Variations In Rainfall Intensity Research Articles

Validation of TRMM and GPM Satellite Data Using Daily Precipitation Observations

Accurate precipitation data holds immense significance in hydrological analysis. A common challenge in this field often stems from the lack of comprehensive data availability. High-resolution satellite-based precipitation measurements covering large areas offer a potential solution. However, disparities in the resolution of observed rainfall data can impact data accuracy. The main goal of this study is to evaluate the accuracy of rainfall data obtained from the TRMM and GPM satellites in the Kuranji watershed. The evaluation was conducted on the performance of the GPM IMERG-F from the Integrated Multi-satellite Retrievals for the GPM mission and the TRMM 3B42RT on a daily scale spanning from 2015 to 2019 over the Kuranji watershed. The daily precipitation measurements were validated using three widely used statistical metrics (R, RMSE, and RB). The precipitation detection capability (POD, FAR, and CSI) was also considered in this assessment. The findings demonstrate that both satellite estimations exhibit a substantial correlation coefficient (0.68 for GPM, 0.62 for TRMM) with the measurements obtained from gauges, along with an inclination to overestimate precipitation. GPM IMERG-F and TRMM 3B42RT manifest a consistent spatial pattern in daily precipitation distribution, effectively representing the observed precipitation distribution. The greater probability of detection (POD), critical success index (CSI), and lower false alarm ratio (FAR) exhibited by GPM IMERG-F at varying rainfall intensities suggests its superior performance in accurately identifying observed precipitations. This finding supports the preference for GPM IMERG-F data over TRMM 3B42RT data across various applications, hydrology, and related disciplines in the future.

Instability evolution of expansive soil slope due to short duration-varying intensities of rainfall

This study examines the evolution of instability in induced expansive soil slopes under varying rainfall intensities. The destabilization evolution of expansive soil slopes and their stability under three different rainfall intensities were revealed through indoor modelling and numerical simulation. The findings indicate that slopes are not destabilized by short duration and low rainfall intensity alone. Slope failure under strong rainfall intensity follows a three-stage evolutionary process. As rainfall intensity increases, the slope's water content, soil pressure, and pore water pressure increase. However, the stress at each monitoring point of the slope affected by rainfall follows a different pattern. Under low rainfall intensity, the water content of the slope surface is higher than that of the slope foot. Under strong rainfall conditions, the water content of the slope foot is higher than that of the slope surface. Therefore, it is important to implement seepage prevention measures on the slope surface and drainage measures on the slope foot to ensure slope stability. Rainfall affects the soil pressure at each monitoring point of the slope, causing unloading on the slope surface and fluctuation at the foot of the slope. This phenomenon becomes more pronounced with increasing rainfall intensity. Numerical simulation confirms that the overall horizontal displacement distance of the slope increases with rainfall intensity, but the horizontal displacement range becomes shallower. The slope's maximum horizontal displacement occurs at its foot, with values of 0.29 m and 0.34 m under moderate and heavy rainfall, respectively, representing a growth rate of 17 %. Settlement of the slope under different rainfall intensities was greatest at the top of the slope area. The lateral stresses generated by the settlement resulted in soil uplift at the leading edge of the slope.

Limit Equilibrium Method Based Slope Stability Analysis of One of the Most Highly Landslide Susceptible Region of Guwahati

Abstract: Guwahati, situated in a hilly region, faces the constant threat of landslides due to its susceptibility to high rainfall. The city has a history of several instances of landslides, causing substantial loss of life and property. The Assam State Disaster Management Authority (ASDMA) has identified at least 366 locations within the city as highly seismic-prone areas. In response to this, a comprehensive analysis of slope vulnerability has been initiated. One of the targeted sites, recently affected by landslides, is undergoing thorough examination using the Limit Equilibrium Method (LEM). To achieve this, a detailed survey of the slope profile has been conducted, including the collection of geological data and soil samples. The geotechnical parameters are being meticulously analysed based on the obtained soil test reports, considering factors such as drainage conditions and historical rainfall intensity data. This crucial information serves as input for a LEM-based software, which is commonly available for slope stability analysis. The software utilizes sophisticated algorithms to assess the vulnerability of the slope under varying rainfall intensities, offering valuable insights into potential landslide risks. By combining field surveys, geotechnical testing, and advanced software analysis, this comprehensive approach aims to provide a holistic understanding of slope stability, aiding in the formulation of effective strategies for landslide mitigation in the identified vulnerable regions of Guwahati. This initiative aligns with the broader goal of enhancing disaster preparedness and resilience in the face of natural hazards in the region.

