Low-intensity Rainfall Research Articles

Runoff at contrasting scales in a semiarid ecosystem: A complex balance between biological soil crust features and rainfall characteristics

Runoff in arid and semiarid areas is characterized by high spatial and temporal variability. The spatial component is largely associated with the high spatial heterogeneity of soil surface attributes, such as vegetation and rock fragment covers, topography, and soil crust typology. Biological soil crusts (BSCs) are a common soil cover in arid and semiarid areas, and they play an essential role in local hydrological processes, since they affect many soil surface attributes associated with hydrologic properties. Although several publications have reported on the influence of BSCs on runoff at microplot spatial scales, only a few have examined their influence on larger spatial scales. Moreover, very few studies have analyzed the effect of BSCs on runoff under natural rain conditions. This is difficult, since a complex pattern of interactions among rainfall properties, BSC characteristics and some local characteristics, such as topography or type of soil is expected. In addition, in order to achieve a realistic model of how BSCs and rainfall affect runoff, it would be necessary to consider the level of human-driven degradation of BSCs. In this study, runoff was analyzed in plots with varying cover of cyanobacterial and lichen BSCs at microplot and small hillslope scales for two hydrological years in badlands in SE Spain. Structural equation modelling (SEM) was applied to test both direct and indirect relationships of BSC cover, slope gradient, rainfall characteristics and runoff. Our model showed that rainfall characteristics were the main factors controlling runoff yield. The slope positively affected runoff at small hillslope scales, but did not influence runoff at microplot scales. Runoff decreased at both scales with increased lichen-BSC cover. However, this effect was only significant during low-intensity events. Under high rainfall intensities, neither the BSC cover nor the slope had a causal effect on runoff. Our results suggest that incorporation of BSC-crusted surfaces in models should improve their capabilities for low-intensity rainfall events in semiarid areas similar to ours, but would be less important for high-intensity events. In addition, our approach, which takes direct and indirect relationships of factors affecting runoff into consideration, provides a very accurate picture of the process.

Influence of rock fragment coverage on soil erosion and hydrological response: Laboratory flume experiments and modeling

Two laboratory flume experiments on the effect of surface rock fragments on precipitation‐driven soil erosion yields were carried out. The total sediment concentration, the concentration of seven individual size classes, and the flow discharge were measured. Digital terrain models (DTMs) were generated before and after one of the experiments. The results revealed that the rock fragments protected the soils from raindrop detachment and retarded the overland flow, therefore decreasing its sediment transport capacity. Rock fragments were found to affect selectively the different size classes in a manner that changed according to the time scale. For short times, the rock fragment coverage reduced erosion of the finer particles (<20 μm). For the midsize classes the protection decreased, while erosion of the larger size classes (>100 μm) was unaffected. At long times the rock fragment cover decreased the concentration of the individual size classes in proportion to effective rainfall intensity and the area exposed to raindrops. An area‐based modification of the Hairsine and Rose (H‐R) soil erosion model was employed to analyze the experimental data. The H‐R model predictions agreed well with the measured sediment concentrations when high rainfall intensity and low rock fragment cover were used. Predictions were instead less accurate with low rainfall intensity and high rock fragment cover. The DTM results showed that the presence of rock fragments on the soil surface led to increased soil compaction, perhaps due to higher soil moisture content (from greater infiltration) within the rock fragment‐covered flumes.

Effects of rock fragment cover on hydrological response and soil loss from Regosols in a semi-humid environment in South-West China

