High-intensity Rainstorms Research Articles

External factors driving surface temperature changes above geothermal systems: answers from deep learning

Introduction: The surface expression of enhanced geothermal heat fluxes above an active hydrothermal system causes a surface thermal anomaly (ΔT). The thermal anomaly is expressed by the difference between the temperature within the heated zone (Th) and the temperature of non-heated surfaces (T0). Given that the resulting thermal anomaly at the surface is of extremely low magnitude (1°C–5°C at Vulcano, Italy), it is extremely sensitive to overprinting by external factors, namely, meteorological influences on surface temperature variation, such as solar heating, wind and rain.Methods: To test the sensitivity of the surface to external drivers, we installed two surface temperature measurement stations within the Vulcano’s Fossa crater, one inside the thermal anomaly and one outside (separation = 50 m), with a weather station co-located with the T0 station. Time series of Th and T0 were collected for 2020, when the Vulcano Fossa hydrothermal system was at a low and stable level of activity so that external drivers would have been the main influences on Th and T0, and hence also ΔT. To test for divergence from normality in terms of diurnal and seasonal variations in Th and T0, and the role of external factors in causing abnormality, we used the deep learning engine DITAN: a domain-agnostic framework to detect and interpret anomalies in time-series data.Results: During the year, DITAN found 16 cases of two types of meteorological events: intense low-pressure systems and high-intensity rainstorms (cloudbursts). Passage of 13 abnormal low-pressure systems were detected (10 between February and May, and three in December), with three abnormal rainstorm events (all in December); all three being coincident with the abnormal low pressure events. We find just two abnormalities in the time series for of Th and T0, both of which coincide with passage of abnormal low-pressure systems, and neither of which coincide with abnormal rain events. We conclude that diurnal and annual heating and cooling cycles, subject to normal meteorological inputs and at a surface above a geothermal-heated source, are immune to anomalous behaviour to the external (meteorological) variations.

Evaluating the Capacity of Existing Stormwater Drainage System in Kapan, Kathmandu via SWMM Mode

Overflowing drainage systems in the Nepalese cities are the most significant issue due to unplanned urban expansion and inadequate drainage networks. As the city's drainage networks are not designed to handle the extra runoff from catastrophic flooding incidents, flash floods typically occur during short-duration, and high-intensity rainstorm storms frequently. In the vicinity of Kapan, Kathmandu, and many other Nepalese cities, particularly during the rainy season, roads are seen changing into the streams. This study employs a hydrological analysis model to examine the storm water drainage system existing currently in the Kapan area. Being the EPA Storm Water Management Model (SWMM) physically based, deterministic type that simulates the inflows, outflows, and storages of water within a sub-catchment efficiently, it is chosen here mainly to model the catchments specifically. Though it has not been employed frequently in the context of Nepal, despite its popularity in the industrialized countries such as United States of America for the proper management of the storm water, the SWMM is particularly employed here to model the catchments due to its publicly available, easy to obtain, simple data input parameters, and simple processing steps in compared to other relatively more expensive yet sophisticated models. The catchment's overall area of 360.57 hectares was at first separated into the 86 sub catchments using the SWMM based on its surface elevation and existing drainage network, and the attributes of each sub-catchment were then assigned accordingly. After the proper identification of the sub-catchments, the runoff from the relevant sub-catchments was routed to the respective nodes, and finally to the outlet via conduits. In the current study, the drain system (Combined Sewer line) is given along the center of the road network. The storm network are represented by junctions, conduits, and outfalls. The longitudinal and velocity profiles of the drain were obtained. The critical runoff and capacity of existing drains were determined, as well as their validation with discharge derived using the rational technique. With the runoff generated during peak rainfall 45.08 mm/hr., the Kapan area's existing drainage system was found to be insufficient. This study suggests that the SWMM would be the most effective model to be employed for predicting the sudden surface runoff and for prior managing of the storm water, particularly in Kathmandu and other vulnerable parts of main cities in Nepal, where overflow has caused serious problems during rainfall.