Sub-daily scale variations and trends in southwest monsoon rainfall over the West coasts of India and Myanmar

The West Coast of India (WCI) and the West Coast of Myanmar (WCM) receive a good amount of monsoon rainfall due to the orographic lifting and moisture transport from the neighbouring sea. Here, diurnal variation in rainfall amount, frequency, intensity, and contribution during the summer monsoon period was studied using TRMM 3 hourly precipitation data. The analysis was carried out over lowland, midland and highland regions of both the coasts. The subregions exhibit a similar diurnal pattern even though the intensity and frequency of rainfall vary from region to region. Generally, bimodal variations with late afternoon and early morning peaks are found over lowland and midland regions of both WCI and WCM in rainfall frequency, amount and contribution. However, highland regions exhibit unimodal variation with a single late afternoon peak. Over WCI, lowland regions exhibit primary peak during early morning, whereas lowlands of WCM exhibit primary peak during afternoon hours. Rainfall intensity exhibits a different pattern compared to other parameters. Rainfall intensity increases from south to north over both the coasts. Among the subregions, maximum rainfall intensity is found over midlands and minimum over highlands. In general, more rainfall is observed over subregions of WCM than subregions of WCI. Most of the lowland and midland regions, exhibit a significant increasing trend in rainfall frequency and contribution at morning hours and a significant decreasing trend at afternoon hours. Rainfall frequency exhibit different periodicities during different time indicating interannual heterogeneity in rainfall. The diurnal pattern of summer monsoon rainfall over the Indian and Myanmar West coasts shows remarkable latitudinal and topographical variations.

Experimental Study on Runoff and Sediment Production of the Fully Weathered Granite Backfill Slope under Heavy Rain in Longling, Yunnan Province

Heavy or intermittent rainfall can cause slopes to become unstable and erode, resulting in significant damage, loss of life, and destruction of property. Targeted management solutions are based on an analysis of slopes’ flow generation and sediment production patterns during periods of rainfall. This study used a fully granite backfill slope as its research subject and examined the features of slope erosion during intermittent rainfall. We examined the processes of slope flow generation and soil erosion during intermittent rain through indoor artificially simulated rainfall experiments. Three intermittent rainfall events with a 220 mm/h intensity were designed during the experiment. Each rainfall event lasted for 60 min, with an interval of 60 min between the events. By analyzing multiple rainfall events, this study reveals the patterns of runoff and sediment yield on different slopes in response to variations in rainfall intensity and slope gradient. The runoff volume on other slope surfaces exhibits a similar pattern in reaction to changes in rainfall events. As the frequency of rainfall events increases, the surface runoff tends to be higher. Additionally, with variations in slope steepness, the runoff volume generally follows an increasing trend. Notably, the slope with a 20° incline shows the smallest runoff volume. The sediment yield on different slope surfaces gradually increases as the slope increases. In particular, on a 20° slope, the sediment yield experiences a substantial increase, indicating that the impact of the slope on the sediment yield becomes more pronounced. In different rainfall events, the morphology of the slope changes due to the influence of gravity and hydraulics, resulting in oscillations in both the average runoff rate and sediment yield. Furthermore, as the slope steepens, the amplitude of these oscillations increases. The process of slope erosion involves three stages: raindrop splash erosion, runoff erosion, and collapse damage. The sequence of slope damage locations is as follows: footslope, mid-slope, and hilltop. For the backfilled slope of completely weathered granite, the artificial slope can be controlled to around 20°. Erosion on the slope mainly occurs after the formation of gullies, and slope management should focus on preventing gully formation before it happens.