Controlling soil hydrological processes and combating soil erosion on agricultural fields are high priorities for crop production and ecological environments. In this research, the effect of land application of rock fragments on surface runoff, subsurface runoff, infiltration and soil loss on Regosols had been investigated under field conditions using a portable rainfall simulator. Experimental twin-plot (two subplot with 1-m wide by 2-m long, 32% slope) with different rock fragment covers ranging from 0–40% were exposed to three rainfall intensities, low (57±2mmh-1), medium (91±3mmh-1), and high (122±5mmh-1). Fifteen treatments were conducted in the experiments in duplicates. Surface runoff, subsurface runoff, soil moisture and sediment were measured. Results show that surface rock fragment cover retarded surface runoff, increased infiltration and subsurface runoff, and diminished sediment concentration and soil loss. The final infiltration rates, which increased with increasing rock fragment covers, were 16.5–42.7mmh-1 at low intensity, 19.7–50.8mmh-1 at medium intensity and 23.8–56.4mmh-1 at high intensity. Compared with bare soils, surface runoff rates were reduced to 24%, 51% and 64% in soils with 40% rock fragment cover at low, medium and high intensity rainfall, respectively. Subsurface runoff volume was significantly higher and time to start subsurface runoff was shorter as surface rock fragment cover increased. Compared with bare soils, subsurface runoff coefficients increased to 3.5, 3.3 and 2.9 times in soils with 40% rock fragment cover at low, medium and high intensity, respectively. Sediment concentrations increased from 9.8gL-1 for 40% rock fragment cover under high intensity rainfall to 51.5gL-1 for bare soils with rain falling at high intensity. The erosion rate was <12gm-2min-1 for soils with 40% rock fragment cover, even when rainfall intensity was high, while it was >15gm-2min-1 for bare soils under low intensity. The relationship between rock fragment cover and soil loss ratio can be expressed by an exponential function with a high degree of reliability, regardless of rainfall intensities. Overall, results indicate the surface rock fragments can be influential in shaping hydrological processes and soil loss from sloping farmland.

Use of Two Industrial Wastes as Soil Amendments: Effect on Dissolved Reactive Phosphorus in Runoff

To control the dissolved reactive phosphorus (DRP) concentration in a soil solution, a number of soil amendments were tested. In the current study, Blast Furnace Slag (BFS) and Water Treatment Residues (WTR) were tested on bare soil under two rainfall intensities and two soil roughness levels. The soil was fertilized with P (KH2PO4) at a rate of 400 kg ha−1 while BFS and WTR were applied at a rate of 5 g per 100 g of soil. Two soil roughness levels were exposed to artificial rainfall intensities of 30 and 65 mm h−1. Three rainfall events were performed on each treatment. The runoff water generated over an area of 0.5 m2 with a slope of 8% was collected at different time intervals and analyzed for DRP, Al, Fe, and K concentrations. The results showed that, regardless of rainfall intensity and soil roughness, the concentration of DRP in the runoff water increased with increasing runoff time from the unamended plots. However, in the BFS- and WTR-amended soils, the DRP concentration decreased with runoff time. Dissolved reactive P and DRP loads were the lowest from the WTR-amended plots, followed by the control and the BFS treatment plots. Water treatment residues reduced the mean DRP concentration by 27.3% and the DRP load by 32% compared to unamended plots. The two rainfall intensities significantly affected the DRP concentration and load. Under the low rainfall intensity, the DRP concentration and load were higher compared to the high rainfall intensity. The overall DRP concentration was not affected by changes in soil roughness. However, the DRP loads were higher from the plots with low soil roughness levels, especially during the first and second runs. Both the BFS and WTR were also effective in reducing the DRP concentrations in the drain water collected during the runoff events. The concentrations of Al, Fe, and K in the runoff water were not affected by the soil amendments. However, the electrical conductivity and pH readings were higher from the BFS-amended plots.

Assessment of the Regional Climate Model Version 3 over the Maritime Continent Using Different Cumulus Parameterization and Land Surface Schemes