Climate-smart forestry in the world’s drylands: A review of challenges and opportunities

Land degradation and desertification are widespread across the world’s drylands. These processes are substantially affected by climatic change, with long-term and severe droughts on the one hand, and high intensity rainstorms and devastating floods on the other hand. Simultaneously, land-use change and mismanagement practices have led to processes of accelerated soil erosion, depletion of soil organic carbon pools, and the degradation of extensive drylands. Forestry has been accepted as an effective means for restoring degraded drylands, and for attaining a range of regulating, provisioning, supporting, and cultural ecosystem services. Specifically, forestry is widely perceived as an effective means for soil erosion control, organic carbon sequestration, microclimate improvement, and climate change mitigation. However, forestry in drylands often proves to generate substantial environmental challenges, resulting in deterioration of ecosystem functions and health. The objective of this essay is to review the challenges and opportunities induced by dryland afforestation and reforestation, and highlight the need to attain climate-smart strategies for establishing and managing these land-uses. Particularly, tree species invasion and allelopathy, which are common in dryland forestry projects, jeopardize species richness and diversity of native vegetation communities. Further, the challenges linked with tree invasiveness necessitate predicting the distribution of potentially invasive species and foreseeing their impacts on the recipient ecosystems under projected climate change scenarios. The effect of allelopathy is significant under limited water availability conditions and is expected to be determined by the expanding drylands and intensifying aridity worldwide. Therefore, judicious selection of tree species should not only focus on ones with high water-use efficiency, low flammability, high pest resistance, and fast growth, but also on low invasiveness and allelopathic capacities. Insights of this essay may be used by land managers, stakeholders, and policy makers involved in environmental development of drylands.

Characteristics of runoff and sediment load during flood events in the Upper Yangtze River, China

Understanding the change in sediment load at a flood-event scale helps to enhance channel regulation and optimize reservoir operation. This is particularly true in the Upper Yangtze River basin where a few flood events contribute most of the annual sediment load. This paper collected field data from representative hydrological stations and applied statistical analysis to investigate the change in runoff and sediment load during flood events in the Upper Yangtze River, including both the mainstream (Jinsha River) and its major tributaries (Min, Tuo, Jialing, and Wu Rivers). The results show that flood events contribute more sediment load than runoff volume to the annual statistics. A general decreasing trend occurs in sediment load in all river basins, which is closely related to soil conservation efforts and dam construction. The series of sediment load modulus of each stations present abrupt change. The variations in sediment load modulus in low flow are more significantly than those in high flow at different abrupt-change period, indicating high flows during flood event have been found to still carry the same amount of sediment as their predecessors in the Upper Yangtze River. An “abnormal” increase in sediment load in recent years (2013–2020) has been observed at the Fushun station in Tuo River, and three factors, i.e., earthquake, high-intensity rainstorm and local scouring, were identified to be responsible for such increase. The findings of our study are helpful for better management of basin-scale sediment resources and regulation of reservoirs in the Upper Yangtze River.

Extreme Flood Levels during the Operation of Cascade Reservoirs: A Case Study of the Lower Yangtze River in 2020

Flood disasters related to climate change are becoming increasingly frequent, indicating the potential for repeated future incidence. It is essential to fully understand the causes and mechanisms of flood formation to reduce future losses. By taking the extreme flood in the lower Yangtze River in 2020 as an example and using hydrological and rainfall data of the basin, the formation process and triggering factors of a flood disaster were analyzed in this study. The flooding process can be divided into six typical stages, in which the long duration plum rain season, frequent and high-intensity rainstorms, and high overlapping rainfall areas are the preconditions for flood formation, whereas frequent encounters of floods in the main stream and tributaries of the middle and lower Yangtze River are the decisive factors. In addition, flood drainage along the lower reaches and the jacking effect of the downstream tide level play a role in promoting flooding. During this process, the joint operation of cascade reservoirs plays a key role in the prevention of catastrophic floods. The aforementioned results can provide a reference for flood control strategies in case of similar floods in the future.