Performance Verification of Autonomous Driving LiDAR Sensors under Rainfall Conditions in Darkroom.

This research aims to assess the functionality of the VLP-32 LiDAR sensor, which serves as the principal sensor for object recognition in autonomous vehicles. The evaluation is conducted by simulating edge conditions the sensor might encounter in a controlled darkroom setting. Parameters for environmental conditions under examination encompass measurement distances ranging from 10 to 30 m, varying rainfall intensities (0, 20, 30, 40 mm/h), and different observation angles (0°, 30°, 60°). For the material aspects, the investigation incorporates reference materials, traffic signs, and road surfaces. Employing this diverse set of conditions, the study quantitatively assesses two critical performance metrics of LiDAR: intensity and NPC (number of point clouds). The results indicate a general decline in intensity as the measurement distance, rainfall intensity, and observation angles increase. Instances were identified where the sensor failed to record intensity for materials with low reflective properties. Concerning NPC, both the effective measurement area and recorded values demonstrated a decreasing trend with enlarging measurement distance and angles of observation. However, NPC metrics remained stable despite fluctuations in rainfall intensity.

Spatial Heterogeneity of Summer Rainfall Trends over the Tibetan Plateau Contributed by Different Rainfall Intensities

Recent years have witnessed contrasting trends in summer total rainfall (STR) over the Tibetan Plateau (TP), with an increase in the northern and a decrease in the southern TP. This study identifies four significant centers of rainfall trends: eastern TP (“region A”), Qiangtang Plateau (“B”), Qaidam Basin (“C”), and the northern foothills of the Himalayas (“D”). Heavy rainfall dominates STR trends in regions A and D, accounting for 55.6% and 52.0%, respectively. In region B, moderate and light rainfall contribute almost equally, accounting for 37.3% and 44.8% of the STR trend, respectively. Region C is primarily influenced by light rainfall, explaining 71.2% of the STR trend. Notably, the contributions of different rainfall intensities to STR in each region vary annually, with region A experiencing more heavy rainfall, region B having moderate dominance but less light rainfall, and region C and D showing reduced and increased light rainfall contributions, respectively. Mechanistically, the strengthening of the upper-level westerly jet and the South Asian High, coupled with changes in moisture transport and convective available potential energy, collectively cause variations in rainfall intensity, characterizing the spatial heterogeneity in STR in the TP.

Laboratory study of the effect of vegetation and gravel on runoff parameters under variable rainfall intensities

Abstract The present study aims to evaluate the performance of the impervious surface as a control (O), sandy loam substrate (SL), gravel (G), gravel with geocell layer (GGE), rosemary (R), rosemary with geocell layer (RRE), turf (T), and turf with geocell layer (TGE) in the reduction of runoff volume, time-to-start runoff (TR), runoff coefficient (C), time-to end runoff (TER), peak flow rate (PF), time to peak (TP), and time base (TB) in the laboratory dimension under three different scenarios of rainfall intensity and two different slopes using a rainfall simulator. The results revealed a significant difference between the data at the level of 5% in all cases. Generally, three rainfall scenarios for all hydrological parameters TR, TER, TP, TB, C, and PF were classified into different groups. In all cases, GGE treatment performed better than that of the rest of the test groups in reducing runoff and cumulative volume. Further, treatments O and GGE experienced the highest and lowest flow rates, respectively. For a specific scenario of rainfall intensity and slope, the value of C is the lowest for GGE treatment. Finally, the implementation of geocell in the pavements was able to delay the time to start runoff.