Abstract This paper describes an assessment of the Regional Climate Model, version 3 (RegCM3), coupled to two land surface schemes: the Biosphere–Atmosphere Transfer System, version 1e (BATS1e), and the Integrated Biosphere Simulator (IBIS). The model’s performance in simulating precipitation over the Maritime Continent was evaluated against the 3-hourly Tropical Rainfall Measuring Mission (TRMM) Multisatellite Precipitation Analysis 3B42 product. It is found that the model suffers from three major errors in reproducing the observed rainfall histogram: underestimation of the frequency of dry periods, overestimation of the frequency of low-intensity rainfall, and underestimation of the frequency of high-intensity rainfall. Additionally, the model does not accurately reproduce the observed timing of the diurnal rainfall peak, particularly over land. These four errors persisted regardless of the choice of lateral boundary conditions, convective parameterization scheme, or land surface scheme. The magnitude of the wet–dry bias in the simulated volumes of rainfall was, however, strongly dependent on the choice of the convection scheme and lateral boundary conditions. The Grell convection scheme with Fritsch–Chappell closure was the best performing of the convection schemes, having the smallest error magnitudes in both the rainfall histogram and average diurnal cycle, and also having good representation of the land surface energy and evapotranspiration components. The 40-yr ECMWF Re-Analysis (ERA-40) was found to produce better simulations of observed rainfall when used as lateral boundary conditions than did the NCEP–NCAR reanalysis. Discussion of the nature of the major model errors is provided, along with some suggestions for improvement.

PENGARUH LAMA PERIODE KERING DAN INTENSITAS CURAH HUJAN TERHADAP PENETASAN BELALANG KEMBARA (LOCUSTA MIGRATORIA MANILENSIS MEYEN)

Effect of Dry Period and Rainfall Intensity on Emergence of the Migratory Locust (Locusta migratoria manilensis Meyen). Dry period and rainfall intensity were simulated experimentally to determine their effects on nymph emergence of the migratory locust (Locusta migratoria manilensis Meyen) (Orthoptera: Acrididae). The experiment was conducted in a factorial set up with two factors, i.e. dry periods (1, 2, 4, 8, and 12 week interval of watering) and rainfall intensity (80, 140, 200, and 260 mm/month). Locust nymphal emergence and time required to emerge after the watering were recorded and analyzed. Results of the experiment indicated that dry periods and rainfall levels affected nymphal emergence of the migratory locust. Interaction between dry periods and rainfall levels, however, were statistically not significant (F-value = 0,69 and P-value = 0,7526). Nymphal emergences of L. m. manilensis tended to be higher on soils that were watered less frequently. Similarly, locust emergences were also higher for the soil with lower rainfall intensity (received less amount of watering). At the 80 mm/month rainfall level, 20 – 105,5 days period (egg incubation period) were required before the locust emergence. Incubation period of the eggs was significantly higher as the breeding media (soil) were watered less frequently. On the other hand, time required for the egg to emerge as nymphs was relatively similar regardless of the dry period levels. All eggs emerged 14 – 15,5 days after watering.

Impact of Seasonality on Artificial Drainage Discharge under Temperate Climate Conditions

AbstractArtificial drainage systems affect all components of the water and matter balance. For the proper simulation of water and solute fluxes, information is needed about artificial drainage discharge rates and their response times. However, there is relatively little information available about the response of artificial drainage systems to precipitation. To address this need, we analysed 11 datasets from artificial drainage study sites (daily or hourly resolution), one daily dataset from an open ditch system, and three datasets from rainfall simulations on tile‐drained fields.When we considered all 11 artificial drainage study sites, we found that artificial drainage discharge responded to 70% of all rainfall events during the year, and that the response rate differed significantly between 56% summer and 84% in winter. A median of 23% of the yearly precipitation rate is discharged by artificial drainage systems, varying from 9% of the precipitation in summer to 54% of the precipitation in winter. The artificial drainage systems usually started to respond within the first hour under rain fed conditions, and the response time increased at lower rainfall intensities (&lt; 1 mm h–1). The peak outflow normally occurred within the first two days. The influence of soil texture and land use on artificial drainage discharge rates could not be reproduced properly, due to the spatial high variability caused by other site‐specific properties. (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Soil thickness effect on hydrological and erosion characteristics under sloping lands: A hydropedological perspective