Occurrence and distribution of microplastics in surface sediments of a typical river with a highly eroded catchment, a case of the Yan River, a tributary of the Yellow River

Investigation of microplastic contamination in riverbed sediments can help clarify long-term microplastic pollution and establish prevention measures in watersheds. However, little research has been conducted on riverbed sediment pollution on the Loess Plateau, a highly eroded area in Northwest China. This research investigates the Yan River as a case study. The occurrence and distribution of microplastics were surveyed and analyzed to explore the microplastic pollution in the riverbed of the Loess Plateau. Microplastics were found in all sediment samples, with an abundance of 208.89–686.67 items kg−1. Polypropylene and polyethylene were the main microplastic components identified using Fourier transform infrared spectrometry and imaging systems. Particles 0.5–1.0 mm in size accounted for 38.5 % of the total microplastics in this region. The main microplastic colors were black, white, and transparent, which accounted for 40.75 %, 20.75 %, and 20.38 % of the total microplastics, respectively. There was an increasing trend in the microplastic abundance in sediments in the downstream direction that accompanied the increase in population density from 55.31 persons km−2 upstream to 230.05 persons km−2 downstream. Microplastic pollution was related to the complex geographical, semiarid monsoon climate, elevation, grassland, per capita GDP, and anthropogenic factors in the Yan River basin. The erodible loess and high-intensity rainstorm promoted severe soil erosion, which caused microplastics absorbed in the soil to migrate to the river. Poorly managed solid wastes, such as agricultural mulch, plastic bottles, and other plastic products are also sources of microplastics in the riverbed. This study further clarifies microplastic pollution in typical rivers of highly erosive areas and provides useful information for basin management.

Forest fire mobilization and uptake of metals by biota temporarily exacerbates impacts of legacy mining

While wildfires are a natural occurrence and ecosystems have evolved with fire, a changing climate is extending the wildfire season increasing the number, size and severity of fires in the western United States. In 2018, wildfire consumed 30% more area in the Western United States than the average ten years prior, and 76% more area than the average twenty years ago. These recent wildfires have impacted communities in the southwestern Rocky Mountains. In 2018, the 416 Fire, burned over 21,000 ha of public and private lands in southwestern Colorado. The 416 Fire is uniquely located in a legacy mine region in Colorado. The fire occurred in the Animas River watershed, which was already recovering from impacts of the Gold King Mine release of 2015. Three years of water quality monitoring after the 416 Fire have demonstrated elevated total and dissolved metal concentrations downstream of the burn area in Hermosa Creek and the Animas River. Following high-intensity rainstorm events, concentrations of metals such as aluminum, cadmium, iron, lead, manganese and zinc were significantly higher compared to pre-fire conditions in the burned watershed, and several metals often exceeded water quality standards for aquatic life. Macroinvertebrate monitoring in the Animas River and the main fire-impacted tributary indicate substantially altered insect communities. Macroinvertebrate tissue samples, with high concentrations of aluminum, iron, lead and nickel provide evidence that metals observed in the water column of fire-impacted streams were transferred to the benthic communities. In contrast, algae tissue from below the fire did not have elevated metals. High sediment volumes with absorbed metals from mineral rich and mined hillsides were transported to the streams and their aquatic ecosystems after the fire. Results from this study highlight the post-fire mobilization of naturally occurring metals to streams that already experience elevated metals from legacy mines, and will help in development of mitigation efforts in downstream communities.