Reliability analysis of geosynthetic-reinforced slopes under rainfall infiltration

The rainfall-induced instability of geosynthetic-reinforced is a time-dependent phenomenon owing to the infiltration process, and is influenced by rainfall patterns. Catering to the inherent uncertainty in soil properties, this study conducted a reliability analysis of three-dimensional (3D) vertical geosynthetic-reinforced slopes, in order to explore how the probabilistic stability of slope evolves over time under different rainfall patterns. A 3D horn-like mechanism incorporating the Conte-Troncone (CT) model is adopted as a framework for deterministic analysis. Through a Fourier transform-based theoretical reasoning, the CT model assesses the time-variable pore-water pressure of soils in response to any continuously varying rainfall intensity over time. Subsequently, the pore water pressure-driven changes in soil unsaturated strength and the corresponding extend power are integrated into the three-dimensional mechanism, enabling a rapid determination of the instantaneous safety factor at discrete time instants. To avoid the tedious computation generated by Monte Carlo simulation, a simplified Hasofer-Lind-Rackwitz-Fiessler (HLRF) algorithm is used to calculate the time-varying reliability indices. Using the implantation of the proposed method, the effects of rainfall pattern, slope width, and reinforcement tensile strength are investigated by parametric analysis.

A Modified SCS Curve Number Method for Temporally Varying Rainfall Excess Simulation

The SCS curve number (SCS-CN) method has gained widespread popularity for simulating rainfall excess in various rainfall events due to its simplicity and practicality. However, it possesses inherent structural issues that limit its performance in accurately simulating rainfall excess and infiltration over time. The objective of this study was to develop a modified CN method with temporally varying rainfall intensity (MCN-TVR) by combining a soil moisture accounting (SMA) based SCS-CN method with the SMA method in the Hydrologic Engineering Center’s Hydrologic Modeling System (HEC-HMS). In the MCN-TVR, the SMA-based SCS-CN method is utilized to simulate the cumulative rainfall excess and infiltration, while the SMA method in the HEC-HMS serves as an infiltration control function. A key advantage of the MCN-TVR is that it eliminates the need for additional input parameters by inherently linking the parameters in the two SMA-based methods. Sixteen hypothetical 24 h SCS Type II rainfall events with different soil types and five real rainfall events for the Rush River Watershed in North Dakota were used to assess the performances of the MCN-TVR method and the SMA-based SCS-CN method. In the hypothetical simulations, the rainfall excess simulated by the SMA-based SCS-CN and MCN-TVR models was compared to that simulated by a Green–Ampt model. Discrepancies were observed between the rainfall excess simulated by the SMA-based SCS-CN and Green–Ampt models, especially for coarse soils under relatively light rainfall. However, the MCN-TVR model, incorporating an infiltration control function, demonstrated its improved performance closer to the Green–Ampt model. For all the hypothetical events, the Nash–Sutcliffe efficiency (NSE) coefficient of the rainfall excess simulated by the MCN-TVR method compared to the Green–Ampt model was greater than 0.99, while the root mean standard deviation ratio (RSR) was less than 0.03. In the real applications, the SMA-based SCS-CN model failed to provide acceptable simulation of the direct runoff for rainfall events with durations of less than the time of concentration. In contrast, the MCN-TVR model successfully simulated the direct runoff for all the events with NSE values ranging from 0.65 to 0.91 and RSR values from 0.31 to 0.56.

Morphology of Oil Palm (Elaeis guineensis Jacq.) Seedlings Under Drought Stress with Oil Palm Shell Ash and Aspergillus niger treatment

Climate change is a limiting factor that contributes to weather anomalies such as varying rainfall intensity. Weather abnormalities impact plantation crops, such as oil palm, which are very sensitive to water deficits, and inhibition of growth in the nursery phase reduces seed quality. In an effort to increase the resistance of oil palm seedlings to drought stress, palm shell ash is given because it contains high silicon (Si) ranging from 43% to 63%. Furthermore, the fungus Aspergillus niger is known to decompose and release insoluble silicon into orthosilicic acid into the soil solution, which can be absorbed by plants, This study used randomized block design with two factors drought stress factor with four level field capacity (FC) of 80%, 60%, 40% dan 20%; factor palm oil shell and Aspergillus niger 0, 10, 20, 30 g + 5 ml/polybag. The results showed that the parameter number of Aspergillus niger colonies before and after the drought stress treatment decreased, drought stress was also a significant difference in the parameters of plant height and number of leaves, while the treatment of oil palm shell ash with the addition of Aspergillus niger had no significant effect on plant height parameters and number of leaves of oil palm seedlings.

