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Slope–velocity equilibrium is hypothesized as a state that evolves naturally over time due to the interaction between overland flow and surface morphology, wherein steeper areas develop a relative increase in physical and hydraulic roughness such that flow velocity is a unique function of overland flow rate independent of slope gradient. This study tests this hypothesis under controlled conditions. Artificial rainfall was applied to 2 m by 6 m plots at 5, 12, and 20 % slope gradients. A series of simulations were made with two replications for each treatment with measurements of runoff rate, velocity, rock cover, and surface roughness. Velocities measured at the end of each experiment were a unique function of discharge rates, independent of slope gradient or rainfall intensity. Physical surface roughness was greater at steeper slopes. The data clearly showed that there was no unique hydraulic coefficient for a given slope, surface condition, or rainfall rate, with hydraulic roughness greater at steeper slopes and lower intensities. This study supports the hypothesis of slope–velocity equilibrium, implying that use of hydraulic equations, such as Chezy and Manning, in hillslope-scale runoff models is problematic because the coefficients vary with both slope and rainfall intensity.

Large‐scale photovoltaic (PV) panel installations may significantly affect local hydrological processes, especially in hilly and mountainous regions. However, there is large uncertainty in assessing the hydrological impacts of PV power stations, as the effects of PV panel arrays on overland flow and rill erosion processes in hillslopes have been overlooked. This study quantitatively investigated the interactions between overland flow, soil loss, and rill development influenced by a PV panel array through artificial rainfall experiments on a loess slope with bare surface. The dynamics of overland flow and soil erosion processes in the slope with a four‐panel PV array were compared to a control slope. In the experiments, it was observed that the rill development in the PV slope was largely inhibited. The experiment results demonstrated that, under varying rainfall intensities, the soil erosion mass and the peak erosion rates of the PV slope was 39.7%–64.1% and 38.0%–52.5% less than the control slope, respectively. The reason for this soil erosion mitigation might be that the PV panel array attenuated the impact of rainfall by blocking raindrops, and diminished the overland flow velocity as well as its concentrating movement into rills. These reduced the erosivity of overland flow and decreased soil particle detachment and movement in the slope, which ultimately inhibited rill development and erosion. These findings provide a quantitative basis for accurately assessing the early stage environmental impact of PV power stations, suggesting that large PV installations in arid and semi‐arid regions may reduce initial soil erosion.

A global model formulation for unified weather‐climate forecast is evaluated, with emphasis on the climate simulations at typical hydrostatic resolutions. The internal sensitivity is explored by considering different dynamical configurations (resolution, solver type, transport scheme). After a basic assessment of the global mean climate, a detailed analysis of precipitation characteristics is extended to East Asia. The model shows a reasonable mean state, seasonal variation, frequency–intensity structure, and diurnal phase time. The artificial rainfall around the steep slopes of the Tibetan Plateau can be improved through choices in the dynamical configuration. The regional features characterized by “afternoon versus nocturnal‐to‐early‐morning peaks” are properly distinguished. The hourly climatic features are comparable to super‐parameterized CAM5. Different dynamical configurations demonstrate unique sensitivities related to underling physical mechanisms, which are studied from the perspective of the diurnal cycle for three representative regions. Over South China, the higher‐resolution models decrease the weak‐precipitation while increase intense rainfall, thus reducing the dry biases. This is contributed by enhanced grid and sub‐grid scale motions associated with daytime convection progression. Over central western China, the variable‐resolution model better simulates the eastward propagating episodes characterized by a transition from convective to stratiform rainfall along the eastern slope of the Plateau. This reduces the positive biases at the high topography of the Plateau and alleviates the negative biases at the lower foot. Over central eastern China, the model replicates the dominant role of large‐scale governing factors in regulating the early morning rainfall peaks, and produces stratiform heating patterns. Plain Language Summary We examine the statistical simulation of a model developed within the Global‐to‐Regional Integrated forecast SysTem, using Atmospheric Model Intercomparison Project style integration. This is among an effort in exploring a unified system for weather and climate modeling. Because of the evolutionary nature of model development, the absolute model performance can change. Thus, special attention is paid to the model sensitivity related to dynamical configurations, which helps to gain understanding that can support continuous research and development. Precipitation is one of the most important variables in a general circulation model as it encapsulates the synergistic effects of resolvable and non‐resolvable processes, the hydrological cycle, and radiative balance. Simulating precipitation faces the challenges in representing the moist physics and its interaction with dynamics. We use precipitation as performance metrics for a better understanding of the model behavior, focusing on a unique region–East Asia. The diurnal cycle is given particular emphasis because it reveals the direct physical mechanism of precipitation, and can help to disentangle the interactions between model dynamics and physics. We show that the models produce hourly rainfall features that are comparable to a global multiscale modeling framework that has two interactive dynamical solvers, and support some beneficial sensitivity. Key Points To evaluate a model formulation for unified weather‐climate forecast using the Atmospheric Model Intercomparison Project‐style experiment To understand model precipitation characteristics over East Asia by analyzing hourly scale apparent sources/sinks and grid‐scale tendencies To understand model sensitivity related to dynamical configurations, including grid resolution, moisture transport scheme and solver type