Comprehensive analysis and numerical simulation of a large debris flow in the Meilong catchment, China

On June 17, 2020, a large debris flow occurred in the Meilong catchment following a short-duration, high-intensity rainstorm. The debris flow was initiated by two shallow landsides upstream of the catchment and had a volume of approximately 7.7 × 105 m3. It blocked the river and then induced flooding, causing significant losses to the local residents. In this study, through a combination of field observation, image interpretation, and laboratory experiments, the initiation mechanism, erosion depth along the main channel, and deposition area of this debris flow were comprehensively analyzed. A sequentially integrated numerical model considering the rainfall interception by vegetation, infiltration, and runoff process was developed. Considering the spatial variations in the climatic, hydrological, and geotechnical parameters, the entire process of debris flow initiation, motion, entrainment, and deposition was simulated. The computational outcomes matched well with the field observation results. A combination of the proposed integrated model and spatially varying parameters can be used to effectively describe the debris flow characteristics in the initiation and propagation stages and provide significant insights into the physical processes involved in such hazards.

Debris-flow Indicator for an early warning system in the Aosta valley region

Aosta Valley, an Alpine region in north-western Italy, has an early warning system (EWS) that issues hydrogeological alerts based on hydrological modelling and rainfall thresholds that identify the possibility of shallow landslides being triggered in different areas of the region. The high headwater catchments are characterized by the presence of permafrost and glacial sediments, and they are frequently prone to debris flows. The summer debris flows are initiated by short-duration, high-intensity rainstorms, which are associated with high meteorological uncertainty; therefore, they are not always detected by the early warning system of shallow landslides. In this study, the hydro-meteorological and permafrost conditions related to the debris-flow events from 2013 to 2018 are investigated in order to determine the variables affecting the triggering of debris flows. Debris-Flow Indicator (DFI), an early warning system specific for debris flows, was developed using recorded air temperatures, thunderstorm alerts and forecast rainfall. Two alert levels of the DFI were defined by two thresholds (S1 and S2) of the freezing level determined from performance metrics. The performance of the DFI was then studied with a back-analysis from 2013 to 2019, using observed air temperatures and forecast rainfalls. This analysis showed that the experimental implementation of the DFI in the EWS of the Aosta Valley region resulted in detecting most of the events with some false alerts (for the lower threshold, S1) or detecting only major events, but without generating false alerts (for the higher threshold, S2). Consequently, the DFI can be applied for issuing debris-flow alerts for large areas in mountain regions based only on meteorological data and forecast.

Wildfires Alter Forest Watersheds and Threaten Drinking Water Quality.

Wildfires are a natural part of most forest ecosystems, but due to changing climatic and environmental conditions, they have become larger, more severe, and potentially more damaging. Forested watersheds vulnerable to wildfire serve as drinking water supplies for many urban and rural communities. The highly variable nature of wildfire behavior combined with spatially complex patterns in vegetation, landscape, and hydrologic factors create uncertainty surrounding the postfire effects on water supplies. Wildfires often cause dramatic changes in forest vegetation structure and soil conditions, and alter the watershed processes that control streamflow, soil erosion, nutrient export, and downstream water chemistry. The authors' work centers on field and laboratory studies to advance knowledge of postfire changes in soil and water chemical composition that influence drinking water treatment. High intensity postfire rainstorms typically increase runoff that erodes ash and soil from burned landscapes and dramatically elevates turbidity, nutrient, and dissolved organic carbon (DOC) levels in surface waters, which can cause short-term challenges for water providers. There is also growing evidence that water quality impacts can persist after high severity fires due to slow vegetative recovery, and nitrogen and DOC have remained elevated for 15 years following high severity fire. Low-moderate temperatures during wildfire may also influence water quality. Research by the authors showed that the solubility of organic matter, and C and N released from soils increased following soil heating at temperatures ≤ 350 °C. Further, the water extracted organic matter from soils heated at 225-350 °C included higher proportions of condensed aromatic structures, such as black carbon and black nitrogen. Short-term postfire water quality degradation following high intensity rainstorms can force water treatment plants to shut down or can significantly challenge treatment process performance. Extreme turbidity and high DOC in poststorm water, coupled with compositional organic matter changes, reduced the coagulation efficiency of postfire water supplies. Field and lab-based studies documented the formation of small, aromatic soluble compounds during wildfire that contribute to inefficient DOC removal from postfire stormwater. Due to increased postfire DOC concentrations, and poor treatability of poststorm runoff, toxic disinfection byproduct (DBP) formation increased during water treatment. Exceedance of drinking water standards for the carbonaceous DBPs, trihalomethanes and haloacetic acids, may present a critical management concern for water providers following wildfires. Further, postfire formation of nitrogen compounds and increased nitrogenous DBP precursors for haloacetonitriles and chloropicrin were discovered. N-DBPs pose a public health concern due to their toxicity, and water providers should be aware of potential increases in N-DBP formation following fire. Evidence from the authors' studies demonstrates that even partially burned watersheds and wildfires burning at moderate temperature can have significant, lasting effects on C and N exports, source water quality, drinking water treatability, and DBP formation. Both short- and long-term postfire water quality impacts can create challenges for drinking water providers as they confront variability in supply and treatability. Communities, forest managers, and potable water providers will need to adapt to more frequent, destructive wildfires and anticipate greater variability in water quality.