On the need to go beyond bucket modelling to evaluate NBS risk of failure under urban constraints

The need to combine simple analytical solutions to control the full spectrum of stochastic events, not just extreme rainfall events related to flood risk, in order to restore the natural water cycle has led to the adoption of probability analysis (PA) as a powerful design tool for urban drainage systems. Applications of PA to sustainable urban drainage and nature-based solution (NBS) design are numerous but often rely on a bucket modelling (BM) approach to assess the efficiency of retention and detention structures.Managing urban growth and climate change requires careful attention to 1) the shape of NBSs to fit into an existing urban grid and 2) the intensity of rainfall, which is expected to increase significantly. The BM approach is insensitive to the shape of technical solutions and the variability of rainfall intensity, so the PA was revised, coupled with a hydrodynamic modelling (HM) approach and compared with previous BM-based approaches.In the low-intensity rainfall regime, HM and BM predict completely different infiltration system (IS) overflow probabilities. In the high-intensity precipitation regime, both provide a bell-shaped probability density function of overflow volumes, although BM tends to underestimate IS overflow volumes with low shape factor and overestimate IS overflow volumes with high shape factor.

Derivation of short-term design rainfall intensity from daily rainfall data for urban drainage design using empirical equations in robe town, Ethiopia

Flooding is a significant impact that regularly affects the majority of cities/towns in developing countries due to inadequate drainage systems that were designed without considering hydrological-hydraulic efficiency caused by design rainfall intensity. Design rainfall intensity is essential to urban stormwater management systems; however, obtaining long-term, short-term design rainfall in developing countries such as Ethiopia is challenging. As a result, this study is conducted to derive short-term design rainfall intensity from daily rainfall data for Robe town using three empirical equations for urban drainage design: Indian Meteorological Method (IMD), Modified Indian Meteorological Method (MIMD), and Ethiopian Road Authority Method (ERAM). The results show that the estimated design rainfall by IMD is greater than other methods; the relationship between IMD, MIMD, ERAM, and existing ranges from 0.57 to 1.001, 1.015 to 1.218, and 0.890 to 1.027, respectively. According to the findings of this study, the design rainfall intensity of all empirical equations is not the same in all return periods and durations. Furthermore, the peak stormwater that caused flooding will vary due to variations in rainfall intensity. Thus, this study strongly suggested that the experts consider each empirical equation and select the accurate design rainfall to design adequate stormwater drainage systems for Robe Town. To manage unexpected urban inundation caused by urban development, short-duration design rainfall and other sub-catchment characteristics will need to be considered.

Evaluation of Permeable Pavement Systems for Removing Heavy Metals from Stormwater

This study examines a modified permeable pavement system (PPS) for enhanced heavy metal attenuation from stormwater. A laboratory model consisting of six PPS columns has been tested under varying rainfall intensities. The PPS structures are arranged based on the following hypotheses for enhancing heavy metal attenuation: (i) addition of a natural zeolite layer in the subbase for promoting heavy metal attenuation by adsorption and ion exchange; (ii) addition of a bark chip layer as an organic carbon source for promoting biosorption of heavy metals; (iii) maintaining a saturated zone in order to maintain the required humidity level and decrease the level of oxygen for increased biodegradation; and (iv) inclusion of thin sand layers to restrict the transport of oxygen to create an anoxic zone in the PPS and to enhance filtration. Successful treatment of metals such as Ba, Co, Mn, Ni, and Zn has been observed under various rainfall conditions using a conventional PPS. The rainfall intensity greatly influences the attenuation of Al, Cr, Cu, Mo and Sr. During heavy rains through the conventional PPS structure, chromium is found to be leached back into the infiltrate. The results indicate that by changing the subbase material and layer setting, biosorption of heavy metals can be encouraged in the PPS structure. The results of this study suggest that the PPS structure be amended by adding into its subbase a saturated region, an organic carbon donor and thin sand layers for enhanced heavy metal attenuation. Compared to the conventional structure, the proposed structure reduces Cr desorption and improves the attenuation of Al, Cu and Mo.