Soil thickness exerts a first-order control on the hydrological processes of the hillslopes. However, from a hydropedological perspective, the knowledge of soil thickness effect on hydrological and erosion characteristics under sloping lands is limited. Based on a comprehensive survey of an experimental watershed in the Three Gorges Area of China, five typical sloping land plots (2 m × 1 m) with different soil thickness were selected along a hillslope to investigate their hydrological processes and erosion response under three rainfall intensities (60, 90 and 120 mm h −1) using a portable rainfall simulator. The results can be summarized as follows: (1) The surface flow coefficient was increased with increasing soil thickness, especially under the event of 60 mm h −1. (2) The subsurface flow of the 23, 31 and 45 cm plots mainly took the form of preferential flow. Conversely, the 59 and 76 cm plots mainly took the form of matrix flow. (3) A prolonged low intensity rainfall is much more likely to facilitate deep percolation and subsurface flow than a short high intensity rainfall regardless of soil thickness. (4) Soil thickness and rock fragment cover were the most important factors than other soil properties in determining the hydrological and erosion behaviors. Thin soils showed higher infiltration capacity than thick soils due to their more distinct hydrological processes of subsurface flow and deep percolation. Rock fragment cover enhanced infiltration and served as a shield to protect the soil surface from detaching. Due to the synergies between thin soil thickness and high rock fragment cover, thin soils displayed significantly lower erosion rates than thick soils in all rainfall events, which increased from 211 g m −2 h −1 for the 23 cm plot with rainfall of 60 mm h −1 to 4220 g m −2 h −1 for the 76 cm plot with rainfall of 120 mm h −1. Our study suggested that the emerging interdisciplinary field of hydropedology promotes synergistic integration of pedology (e.g. watershed scale soil thickness investigation and soil profile description) and hydrology (e.g. rainfall simulation, subsurface flow and deep percolation) to enhance the holistic study of soil–water interactions in the sloping lands with different soil thickness.

Runoff and soil erosion from highway construction spoil deposits: A rainfall simulation study

To measure soil loss from these road construction spoils, 30 rainfall simulations involving five rainfall intensities were conducted to study runoff and soil erosion processes on a road in China. Twenty-five of the rainfall simulations were carried out on loose materials five different slopes. Another five rainfall simulations were conducted on compacted road materials with a slope of 30.6%. The results show that soil bulk density has a positive effect on runoff rate, and the effect of slope on runoff rate changes with rainfall intensity. Higher soil bulk density increases soil loss under low rainfall intensity, but decreases soil loss when rainfall intensity is high. Soil loss is positively related to slope, but the relationship differs from that in prior studied of croplands and disturbed lands. Equations for predicting soil erosion from loose materials and compacted road are developed.

The Sensitivity of Northern Groundwater Recharge to Climate Change: A Case Study in Northwest Alaska1

Clilverd, Hannah M., Daniel M. White, Amy C. Tidwell, and Michael A. Rawlins, 2011. The Sensitivity of Northern Groundwater Recharge to Climate Change: A Case Study in Northwest Alaska. Journal of the American Water Resources Association (JAWRA) 47(6):1228–1240. DOI: 10.1111/j.1752-1688.2011.00569.x Abstract: The potential impacts of climate change on northern groundwater supplies were examined at a fractured-marble mountain aquifer near Nome, Alaska. Well water surface elevations (WSE) were monitored from 2004-2009 and analyzed with local meteorological data. Future aquifer response was simulated with the Pan-Arctic Water Balance Model (PWBM) using forcings (air temperature and precipitation) derived from fifth-generation European Centre Hamburg Model (ECHAM5) global circulation model climate scenarios for extreme and modest increases in greenhouse gases. We observed changes in WSE due to the onset of spring snowmelt, low intensity and high intensity rainfall events, and aquifer head recession during the winter freeze period. Observed WSE and snow depth compared well with PWBM-simulated groundwater recharge and snow storage. Using ECHAM5-simulated increases in mean annual temperature of 4-8°C by 2099, the PWBM predicted that by 2099 later freeze-up and earlier snowmelt will decrease seasonal snow cover by one to two months. Annual evapotranspiration and precipitation are predicted to increase 27-40% (55-81 mm) and 33-42% (81-102 mm), respectively, with the proportion of snowfall in annual precipitation decreasing on average 9-25% (p < 0.05). The amount of snowmelt is not predicted to change significantly by 2099; however, a decreasing trend is evident from 2060 in the extreme ECHAM5 greenhouse gas scenario. Increases in effective precipitation were predicted to be great enough to sustain sufficient groundwater recharge.