Parameterization for EROSION-3D Model under Simulated Rainfall Conditions in Lower Shivaliks of India

The Shivalik foothills of northwestern India are very prone to soil erosion by water due to undulating slopes, highly erodible soils and high intensity rainstorm events during monsoon season. Physically based soil erosion modeling is seen as viable method for planning of measurements to reduce damages done by soil erosion. Nevertheless, parametrization of such models is a major challenge for large inaccessible areas. Several methods do exist for the estimation of the input parameters skin factor, surface roughness and resistance to erosion for the physically based soil erosion model EROSION-3D. Four rainfall experiments, each including dry and wet run, were conducted on different land use conditions on a research farm of the Regional Research Station Ballowal Saunkhri to test estimation methods. Modeling parameters were determined from these experiments. Parameter estimation by two methods for experimental conditions produced values in close range to experimentally determined values for resistance to erosion and surface roughness. Therefore, existing estimation methods are considered to be applicable for the conditions of the Shivalik mountains, except for skin factor. A first modeling with EROSION-3D using preliminary data of a small example catchment shows uncertainties resulting from range of determined and estimated soil parameters.

Weed seed dispersal via runoff water and eroded soil

High rainfall intensities on slopes produce runoff and erosion, but seeds are also carried down slope into streams by surface wash, causing weed infestation in lower parts of a river system. The study area was a cultivated valley (Houay Pano, Laos) farmed by smallholders and equipped with eight gauging stations: one draining the main catchment (60 ha) seven draining subcatchments (20–0.6 ha). All stations were used for sediment sampling, then sediments were scrutinized for seeds. The sampling took place simultaneously during, and immediately after, a single high intensity rainstorm. The event produced a total discharge of 1374 m3 measured at the outlet of the main catchment, in this water 4600 Mg suspended soil left the catchment together with approximately 1.34 million floating and suspended seeds. The rainstorm produced 2227 Mg of stream sediments (bedload), containing about 103,300 viable seeds. In total 131 species were identified, most seeds were weeds. The catchments were mostly covered by vegetation (fallow and forest) just 13% was cultivated, unprotected soil. Only unprotected soil produced runoff and erosion, whereas well-protected soil was subject to high seed loss. Seed dispersal without soil erosion occurred because the discharge needed to transport light-weight seeds is less than the force necessary to move soil particles. An enrichment factor of 85 was calculated, comparing number of seeds in running water leaving a field (20 seeds m−3) with seeds in stream water (1706 seeds m−3). Upper slope sites, when cultivated, yielded not only locally eroded seeds, but seed enrichment took place in running water on the way down to the stream, even under dense cover where no soil erosion occurred. As long as the drainage channels on the lower slopes are not fully recovered, any cultivation of uphill sites will re-open the old gullies and the mass of seeds accumulated in the channels will be re-mobilized and delivered directly into the stream. Our experiment demonstrates that the effect of preferential erosion of seeds, i.e. dispersal without erosion, is far greater than dispersal in sediments, making hill slope processes the major contributor to seed dispersal, while the trapping of seeds in wetlands and by the riparian area was only locally important.

