each biomass class.</p>
<p>The spatial variability of landslides and associated sediment deposits induced by earthquakes alters both short- and long-term sediment dynamics in watersheds. Linkages between landslide occurrence and sediment accumulations within channels are important for evaluating spatial and temporal dynamics of sediment from headwaters to downstream. To evaluate spatial variability of landslides, we examined landslide-area density (LAD: landslide area divided by watershed area) in different sub-watersheds (areas 0.01 to 4.4 km<sup>2</sup>) of Habiugawa watershed (40 km<sup>2</sup>), which was affected by the 2018 Hokkaido Eastern Iburi earthquake, Japan. The watershed is located 13 km north of the epicenter and is covered by secondary conifer and deciduous forest. The topography is hilly associated with long-term landform development by paleo-glacial erosion. Altitude ranges from 30 to 440 m; mean hillslope and channel gradients are 30&#176; and 10&#176;, respectively. Landslides mostly occurred at depths from 1 to 2 m below pumice layers formed by the Mt. Tarumae eruption 9000 yr ago (Ta-d), with total soil depths from 2 to 3 m. The 0.5 m LiDAR-based DEM and 0.2 m post-earthquake orthophotos were used to calculate LAD by GIS analysis. To examine spatial variability of in-channel sediment deposited by landslides, we used deposit-length ratio (DLR: total length of sediment accumulations within channels divided by total channel length within sub-watersheds). Sediment deposition in channels was assessed as rough surface topography by DEM and orthophotos.</p><p>We identified 2941 landslides: mean area=1620 m<sup>2</sup>; range from 20 to 34710 m<sup>2</sup>. LAD in the entire Habiugawa watershed was 0.12 km<sup>2</sup> km<sup>-2</sup>, which is high compared to the other earthquake-induced landslides (e.g., Wenchuan earthquake: 0.03 km<sup>2</sup> km<sup>-2</sup>). Sub-watersheds < 0.1 km<sup>2</sup> had wide ranges in LADs (0.0 to 0.8 km<sup>2&#160;</sup>km<sup>-2</sup>), while sub-watersheds from 0.1 to 0.5 km<sup>2</sup> ranged from 0.2 to 0.5. Sub-watersheds > 0.5 km<sup>2</sup> had LADs from 0.1 to 0.3. Seventy-four percent of small watersheds (< 0.5 km<sup>2</sup>) with high LADs (> 0.3) also had high sediment accumulations within gentle channels (DLR &#8805; 0.8). This suggests that poorly mobilized sediments that initiate in headwaters rapidly deposit in channels. Conversely, the other small watersheds (26%) had lower sediment accumulation within steeper channels (DLR < 0.8), suggesting that these high-mobilized sediments traveled longer and were evacuated from watersheds to some extent. Such differences in sediment mobility in small sub-watersheds (< 0.5 km<sup>2</sup>) may cause sporadic sediment accumulations within channels of larger watersheds (> 0.5 km<sup>2</sup>). Our findings suggest that geomorphic features of watersheds associated with long-term legacies of geomorphic evolution possibly affect the spatial variability of landslide occurrence and the associated in-channel sediment accumulation induced by the earthquake.</p>
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