Precipitation distribution during the growing season and interannual precipitation variation may have significant impacts on grassland ecosystem productivity at the site level. To explore the effect of the distribution of precipitation on plant communities in the Inner Mongolian desert steppe dominated by Stipa breviflora , we analyzed monthly precipitation patterns during the growing season (May–October) over the past 60 years (1961–2020) and identified four major precipitation distribution patterns. These included the concentrated precipitation during July (TΛ7), August (TΛ8), and during the early and late growth stages. However, with precipitation being scarce during the boom (TM), the distribution resembled a normal distribution (T∩). Field experiments simulating the four distributions were conducted from May to October 2021. The results showed that the effects of the distribution of precipitation on plant species, diversity, and abundance were not significant; only the Pielou evenness showed a significant effect after July. The total above-ground net primary productivity (ANPP) of TΛ7 was 55.4% higher than those of the other three patterns, whereas the differences among the other three precipitation distributions were not significant. The annual forb Neopallasia pectinate was the primary contributor to the increased ANPP of TΛ7. These results suggest that the S . breviflora desert steppe achieved maximum productivity when the precipitation reached 41.6% of the annual average during July and satisfied the basic plant growth requirements during other months. This study emphasizes the implementation of management measures (irrigation or artificial precipitation) for maximizing forage yield and forecasting the plant composition in desert steppes.

There is growing evidence of a range of theoretical and applied Indigenous climate change adaptation strategies, yet analyses of African examples are generally focused at single local spatial scales, with limited description of how they have evolved over time. Drawing from research across three districts in northern Ghana, this study employs a mixed-methods approach and an interpretivist framework to develop understanding of how farmers are implementing Indigenous adaptation strategies in response to climate change risks at both household and community scales. Farmers are perceiving multiple climate risks such as increased temperatures, erratic rainfall and prolonged droughts, which are disrupting cropping calendars and decreasing productivity. In response to those impacts, farming households are utilising Indigenous knowledge to individually implement diverse strategies such as rainwater harvesting, relocation of farms to water sources, neem leaf extract and organic manure applications, while communities are collectively engaging in congregational prayers, rituals for rainmaking, taboos, investment in local irrigation systems and tree planting. Farmers’ adaptation strategies are evolving over time, as many people are integrating Indigenous practices with modern knowledge and technologies to facilitate improvements in irrigation, organic manure application, planting drought-resistant crops, agroforestry and crop diversification. Decision-makers in local, regional and national government institutions could work to design multi-scalar adaptation interventions that support the integration of Indigenous and modern knowledge to address the complexity of climate change risks across different scales to promote sustainable livelihoods.