Effect of inlet modelling on surface drainage in coupled urban flood simulation

For a highly developed urban area with complete drainage systems, flood simulation is necessary for describing the flow dynamics from rainfall, to surface runoff, and to sewer flow. In this study, a coupled flood model based on diffusion wave equations was proposed to simulate one-dimensional sewer flow and two-dimensional overland flow simultaneously. The overland flow model provides details on the rainfall-runoff process to estimate the excess runoff that enters the sewer system through street inlets for sewer flow routing. Three types of inlet modelling are considered in this study, including the manhole-based approach that ignores the street inlets by draining surface water directly into manholes, the inlet-manhole approach that drains surface water into manholes that are each connected to multiple inlets, and the inlet-node approach that drains surface water into sewer nodes that are connected to individual inlets. The simulation results were compared with a high-intensity rainstorm event that occurred in 2015 in Taipei City. In the verification of the maximum flood extent, the two approaches that considered street inlets performed considerably better than that without street inlets. When considering the aforementioned models in terms of temporal flood variation, using manholes as receivers leads to an overall inefficient draining of the surface water either by the manhole-based approach or by the inlet-manhole approach. Using the inlet-node approach is more reasonable than using the inlet-manhole approach because the inlet-node approach greatly reduces the fluctuation of the sewer water level. The inlet-node approach is more efficient in draining surface water by reducing flood volume by 13% compared with the inlet-manhole approach and by 41% compared with the manhole-based approach. The results show that inlet modeling has a strong influence on drainage efficiency in coupled flood simulation.

Biochar effects on soil water infiltration and erosion under seal formation conditions: rainfall simulation experiment

Soil amendment with biochar can result in decreased bulk density and soil penetration resistance, and increased water-holding capacity. We hypothesized that adding biochar could moderate the reductions in infiltration rates (IR) that occur during high-intensity rainstorms in seal-prone soils, and hence result in reduced runoff and erosion rates. The objectives were to (i) evaluate biochar potential to improve infiltration and control soil erosion, and (ii) investigate the mechanisms by which biochar influences infiltration rate and soil loss. Rainfall simulation experiments were conducted on two physicochemically contrasting, agriculturally significant, erosion-prone soils of Israel that are candidates for biochar amendment: (i) non-calcareous loamy sand, and (ii) calcareous loam. Biochar produced from mixed wood sievings from wood chip production at a highest treatment temperature of 620 °C was used as the amendment at concentrations from 0 to 2 wt%. In the non-calcareous loamy sand, 2 % biochar was found to significantly increase final IR (FIR) by 1.7 times, and significantly reduce soil loss by 3.6 times, compared with the 0 % biochar control. These effects persisted throughout a second rainfall simulation, and were attributed to an increase in soil solution Ca and decrease in Na, and a subsequently decreased sodium adsorption ratio (SAR). In the calcareous loam, biochar addition had no significant effect on FIR but did reduce soil loss by 1.3 times. There were no biochar-related chemical changes in the soil solution of the calcareous loam, which corresponds to the lack of biochar impact on FIR. Surface roughness of the calcareous loam increased as a result of accumulation of coarse biochar particles, which is consistent with decreased soil loss. These results confirm that biochar addition may be a tool for soil conservation in arid and semi-arid zone soils.

