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Land surface models are increasingly used to simulate land surface processes at hyper‐spatial resolutions (e.g., ∼1 km). As model resolution increases, grid‐scale topographic effects on surface radiation fluxes and their interactions between adjacent grids become more pronounced. However, current land surface models routinely neglect the fine‐scale topographic effects on surface radiation balance. This study developed physically‐based and computationally‐efficient parameterizations (fineTOP) that explicitly resolve fine‐scale topographic effects on downward shortwave and longwave radiation as well as land surface radiative properties. The newly developed parameterizations were implemented and tested in the Energy Exascale Earth System Model (E3SM) Land Model (ELM). Multi‐decadal km‐resolution ELM simulations over the California Sierra Nevada show that fine‐scale topography significantly impacts the surface energy balance and snow processes across seasons. Slope determines the magnitude of topographic effects, while aspect controls their sign. For slopes larger than 30°, topography‐induced change in annual surface temperature can be as large as 3.3 K. Regionally, the mean value and standard deviation of topography‐induced changes in annual surface temperature are −0.22 ± 0.38 K and +0.25 ± 0.37 K over north‐facing and south‐facing slopes, respectively. Topography‐induced changes in surface radiative properties account for 3.5% ± 13.8% of total topographic effects on annual net radiation. With fineTOP, ELM captures the aspect‐dependence of snow cover fraction, snow water equivalent, and land surface temperature found in MODIS satellite observations and a snow reanalysis data set, while the default ELM fails to capture this phenomenon. The enhanced capability to represent fine‐scale topographic effects on surface radiation balance can be used to advance understanding of the role of fine‐scale topography in land surface processes and land‐atmosphere interactions over mountainous regions. Plain Language Summary In mountainous regions, fine‐scale topographic features, like hills and valleys, can strongly impact how sunlight and thermal energy are distributed on the Earth's surface. While such fine‐scale topographic effects have been well recognized, they remain unresolved in global‐scale land surface models. We characterized the fine‐scale topographic effects using a set of pre‐computed topographic factors in a hyper‐resolution land surface model. We show that such a pre‐computation strategy is feasible in the California Sierra Nevada, and the improved model better captures the observed patterns of snow and surface temperature. Our study supports the viability of the pre‐computation strategy and builds confidence in its application for future large‐scale modeling efforts. Key Points Represent fine‐scale topographic effects on surface radiation balance in the Energy Exascale Earth System Model (E3SM) land model (ELM) Multi‐decadal km‐resolution ELM simulations with improved parameterizations capture the contrasts between north‐ and south‐facing slopes Improved ELM simulations also capture the aspect‐dependent patterns of snow and surface temperature revealed by the benchmark data sets

In this study, the extreme rainfall event on 2 June 2017 along the northern coast of Taiwan is studied from a modeling perspective. While a peak amount of 645 mm was observed, two 1 km experiments produced about 400 and 541 mm, respectively, using different initial and boundary conditions, and thus are compared to isolate the key reasons for a higher total amount in the second run. While the conditions in the frontal intensity and its slow movement are similar in both runs, the frontal rainband remains stationary for a long period in this second run due to a frontal disturbance that acts to enhance the prefrontal southwesterly flow and focuses its convergence with the postfrontal flow right across the coastline. Identified as the key difference, this low-pressure disturbance is supported by the observation, and without it in the first run, multiple slow-moving rainbands pass through the coastal region and produce more widely spread but less concentrated rainfall, resulting in the lower peak amount by comparison. To explore and test the effects of Taiwan's topography in this event, two additional 1 km runs are also used. It is found that the removal of the terrain in northern Taiwan allowed the postfrontal cold air to move more inland and the rainfall became less concentrated, in agreement with a recent study. Also, when the entire island topography of Taiwan is removed, the result showed significant differences. In this case, the blocking and deflecting effects on the prefrontal flow are absent, and the heavy rainfall in northern Taiwan does not occur.