Erosion Characteristics Based on GIS and Fractal Dimensions

Soil erosion processes and erosion distribution was research focus to establish distributed mathematical equation in the soil erosion areas, GIS techniques and fractal theory provide a means to advance these studies.Slope erosion patterns of bare slope was studied under rainfall intensities of 45、90 and 130mm/h with 20°slope gradient using simulated rainfall experiment. The results showed that the time of rill appeared of lower rainfall intensity was later than that of high rainfall intensity；Within the rainfall time，the rill scale expanded increased with the increasing of rainfall intensity; The erosion distribution was studied by the three-dimensional laser scanner，The trend of rill erosion deep kept roughly consistent with that of sediment; The characteristics was analyzed of slope erosion by GIS, the fractal dimension and sediment were both increased with rainfall intensity, The fractal dimension was increasing with erosion pattern complexity. So the fractal dimension is the representative of erosion complexity.

Impact of urbanization on flooding: The Thirusoolam sub watershed – A case study

► The impact of urbanization due to change in land use pattern for Thirusoolam sub watershed is examined. ► Information is provided for better land use planning and control considering flood risk areas. ► Appropriate Manning’s coefficient and flow contribution from the upstream areas are taken into consideration. ► Rapid urbanization has increased the flooded area and water depth for the same amount of rainfall. The change in the land use pattern due to rapid urbanization adversely affects the hydrological processes in a catchment, leading to a deteriorating water environment. The increase in impervious areas disrupts the natural water balance. Reduced infiltration increases runoff and leads to higher flood peaks and volumes even for short duration low intensity rainfall. Due to their destructive effects, floods can significantly increase the expenses on mitigation efforts. The present study focuses on the Thirusoolam sub watershed, an urban watershed in Chennai. Land use changes associated with urbanization in the watershed are invariably reflected in the stream flow regime. This paper emphasizes on an integrated approach to flood management, considering the land use change into the hydrological model. Integrated Flood Management (IFM) aims to harmonize human activities and flood risks through appropriate interventions to modify the water regime, and adaptation of human behavior thereby reducing such risks. Therefore, the hydrological impacts of urbanization should be considered for effective urban planning. The outcome of the study would help in formulating policy guidelines and intervention strategies.

포도밭에 대한 비점오염원 유출특성 해석

This study analyzed the characteristics of stormwater runoff by rainfall type in orchard areas for two years. Effluents were monitored to calculate the EMCs and runoff loads of each pollutant. The runoff characteristics for nonpoint sources from vineyards were also inspected based on independent variables that affect runoff such as rainfall and rainfall intensity. The average runoff loads of each pollutant from vineyard_A and vineyard_B were found as follows: BOD 39.13 ㎎/㎡, COD 112.13 ㎎/㎡, TOC 54.98 ㎎/㎡, SS 1,681.8 ㎎/㎡, TN 18.29 ㎎/㎡, and TP 4.06 ㎎/㎡, which indicates that the COD's runoff load was especially high. The average EMCs from vineyard_A and vineyard_B, which represents the quality of rainfall effluent, were also analyzed: BOD 3.5 ㎎/L, COD 11.5 ㎎/L, TOC 5.2 ㎎/L, SS 211.7 ㎎/L, TN 1.774 ㎎/L, and TP 0.324 ㎎ /L. This suggested that the COD, as an indicator of organic pollutants, is high in terms of EMCs as well. As rainfall increased, the EMCs of BOD, COD, TOC and SS kept turning upward. At a point, however, the high rainfall brought about dilution effects and began to push down the EMCs. Higher rainfall intensities led to the increase in the EMCs that displays the convergence of rainfall. Low rainfall intensities also raised pollutant concentrations, although the concentrations themselves were slightly different among pollutants.