Block Slides on Extremely Weak Tectonic Clay Seams in Openly Folded Tertiary Mud-Rocks at Auckland and the Rangitikei Valley, North Island, New Zealand

Block slides have developed on extremely weak, thin clay seams of tectonic origin, parallel to bedding in gently dipping sandstones and mudstones of Tertiary age. Two areas of noted instability are investigated at Auckland and the Rangitikei valley. Dimensions range from 100 m across × 100 m long for short displacement block slides up to 4 km across × 3 km long for large landslide complexes in which block slides are a major component. Displacements of blocks range from incipient (cm) through short (30 m) to 2 or 3 km for large slides. Many of the Auckland slides are dormant but likely to move in a 2000 year return period earthquake or 100 year high intensity rain storm. At Rangitikei there are many active, younger slides. Sliding rates for active failures vary from a few cm/year to 50 m in 30 min. Host rocks are weak to very weak clayey sandstones and sandy mudstones. The seams are rich in smectite. They have polished and crushed walls, may have slickensides and some contain rounded rock fragments. Laboratory shear strength of the seams is 13 kPa cohesion and 13° friction, with a lower bound of 8° at zero cohesion. Strength is increased at the field scale by waviness, steps and splays. Continuity can be demonstrated over distances of hundreds of metres. Key investigation methods were mapping, shafts and trenches. Tectonic uplift, folding and faulting of the weak Tertiary strata and river down-cutting are perpetuating block slide development.

The role of precipitation type, intensity, and spatial distribution in source water quality after wildfire

Storms following wildfires are known to impair drinking water supplies in the southwestern United States, yet our understanding of the role of precipitation in post-wildfire water quality is far from complete. We quantitatively assessed water-quality impacts of different hydrologic events in the Colorado Front Range and found that for a three-year period, substantial hydrologic and geochemical responses downstream of a burned area were primarily driven by convective storms with a 30 min rainfall intensity >10 mm h−1. These storms, which typically occur several times each year in July–September, are often small in area, short-lived, and highly variable in intensity and geographic distribution. Thus, a rain gage network with high temporal resolution and spatial density, together with high-resolution stream sampling, are required to adequately characterize post-wildfire responses. We measured total suspended sediment, dissolved organic carbon (DOC), nitrate, and manganese concentrations that were 10–156 times higher downstream of a burned area compared to upstream during relatively common (50% annual exceedance probability) rainstorms, and water quality was sufficiently impaired to pose water-treatment concerns. Short-term water-quality impairment was driven primarily by increased surface runoff during higher intensity convective storms that caused erosion in the burned area and transport of sediment and chemical constituents to streams. Annual sediment yields downstream of the burned area were controlled by storm events and subsequent remobilization, whereas DOC yields were closely linked to annual runoff and thus were more dependent on interannual variation in spring runoff. Nitrate yields were highest in the third year post-wildfire. Results from this study quantitatively demonstrate that water quality can be altered for several years after wildfire. Because the southwestern US is prone to wildfires and high-intensity rain storms, the role of storms in post-wildfire water-quality impacts must be considered when assessing water-quality vulnerability.

Results and experiences gathered at the Rebaixader debris-flow monitoring site, Central Pyrenees, Spain

The wired and wireless monitoring system installed in the Rebaixader catchment detected six debris flows and 11 debris floods between 2009 and 2012. Apart from results directly related to the processes, many experiences associated with monitoring were collected. Debris flows and debris floods showed clear differences in both the recorded data and field observations. The distinction was especially visible in the stage measurements and the ground vibration registered by the most downstream geophone. At this geophone, a positive relation between the maximum ground vibration and the volume was also observed. The triggering of most events was associated with short, high-intensity rainstorms in summer, but some were also generated in spring, when the melting of snow cover and frozen soil played an additional role. A positive correlation between the volume and both the amount and the intensity of the triggering rainfall was observed. Regarding technical aspects, a switch between a “no-event” mode with a low sample rate and an “event” mode with a fast sampling was particularly useful at the station that register the passing of a flow. In addition, the stations, which most recently were installed at Rebaixader, apply wireless devices because wireless techniques include multiple advantages against standard wired systems. Although recorded data or even video images provide detailed information on the debris-flow behavior, we strongly recommend periodic field surveys along the entire torrent to verify and improve the interpretation obtained from the monitoring system.