Vegetation indices play an important role in monitoring variations in vegetation.The Enhanced Vegetation Index (EVI) proposed by the MODIS Land Discipline Groupand the Normalized Difference Vegetation Index (NDVI) are both global-based vegetationindices aimed at providing consistent spatial and temporal information regarding globalvegetation. However, many environmental factors such as atmospheric conditions and soilbackground may produce errors in these indices. The topographic effect is another veryimportant factor, especially when the indices are used in areas of rough terrain. In thispaper, we theoretically analyzed differences in the topographic effect on the EVI and theNDVI based on a non-Lambertian model and two airborne-based images acquired from amountainous area covered by high-density Japanese cypress plantation were used as a casestudy. The results indicate that the soil adjustment factor “L” in the EVI makes it moresensitive to topographic conditions than is the NDVI. Based on these results, we stronglyrecommend that the topographic effect should be removed in the reflectance data beforethe EVI was calculated—as well as from other vegetation indices that similarly include a term without a band ratio format (e.g., the PVI and SAVI)—when these indices are used in the area of rough terrain, where the topographic effect on the vegetation indices having only a band ratio format (e.g., the NDVI) can usually be ignored.

The seismic waves do not arrive with a vertical incidence for near-fault rock slopes, which highlights the importance of investigating the topographic effect under oblique incidence seismic waves. The equivalent nodal force method was employed to simulate seismic P waves with oblique incidence, by utilizing the finite difference method and viscoelastic artificial boundary. The accuracy of the method was verified by comparing it with the analytical solution of the free field in half-space, and the error is within 5%. Furthermore, the influence of slope heights, angles, and shapes on the dynamic response of rock slopes is analysed under the different incidence angles of seismic waves. The results show that the critical height of the rock slope varies with the incident angle, and the greater the incidence angle, the lower the critical height of the slope. The maximum value of the acceleration amplification coefficient is 8.5 in the slope shoulder when both the slope angle and incident angle are 75°. Additionally, the location of the strong acceleration response area of the concave and linear slopes is almost not affected by the incident angle, whereas the convex slopes move from the slope shoulder towards the convex position with increasing incident angle.

Ground motion model (GMM) is an important component of seismic hazard analysis in Northwestern China. The Ms 6.2 Jishishan earthquake in the Lajishan Mountain Fault zone of Northwestern China was well recorded by the densely distributed China Seismic Intensity Rapid Reporting and Earthquake Early Warning System, providing a good basis for GMM development of this region. In this study, we evaluate the applicability of five high-quality GMMs in this seismic zone, including two developed specifically for Southwest China, two from the NGA-West2 project, and one for Japan, using the records from this earthquake. We found that the NGA-West2 models and the Japan model outperform those developed for Southwest China, which exhibit significant underestimation of the attenuation effect and site effect. We examine the regional differences in ground motion attenuation and site response between the Loess region and the nonLoess region. Our findings reveal that the Loess region has significantly slower attenuation rates and stronger V S30 scaling rates than the nonLoess region at short spectral periods up to about 0.6s. Accounting for these regional differences could substantially reduce ground motion modeling errors. Additionally, a clear correlation between the ground motion residual and the topographic position index (TPI) is identified at periods longer than 0.6s. We interpret it as regional topographic effect and it is probably affected by both the surface topography and the large-scale subsurface structure. Accounting for this effect could further lead to a decrease in model variability. The results are helpful for the improvement of GMMs for Northwestern China or specifically for the Lajishan Mountain Fault zone.

Seismic site effects (topography, geology, internal fracture, et al.) and direction amplification are an important component in inducing a landslide during an earthquake. The evaluation of the dynamic response characteristics of a slope is the first and important step in earthquake engineering design and regional hazard assessment. To document the seismic response of an irregular slope, broadband seismic field monitoring seismometers were deployed along an earthquake-induced landslide Mogangling slope, on the one of important water systems in Sichuan, Dadu River. Field monitoring data reveal that ground motion is directionally amplified near 80° clockwise from North parallel to slope inclination when the frequency is between 3 and 4 Hz, at the crest of the Mogangling slope. During an earthquake, the peak ground acceleration of the M1 station (slope crest) is 5.3 times greater than the M3 station (near slope toe). The standard spectral ratio (SSR) of the slope crest/slope toe (M1/M3) reaches a value of 11.5 at 1.4 Hz, during the earthquake. A series of discrete element numerical models indicate that SSR of the field monitoring data can be reproduced considering the irregular geometry, surficial weak layer, and internal fractures. The recent Luding earthquake on 5 September 2022 with a magnitude of Ms 6.8 induced slope failure in the Mogangling slope reveals the seismic amplification effect again. Our findings can offer some important insights into the mechanism of earthquake-induced landslide and regional-scale landslide distribution.