Methodology for land use change scenario assessment for runoff impacts: A case study in a north-western European Loess belt region (Pays de Caux, France)

Changes of agricultural land use often induce changes in hydrological behavior of watersheds. Hence, effective information regarding runoff responses to future land use scenarios provides useful support for decision-making in land use planning and management. The objective of this study is to develop a methodology to assess land use change scenario impacts on runoff at the watershed scale. This objective implies translating qualitative information from scenarios into quantitative input parameters for biophysical models. To do so, qualitative information from scenarios should be quantified and spatialized. The approach is based on the combination of 2015 local land use change scenarios (SYSPHAMM method) based on local stakeholders expertise, a model of spatio-temporal allocation of crops to fields (LandSFACTS model) and a watershed runoff model (STREAM model). The study was conducted for regions underlain by silty loamy soils scattered across Northern Europe. It was applied on the Saussay watershed in Upper Normandy (France). The approach is illustrated through runoff assessment of one of the land use change scenarios (characterized by the ending of the set-aside obligation and the disappearance of dairy farming). This scenario appeared relevant for local stakeholders. The methodology presented suggests that assessing local land use scenarios in terms of runoff requires taking into account crop allocation diversity allowed by farmers' decision rules. This requirement accounts for runoff variability at the watershed outlet since crops spatial distribution throughout the watershed, depending on farmers' specific decision rules (i.e. cropping systems), strongly condition runoff phenomenon. Besides, choices regarding scenario implementation (quantification and spatialization) should to be made according to those cropping systems. Accordingly, taking into account crop allocation diversity due to farmers' cropping systems shows that there is a variability in terms of runoff at the watershed outlet (from 19 478 m3 to 35 004 m3 for the winter period and a low-intensity rainfall event for example). This variability can then be explored with local decision makers with the aim of finding solutions reducing runoff risks. The proposed approach provides a useful source of information for assessing the responses of surface runoff of future land use changes. Such scenarios providing impact assessment on runoff should encourage both local policy makers and local actors to actively discuss the future of land use in Upper Normandy.

Runoff estimation in southern Brazil based on Smith's modified model and the Curve Number method

► We model surface runoff for different soil classes and management system. ► Runoff can be estimated based on rainfall intensity , land slope and soil porosity . ► The Smith's modified model estimates runoff for no-tillage management system. ► Curve Number overestimates the cumulative runoff for no-tillage management system. The objective of this work was to measure and model the runoff for different soils classes at different rainfall intensities (30, 60 and 120 mm h −1 ) in Southern Brazil. A portable rainfall simulator with multiple nozzles was used to simulate these rainfall intensities. For each soil, the initial time and runoff rate, rainfall characteristics (total, duration and intensities), surface slope, crop residue amount and cover percentage, soil densities (bulk and particle), soil porosity (bulk, macro and micro), textural fractions (clay, silt and sand), and the initial and saturated soil water content were measured. The runoff measured was compared to Smith's modified and Curve Number (USDA-SCS) models. The cumulative runoff losses were 67, 45 and 27% of the total rainfall, for a Rhodic Paleudalf, Typic Quartzipsamment and Rhodic Hapludox, respectively. An inverse relationship was observed between initial runoff and the runoff rate, independently of the soil surface and rainfall conditions. Increasing rainfall intensity decreased the time to runoff and increased runoff rate. The Smith's modified model overestimated the cumulative runoff by about 4%. The Smith's modified model presented a better estimate for both higher and lower rainfall intensities (120 and 30 mm h −1 ). The SCS Curve Number model overestimated the cumulative runoff by about 34%. This large overestimate is probably due to that the model did not take into account the soil tillage system used in the field by farmers, particularly for irrigated conditions. The combination of high porosity, low bulk density and presence of crop residue on soil surface decreased runoff losses, independently of the soil texture class. Smith's modified model better estimated the surface runoff for soil with a high soil water content, and it was considered satisfactory for Southern Brazil runoff estimations. The SCS Curve Number model overestimated the cumulative runoff and its use needs adjustments particularly for no-tillage management system.