A full-scale landslide-triggering experiment was conducted on a natural sandy slope subjected to an artificial rainfall event, which resulted in mobilisation of 130 m3 of soil mass. Novel slope deformation sensors (SDSs) were applied to monitor the subsurface pre-failure movements and the precursors of the artificially triggered landslide. These fully automated sensors are more flexible than the conventional inclinometers by several orders of magnitude and therefore are able to detect fine movements (< 1 mm) of the soil mass reliably. Data from high-frequency measurements of the external bending work, indicating the transmitted energy from the surrounding soil to these sensors, pore water pressure at various depths, horizontal soil pressure and advanced surface monitoring techniques, contributed to an integrated analysis of the processes that led to triggering of the landslide. Precursors of movements were detected before the failure using the horizontal earth pressure measurements, as well as surface and subsurface movement records. The measurements showed accelerating increases of the horizontal earth pressure in the compression zone of the unstable area and external bending work applied to the slope deformation sensors. These data are compared to the pore water pressure and volumetric water content changes leading to failure.

Abstract From June 10 to 13, 2019, continuous heavy rainfall occurred in Longchuan County, Guangdong Province, yielding a cumulative rainfall of nearly 270 mm. The heavy rainfall triggered a large number of landslide disasters and formed three hardest-hit areas. In this paper, Mibei village, Beiling town, Longchuan County, is chosen as the research object; detailed field investigation data, satellite remote sensing images, rainfall monitoring data, and artificial rainfall physical model test results are integrated; the temporal and spatial distribution characteristics of rainfall-induced group-occurring landslides in the study area are obtained; and the rainfall instability mechanism of granite residual soil slopes is explained. Under the influence of continuous heavy rainfall from June 10 to 13, 2019, 327 landslides developed in Mibei village, Beiling town, and these landslides were mainly distributed in low mountainous areas, of which the sections at elevations from 300 ~ 400 m and slopes ranging from 35 ~ 45° were the most susceptible to landslide disasters. Continuous rainfall on June 10 and 11 was the controlling factor leading to these large number of landslides, with numerous landslides occurring from 20:00 on June 11 to 04:00 on June 13. These group-occurring landslides exhibited the characteristics of a considerable rainfall lag. The deformation and failure characteristics of the numerous observed landslides within the study area were highly similar, mainly involving traction sliding failure, and the sliding mass thickness ranged mostly from 1.5 ~ 3 m. The flow pattern characteristics of unconsolidated deposits after landslide instability were significant. According to the deformation and failure characteristics of landslides and the rainfall infiltration pattern, the development of landslides was divided into stages in this paper. Due to the difference between the rainfall intensity and permeability of granite residual soil, the main influence depth of heavy rainfall was limited to the superficial zone of slopes, which is the main reason why the shallow surface zone was damaged by landslides. Under the action of continuous heavy rainfall, a saturated seepage field was established in the shallow surface zone of slopes. Driven by gravitational potential energy, this led to an uneven distribution of the slope saturation zone. Attenuation of the mechanical strength of saturated soil reduced the slope stability, and sliding failure consequently occurred in the shallow surface saturation zone. In regard to excavated slopes, anti-sliding force reduction and free face formation enhanced the slope’s susceptibility to sliding failure under the influence of heavy rainfall, which is also the reason for the large-scale distribution of landslides along the X158 county road.