Study on erosion and stability of the ecological slope

Rainfall is the main influencing factor causing slope erosion, landslide, and instability in loess; thus, it is vital to comprehend the process of rainfall erosion on various slope surfaces and water penetration inside the slope. In this paper, the loess sample is from Heifangtai in Gansu Province, and triaxial shear tests were conducted on loess with roots under varying water contents to evaluate the slope-reinforcing impact of roots. The slope surface erosion process was analyzed using a soil moisture sensor and matric suction meter to monitor the variation of matric suction in the middle slope and slope foot in response to varying precipitation levels. The numerical simulation approach is utilized to analyze the fluctuation of slope stability under the effect of varying rainfall intensities and humid heat, and the analytical solution of the safety factor is compared to the model solution. The results indicate that the shortest generation time for bare slope runoff is 6 min, whereas the greatest generation time for the Bermuda grass slope is 12 min; the shorter the period, the less water penetration and the simpler it is to reach the slope erosion stage. The slope’s rise increases runoff velocity, strengthening water resistance on the slope surface. When the test slope is 30°, the maximum mass of scouring sediment on the bare slope is 15.2 g from 24 to 36 min, compared to 14.7 g from 24 to 36 min when the test slope is 60°. The amount of scouring reduces as the slope increases. The slope safety factor declined from 3.51 to 2.84 after 24 h of heavy rain, and the loss rate accelerated as the rainfall intensity increased.

A novel grid cell–based urban flood resilience metric considering water velocity and duration of system performance being impacted

Flood risks are increasing due to climate change and urbanization. To alleviate flooding problems, the development of flood resilience is necessary. However, existing metrics based on the system performance curve and grid cells only consider the impacts of the water depth. The system performance thresholds are typically determined based on expert experience and study area conditions, resulting in the subjectivity of resilience metrics. This study proposes a novel flood resilience metric that considers the water velocity and duration of system performance being impacted. The Flood Hazard rating index and incipient velocity were used to objectively determine system performance thresholds. The system performance of traffic land was determined by considering the instability mechanisms of residents and vehicles during floods. The proposed metric was evaluated in the Minzhi region of Shenzhen City, China, under different rainfall intensities. Comparisons with an existing metric were conducted, and the contributions of flood resilience area loss of different land-use types under different rainfall intensities were analyzed. The results suggest that an increase in rainfall intensity reduces flood resilience; the higher the rainfall intensity, the longer the flood impact duration is in the study area and in different land-use types. Floods and rainfall intensity have larger influences on traffic land than on other land-use types. The proposed metric provides better performance for quantifying the impacts of floods than the existing metric. Under the rainfall intensity variation, the land-use type with the greatest impact on the overall flood resilience changes from residential land to traffic land. A decrease in the flood resilience of greenspace contributes the least to a decrease in the overall flood resilience. Traffic land should be the priority land-use type in flood resilience improvement projects. The results of the in-depth analysis of urban flood resilience assessment in this study provide reference for flood mitigation and risk reduction.

Impacts of climate change on IDF curves for urban stormwater management systems design: the case of Dodola Town, Ethiopia.

Climate change impacts are one of the global challenges that change the intensity and frequency of rainfall. The Dodola town has previously experienced rainfall-induced flooding effects, and future floods may be more frequent and severe due to possible variations in rainfall intensity due to climate change. In this study, the rainfall intensity-duration-frequency (IDF) curves are updated for the design of urban stormwater drainage infrastructures under climate change to reduce flooding risks. To assess the variations in the rainfall intensity, the future IDF curves for the periods (2020-2100) and two GCMs (CanESM2 and HadGEM2-ES) were derived and compared to the current IDF curves. It was found that rainfall intensities for future climate conditions will differ from the current period for all durations and return periods. The comparison results show that the relative change between future rainfall intensities and historic rainfall ranges from 1.5 to 30.6%, 2.48 to 42.6%, and 3.7 to 23.24% for 2020-2040, 2041-2070, and 2071-2100, respectively. The IDF relationships revealed that as a result of climate change, urban flooding will increase in the future. This study will help to better understand the impacts of climate change on rainfall IDF relationships, as well as have implications for the design of current and future stormwater management systems in Dodola, Ethiopia.