Radioactive cesium isotope ratios as a tool for determining dispersal and re-dispersal mechanisms downwind from the Nevada Nuclear Security Site

Fractionation of the two longer-lived radioactive cesium isotopes (135Cs and 137Cs) produced by above ground nuclear tests have been measured and used to clarify the dispersal mechanisms of cesium deposited in the area between the Nevada Nuclear Security Site and Lake Mead in the southwestern United States. Fractionation of these isotopes is due to the 135-decay chain requiring several days to completely decay to 135Cs, and the 137-decay chain less than one hour decay to 137Cs. Since the Cs precursors are gases, iodine and xenon, the 135Cs plume was deposited farther downwind than the 137Cs plume. Sediment core samples were obtained from the Las Vegas arm of Lake Mead, sub-sampled and analyzed for 135Cs/137Cs ratios by thermal ionization mass spectrometry. The layers proved to have nearly identical highly fractionated isotope ratios. This information is consistent with a model where the cesium was initially deposited onto the land area draining into Lake Mead and the composite from all of the above ground shots subsequently washed onto Lake Mead by high intensity rain and wind storms producing a layering of Cs activity, where each layer is a portion of the composite.

Increasing occurrence of high-intensity rainstorm events relevant for the generation of soil erosion in a temperate lowland region in Central Europe

Summary Rainfall times series with a high temporal resolution of 1 min for the Emscher–Lippe catchment area were analysed for trends in regard to erosion-relevant storm events with intensities larger than 0.3 mm/min (>20 mm/h) for the last 70 years using the Mann–Kendall test. The analysis data showed for all investigated stations an increase of rainstorm events with erosion-relevant rainfall intensities; the trend was more pronounced over the last 35 years and was shown to be statistical significant for a critical zone with rainfall characteristics of: intensity iRain = 0.3–0.7 mm/min, duration tRain = 2–10 min and depth hRain = 1–3 mm. The increase of rainstorm events over the last 35 years was more pronounced in the summer season (July–September), but increases were detected also in the other seasons. The high-intensity storm events occured only ca. 4–15 times/year; the estimated trend increases of up to 0.5 events/year could therefore result in a multiplication of the occurrence of these storm events within only a few decades. This study has shown for the first time that the rainfall regime for temperate lowland regions in Germany has changed within its erosion-relevant spectrum over the last couple of decades. Parallel to the changes in the rainfall regime, increases in the annual and seasonal average temperature and changes in the occurrence of circulation patterns responsible for the generation of high-intensity storms were found, however not in the occurrence of thunderstorms. A climate-change driven increase of rain storm events over the last couple of decades and a potential future continuation of this trend may have several adverse effects for the study area and potentially for a larger region in Central Europe, for example an increase of soil erosion on slopes, the depletion of soil nutrients, an increased transport of nutrients and contaminants attached to sediment particles, their transfer into surface water bodies and consequential negative effects on stream habitats.

Slope Stability Problems in Central and Northern Jordan

Over the last four decades excessive hill-slope disturbances have been identified during highway construction and urban development in central and northern Jordan. Most of the major engineering projects were implemented on natural, steep slopes, related to old landslide complexes, weak geological structures, and soft lithological units of low-shearing resistance. Thus a wide range of landslides was reactivated, causing serious damage to highways and urban areas. Engineering activities often took place without previous appreciation of the geological, geomorphological, and hydrological setting. The human impact of the increased probability of landslides was also ignored. The final triggering factor responsible for these slope failures was the build-up in the materials of high pore-water pressures, caused by recurrent, high-intensity rainstorms. Geomorphological stability evaluation was carried out along the Amman-Jerusalem and Amman-Irbid highways and in the greater Amman area. It is concluded that hill-slo...