Impact of Manufactured Coal Ash Aggregates on Water Quality during Open Pit Restoration: 1. A Statistical Screening Test

Utilization of manufactured coal ash aggregates (MAs) as a subsoil substitute during restoration of an open pit was assessed in a three-factor, two-level factorial analysis. The factors of interest were the MA application rate (2:1 or 1:2 topsoil/MA volume ratio), rainfall intensity (high or low), and aggregate size (2.36–4.75 mm or 4.75–9.53 mm). Among the water quality parameters examined (pH, turbidity, heavy metal content (lead and cadmium), conductivity, and hardness), the last two parameters were significantly higher (p,0.05) in soil amended with MAs than in a control reactor using sand. A low rainfall intensity and larger aggregate size resulted in a lower water quality with regard to conductivity (7,12 mS/cm) and hardness (600,2000 mg/L as CaCO3) during the 63 day experiment. f 2011 The University of Kentucky Center for Applied Energy Research and the American Coal Ash Association All rights reserved. A R T I C L E I N F O Article history: Received 01 August 2010; Received in revised form 08 October 2010; Accepted 25 October 2010

Sediment budget monitoring of a debris-flow torrent (French Prealps)

ABSTRACT The Manival near Grenoble (French Prealps) is a very active debris-flow torrent equipped with a large sediment trap (25 000 m 3 ) protecting an urbanized al-luvial fan from debris-flows. We began monitoring the sediment budget of the catchment controlled by the trap in Spring 2009. Terrestrial laser scanner is used for monitoring topographic changes in a small gully, the main channel, and the sediment trap. In the main channel, 39 cross-sections are surveyed after every event. Three periods of intense geomorphic activ-ity are documented here. The first was induced by a convective storm in August 2009 which triggered a debris-flow that deposited ~1,800 m of sediment in the trap. The debris-flow originated in the upper reach of the main channel and our observations showed that sediment outputs were entirely supplied by channel scouring. Hillslope debris-flows were initiated on talus slopes, as revealed by terrestrial LiDAR resur-veys; however they were disconnected to the main channel. The second and third periods of geomorphic activity were induced by long duration and low inten-sity rainfall events in September and October 2009 which generate small flow events with intense bed-load transport. These events contribute to recharge the debris-flow channel with sediments by depositing important gravel dunes propagating from headwaters. The total recharge in the torrent subsequent to bedload transport events was estimated at 34% of the sediment erosion induced by the August debris-flow.

Aeration and gutter water levels in siphonic roof drainage systems

An investigation is presented into how negative system pressures, the degree of aeration, and gutter water levels are affected by the number of outlets in a siphonic roof drainage system. The experimental results show that system pressures decrease if outlets are blocked. It is also shown that the depth of water above an outlet is strongly influenced by the negative pressure acting at the outlet. As the suction effect at the outlet increases, due to lower system pressures, more water and air will be drawn into the outlets and this will result in a corresponding increase in overall gutter water depth. The results also show that there is often built-in redundancy in multiple outlet siphonic systems experiencing lower-intensity rainfall events, and if one or two outlets were blocked, the system would still operate satisfactorily. A new outlet suppressor was trialled and this was shown to reduce gutter water levels by up to 58% at some positions in the gutter. Il est présenté une enquête sur la manière dont les pressions négatives dans le système concerné, le degré d'aération et les niveaux d'eau dans les chéneaux sont affectés par le nombre d'orifices de sortie dans un système d'écoulement des eaux de toit par siphonnage. Les résultats expérimentaux montrent que les pressions dans le système diminuent si des orifices de sortie sont obturés. Il est également montré que la profondeur de l'eau au-dessus d'un orifice de sortie est fortement influencée par la pression négative s'exerçant à l'orifice de sortie. Plus l'effet de succion à l'orifice de sortie augmente, en raison des pressions plus faibles dans le système, et plus les quantités d'air et d'eau entraînées dans les orifices de sortie seront importantes, et cela aura pour résultat une augmentation correspondante de la profondeur générale de l'eau dans les chéneaux. Les résultats montrent également qu'il existe souvent une redondance intégrée dans les systèmes à siphons comportant des orifices de sortie multiples et soumis à des épisodes pluvieux de faible intensité, et que si un ou deux orifices de sortie sont obturés, le système fonctionne encore de manière satisfaisante. Un nouvel obturateur d'orifice de sortie a été essayé, ce qui a permis de montrer que celui-ci réduit dans une proportion allant jusqu'à 58 % en certains points les niveaux d'eau dans les chéneaux. Mots clés: aération, niveaux d'eau dans les chéneaux, pressions négatives, écoulement des eaux de toit par siphonnage