A correlation model for the diffuse fraction was recently developed on the basis of a data set obtained in the western part of the Taiwanese mainland. However, it is widely agreed that no existing diffuse fraction correlation model is applicable to all geographical regions and climatic conditions, which is a viewpoint stated from a macro perspective. This study re-justifies this viewpoint through the consideration of a rather small geographical region: Taiwan. The topographic profile of the Taiwanese mainland primarily comprises the high-rise Central Mountain Ranges running from north–northeast to south–southwest, which separate the mainland into eastern and western parts. Furthermore, there are a number of small, remote islands around the Taiwanese mainland. The humidity over the sky dome of these small islands, carried from the moist sea (or ocean) air, is usually greater than that of the Taiwanese mainland. This results in different diffuse fraction patterns between these two geographical regions due to the climatic factor of atmospheric constituents. Two diffuse fraction correlation models for Taiwan were developed using in situ data sets for the eastern part of the Taiwanese mainland and an island in the Penghu archipelago, respectively. In particular, one case considered the topographic effect on modeling the diffuse fraction in Taiwan, while the other considered the geographical effect. Statistical assessments indicate that each correlation model developed in the present study performed better than the previous one developed using the in situ data set for the western part of the Taiwanese mainland, with both applied to the specific site where the data set was used for the model’s development. This work demonstrates the need to consider the effects of topography and geography when modeling the diffuse fraction in Taiwan.

Accurate surface heat flow data are required for a wide range of geological and geophysical applications. However, sediment temperature measurements beneath the seafloor often involve large uncertainties owing to the influence of bottom-water temperature (BWT) fluctuations. Previous studies reported apparently negative geothermal gradients in the Joetsu Basin of the Japan Sea and suggested that BWT fluctuations disturbed sediment temperatures. To address this problem, we monitored BWTs in the Joetsu Basin over a 2 year period to determine the depth at which the influence of BWT fluctuations on sediment temperature becomes negligible. Combined with sediment thermal diffusivity data, we determined that the BWT fluctuations can disturb sediment temperatures to a depth of 2 m. We obtained heat flow values of 81–88 mW m− 2 by measuring sediment temperatures at depths > 2 m using a 15 m long geothermal probe. The measured heat flow values are inversely correlated with topography owing to the effect of topographic change on the geothermal structure near the seafloor. A two-dimensional geothermal structure model was constructed to account for the topography, yielding an estimated regional background heat flow of 85 ± 6 mW m− 2. This study provides two important guidelines for obtaining accurate surface heat flow data in marine areas with large-amplitude BWT fluctuations: (1) quantitative information regarding BWT fluctuations and sediment thermal diffusivity is required to evaluate the depth range to which BWT fluctuations affect sediment temperature; and (2) information regarding the lithology and consolidation state of seafloor sediments is required for effective penetration using a long probe.

In the past five years, the local magnitude (ML) 5.8 Gyeongju and ML5.4 Pohang earthquakes have caused significant damage to the southeastern Korean Peninsula. To evaluate the ground motion recorded during these earthquakes, we compared them with the Korean ground motion models (GMMs), also known as the ground motion prediction equations (GMPEs), Next Generation Attenuation of Ground Motions (NGA) GMMs for Western U.S. and Central and Eastern North America. The ground motions exhibit amplification near a period of 0.1 s compared to the predicted spectral accelerations. These amplifications are likely to be attributed to site and topographic effects. The existing GMMs do not account for the topographic amplification which might be prevalent in the mountainous regions of Korea. Therefore, we propose correction factors for the predicted ground motions for various periods in terms of magnitude, source-to-site distance, VS30, and relative elevation. The standard deviation values of the residuals significantly decreased by applying these correction models.

The local topography hugely impacts the characteristic of earthquake ground motion, further affecting the seismic response of the train-bridge coupled system. Based on the theory of viscous-spring artificial boundary, an analytical model for a train-bridge system subjected to multi-support seismic excitations considering valley topography is established, by applying the displacement time histories of the seismic ground motion to the bridge supports. The influences of the height-to-width ratio of the valley topography, the shear wave velocity of the site soil, and the incident angle of the seismic wave on the seismic responses and running safety of the train-bridge coupled system are investigated by means of parametric investigations, with a 344 m long bridge subjected to the obliquely incident P-wave taken as a case study. The results from the case study demonstrate that the shear wave velocity of the site soil and the incident angle of the seismic wave affect the seismic responses of the train-bridge coupled system in terms of peak occurrence time. The peak values of seismic responses are mainly influenced by the height-to-width ratio of the valley topography as well as the incident angle of the seismic wave.