The events of landslides induced by the combined effect of earthquakes and rainfall are more dangerous than those induced by earthquake or rainfall. The Yongguang loess landslide induced by the Minxian–Zhangxian Ms 6.6 earthquake in 2013 is a typical example of a landslide induced by the combined effect of an earthquake and rainfall. A few scholars have carried out relevant research on this landslide, but the initiation mechanism of this kind of landslide has not been elucidated. Therefore, the initiation mechanism of loess landslide under the combined effect of earthquakes and rainfall is studied through indoor geotechnical tests, shaking table slope model tests and numerical simulations. The indoor geotechnical tests show that the mechanical properties of Q3 loess would change significantly (the mechanical strength would decrease sharply) when soaked in water and that its strength would be further lowered under dynamic action. The slope model test results show that the infiltration depth at the slope top is deeper than that of the slope surface after continuous heavy artificial rainfall and that the natural frequency of the shoulder of the front edge of the slope top is closer to the frequency of the loading wave than it is in other parts of the slope; so the amplification effect of the seismic ground motion at the shoulder of the front edge of the slope top is more significant and the soil damage is more serious under seismic dynamic action. With the rapid increase in the residual deformation and pore water pressure of the soil mass, the loess properties change substantially, that is, loess liquefaction occurs when the pore water pressure and residual deformation reach a certain threshold. Under the action of the subsequent seismic ground motion, the liquefied loess mass of the front edge of the slope top rushes out along the sliding bed and slides down the slope surface in the form of a loess mudflow; that is, a mudflow-like loess landslide is induced. A simplified mechanical model is used in the numerical simulation test and can reproduce the triggering process of this kind of loess landslide. In this research, the initiation mechanism of mudflow-like loess landslide induced by the combined effect of earthquakes and rainfall is revealed by comprehensively considering a variety of test results, and a sliding distance calculation formula is proposed, providing a foundation for the prevention and control of this kind of landslide disaster.

Rainfall-induced landslides are a significant hazard in many areas of loess-covered terrain in Northwest China. To investigate the response of a loess landslide to rainfall, a series of artificial rainfall experiments were conducted on a natural loess slope, located in the Bailong River Basin, in southern Gansu Province. The slope was instrumented to measure surface runoff, pore water pressure, soil water content, earth pressure, displacement, and rainfall. The hydrological response was also characterized by time-lapse electrical resistivity tomography. The results show that most of the rainfall infiltrated into the loess landslide, and that the pore water pressure and water content responded rapidly to simulated rainfall events. This indicates that rainfall infiltration on the loess landslide was significantly affected by preferential flow through fissures and macropores. Different patterns of pore water pressure and water content variations were determined by the antecedent soil moisture conditions, and by the balance between water recharge and drainage in the corresponding sections. We observed three stages of changing pore water pressure and displacement within the loess landslide during the artificial rainfall events: Increases in pore water pressure initiated movement on the slope, acceleration in movement resulting in a rapid decrease in pore water pressure, and attainment of a steady state. We infer that a negative pore water pressure feedback process may have occurred in response to shear-induced dilation of material as the slope movement accelerated. The process of shear dilatant strengthening may explain the phenomenon of semi-continuous movement of the loess landslide. Shear dilatant strengthening, caused by intermittent or continuous rainfall over long periods, can occur without triggering rapid slope failure.

Preferential flow in the unsaturated zone strongly influences important hydrologic processes, such as infiltration, contaminant transport, and aquifer recharge. Because it entails various combinations of physical processes arising from the interactions of water, air, and solid particles in a porous medium, preferential flow is highly complex. Major research is needed to improve the ability to understand, quantify, model, and predict preferential flow. Toward a solution, a combination of diverse experimental measurements at multiple scales, from laboratory scale to mesoscale, has been implemented to detect and quantify preferential paths in carbonate and karstic unsaturated zones. This involves integration of information from (1) core samples, by means of mercury intrusion porosimeter, evaporation, quasi-steady centrifuge and dewpoint potentiometer laboratory methods, to investigate the effect of pore-size distribution on hydraulic characteristics and the potential activation of preferential flow, (2) field plot experiments with artificial sprinkling, to visualize preferential pathways related to secondary porosity, through use of geophysical measurements, and (3) mesoscale evaluation of field data through episodic master recession modeling of episodic recharge. This study demonstrates that preferential flow processes operate from core scale to two different field scales and impact on the qualitative and quantitative groundwater status, by entailing fast flow with subsequent effects on recharge rate and contaminant mobilizing. The presented results represent a rare example of preferential flow detection and numerical modeling by reducing underestimation of the recharge and contamination risks.