Simulation of the Diurnal Cycle in Tropical Rainfall and Circulation during Boreal Summer with a High-Resolution GCM

Abstract The simulation of the diurnal cycle (DC) of precipitation and surface wind pattern by a general circulation model (GCM) with a uniform horizontal resolution of 50 km over the global domain is evaluated. The model output is compared with observational counterparts based on datasets provided by the Tropical Rainfall Measuring Mission and reanalysis products of the European Centre for Medium-Range Weather Forecasts. The summertime diurnal characteristics over tropical regions in Asia, the Americas, and Africa are portrayed using the amplitude and phase of the first harmonic of the 24-h cycle, departures of data fields during selected hours from the daily mean, and differences between extreme phases of the DC. There is general agreement between the model and observations with respect to the large-scale land–sea contrasts in the DC. Maximum land precipitation, onshore flows, and landward migration of rainfall signals from the coasts occur in the afternoon, whereas peak maritime rainfall and offshore flows prevail in the morning. Seaward migration of precipitation is discernible over the western Bay of Bengal and South China Sea during nocturnal and morning hours. The evolution from low-intensity rainfall in the morning/early afternoon to heavier precipitation several hours later is also evident over selected continental sites. However, the observed incidence of rainfall with very high intensity in midafternoon is not reproduced in the model atmosphere. Although the model provides an adequate simulation of the daytime upslope and nighttime downslope winds in the vicinity of mountain ranges, valleys, and basins, there are notable discrepancies between model and observations in the DC of precipitation near some of these orographic features. The model does not reproduce the observed seaward migration of precipitation from the western coasts of Myanmar (Burma) and India, and from individual islands of the Indonesian Archipelago at nighttime.

Rainfall influence on plot-scale runoff and soil loss from repeated burning in a Mediterranean-shrub ecosystem, Valencia, Spain

The effect of a repeated burning on soil hydrology and erosive parameters was studied on a Mediterranean forest soil (Rendzic leptosol) with the aim of identifying the effects of the fire and climatic parameters related to the post-fire runoff and soil loss. The study was carried out in an Experimental Permanent Field Station (La Concordia), close to Valencia (Spain). This field station is located on a calcareous hillside facing SSE, and is composed of nine erosion plots (20 × 4 m). Firstly, experimental fires were performed in June 1995 with two fire treatments (T1 or high severity fire and T2 or moderate severity fire) and a control one (unburnt, T3). The repeated fire (low severity) was carried out in July 2003. The studied period was focused from 18 months before the repeated fire (July 2003) until 18 months after it. Rainfall characteristics of each single event were recorded, which allowed us to statistically distinguish four time periods according to the rainfall intensity and duration: periods I (March 2002 to May 2003) and III (December 2003 to early May 2004) with low intensity and long duration rainfalls, and periods II (June 2003 to November 2003) and IV (late May 2004 to December 2004) with high intensity and short duration rainfalls. Before the 2003 fire, the partial recovery of soil and vegetation from the previous burning in 1995 led to a diminution in the runoff rates (6.5 L m − 2 in burned plots and 1.8 L m − 2 in unburnt ones). Six months later (period II), runoff increased in one order of magnitude (23.9 L m − 2 in burnt plots and 1.1 L m − 2 in the unburnt ones) due, in part, to the short time elapsed from fire until high intensity rainfalls. These differences in runoff production were maintained during the whole post-fire period. Fire effects were reflected in the erosion rates. Soil losses prior to the 2003 fire, in both fire treatments and in the control one, were scant relative to post-fire levels. However, six months after the repeated fire (period II) and almost one year later (period IV), soil losses increased into two orders of magnitude coinciding with the post-fire bare soil augment. The repeated fire impact and rainfall intensity magnified runoff and soil loss. Significant linear relationships between rainfall intensity, runoff and soil loss, were obtained for the burned plots. In the burned areas, rain intensities increased to 20 mm h − 1 augmenting the runoff and soil loss in one and two orders of magnitude, respectively.