Modeling urban stormwater management in the town of Dodola based on landuse and climate change using SWMM 5.1

Study regionThis study was conducted in Dodola town, Ethiopia. Study focusThis study aims to examine the impacts of landuse and climate changes on peak runoff and flooding volumes, and also evaluates the effectiveness of low-impact development using SWMM 5.1. Three decades of landuse landcover were analyzed to assess the performance of the existing drainage system. Furthermore, the effect of climate change on drainage system performance was assessed using the estimated design storms from two global climate models (CanESM2 and HadGEM2-ES). New hydrological insights for regionThe trend of landuse landcover analysis shows that the town has experienced a significant increase in the impervious surface area ranging from 59.73 % to 86.01 %. In response to urbanization, the trend of peak stormwater showed a continuously increasing trend. The field observations confirm that the landuse change has had a significant impact on the performance of stormwater drainage systems. The study also found that the peak runoff and flooding volume of the study area was increased under separate and combined effects of rainfall intensity variation due to climate change and increased impervious surface area. This finding indicates that existing drainage systems flooded due to discharge exceeding the design capacity and that profit is required when considering the effects of both land-use and climate change scenarios. Three environmentally friendly low-impact development approaches: bio-retention, permeable pavement, and a combination of the two are applied to reduce increased peak stormwater and mitigate flooding problems.

Effects of rainfall and the slope gradient on the soil and water loss in a purple soil area

Soil and water losses in purple soil area is becoming an increasingly severe problem, bringing enormous challenges to environmental protection in rural areas. In this study, simulated rainfall experiments were conducted to analyse the effects of rainfall and the slope conditions on the soil and water loss. Purple soil from a typical slope in the Beibei District of Chongqing was selected as the experimental soil. Twenty rainfall scenarios with varying rainfall intensities and slope conditions were created in the simulation. The results indicate that the runoff initiation time shortened with an increased rainfall intensity and slope gradient. There was a logarithmic relationship between the effect of the rainfall amount on both the runoff intensity and sediment yield intensity. Generally, both the runoff and sediment yield showed a positive linear relationship with the rainfall intensity under different slope gradient conditions. In terms of the same rainfall intensity, both the runoff intensity and sediment yield intensity increased with the slope. Furthermore, a critical slope gradient for the soil and water loss was found between 20° and 25°. This study aimed to provide a reference for soil and water conservation research in a purple soil area.

A time-varying distributed unit hydrograph method considering soil moisture

Abstract. The distributed unit hydrograph (DUH) method has been widely used for flow routing in a watershed because it adequately characterizes the underlying surface characteristics and varying rainfall intensity. Fundamental to the calculation of DUH is flow velocity. However, the currently used velocity formula assumes a global equilibrium of the watershed and ignores the impact of time-varying soil moisture content on flow velocity, which thus leads to a larger flow velocity. The objective of this study was to identify a soil moisture content factor, which, based on the tension water storage capacity curve, was derived to investigate the response of DUH to soil moisture content in unsaturated areas. Thus, an improved distributed unit hydrograph, based on time-varying soil moisture content, was obtained. The proposed DUH considered the impact of both time-varying rainfall intensity and soil moisture content on flow velocity, assuming the watershed to be not in equilibrium but varying with soil moisture. The Qin River basin and Longhu River basin were selected as two case studies, and the synthetic unit hydrograph (SUH), the time-varying distributed unit hydrograph (TDUH) and the current DUH methods were compared with the proposed method. Then, the influence of time-varying soil moisture content on flow velocity and flow routing was evaluated, and results showed that the proposed method performed the best among the four methods. The shape and duration of the unit hydrograph (UH) were mainly related to the soil moisture content at the initial stage of a rainstorm, and when the watershed was approximately saturated, the grid flow velocity was mainly dominated by excess rainfall. The proposed method can be used for the watersheds with sparse gauging stations and limited observed rainfall and runoff data.