Spatial structures of stream and hillslope drainage networks following gully erosion after wildfire

The drainage networks of catchment areas burned by wildfire were analysed at several scales. The smallest scale (1–1000 m²) representative of hillslopes, and the small scale (1000 m² to 1 km²), representative of small catchments, were characterized by the analysis of field measurements. The large scale (1–1000 km²), representative of perennial stream networks, was derived from a 30‐m digital elevation model and analysed by computer analysis. Scaling laws used to describe large‐scale drainage networks could be extrapolated to the small scale but could not describe the smallest scale of drainage structures observed in the hillslope region. The hillslope drainage network appears to have a second‐order effect that reduces the number of order 1 and order 2 streams predicted by the large‐scale channel structure. This network comprises two spatial patterns of rills with width‐to‐depth ratios typically less than 10. One pattern is parallel rills draining nearly planar hillslope surfaces, and the other pattern is three to six converging rills draining the critical source area uphill from an order 1 channel head. The magnitude of this critical area depends on infiltration, hillslope roughness and critical shear stress for erosion of sediment, all of which can be substantially altered by wildfire. Order 1 and 2 streams were found to constitute the interface region, which is altered by a disturbance, like wildfire, from subtle unchannelized drainages in unburned catchments to incised drainages. These drainages are characterized by gullies also with width‐to‐depth ratios typically less than 10 in burned catchments. The regions (hillslope, interface and channel) had different drainage network structures to collect and transfer water and sediment. Copyright © 2005 John Wiley & Sons, Ltd.     

地震地磁场野外观测同步控制系统研制与应用

针对地震地磁野外观测的需求,开发研制了一种基于无线网络的野外同步观测系统。该系统主要由接口单元、采集控制(CPU)单元、无线单元、传输网络、计算机控制中心等组成。该系统操作简单,实用性强,具有远程唤醒及休眠、校时等服务功能,也可应用到地磁台阵的数据传输与同步工作中。     

Estimation of the normal geomagnetic field and geological interpretation of the normal field anomalies over middle-northern Croatia

Based on the ground survey of total-field magnetic data at 53 sites, which recorded a time-series over the interval 2003–2005, the core field + long wavelength lithospheric field over the middle-northern Croatia region was calculated. The area of the survey was 18900 km², an average distance between the neighbouring sites being 12 km. The results were reduced to 2004.5 epoch. This “normal” total-field was estimated using the firstorder Taylor polynomial as a function of geographic coordinates, and the polynomial coefficients were calculated with three methods of adjustment: simple and weighted least squares fits and adjustment according to the most frequent value. The stability of the normal field was tested using the Monte Carlo-type test, by decreasing the input data set in each adjustment (up to 90%). All obtained field residuals (measured-“normal”) were mutually compared, as well as fit coefficients of the Taylor polynomials. The residual values indicate the presence of shorter-wavelength anomalies, specifically three major residual anomalies were found (−106 nT, 74 nT and 57 nT). The geostatistical analysis of the ground survey data and the normal field residuals (respectively), using the median absolute deviation method, was further conducted in order to evaluate the calculated anomalies. The geological situation around the anomalies derived by the median absolute deviation method, and around the normal field residual anomalies, is given. The correlation was found between higher value anomalies of the normal field residuals, and shallow volcanic rocks and oil field, respectively.     

Combined discrete and continuous gravity observations at Mount Etna

Systematic investigation of discrete gravity measurements has continued at Mount Etna since 1986. The network now covers an area of 400 km² with about 70 stations 0.5–3 km apart. Mass redistributions occurring at depths ranging between about 8 km below sea level and a few hundred metres below the surface (magma level changes within the shallower parts of the feeding conduits) have been identified from these data. Conventional (discrete) microgravity monitoring on a network of stations furnishes only instantaneous states of the mass distribution at continuously active systems. In order to obtain information on the rate at which the volcanic processes (and thus mass transfers) occur, three stations for continuously recording gravity where installed on Mount Etna in 1998. A 16-month long sequence from one of the continuously running stations (PDN, located 2 km from the active northeast crater at the summit of Etna volcano) is presented. After removing the effects of Earth Tide and tilt, the correlation of the residual gravity sequence with simultaneous recordings of meteorological parameters acquired at the same station was analysed. Once the meteorological effects have also been removed, continuous gravity changes are within 10 μGal of gravity changes measured using conventional microgravity observations at sites very close to the continuous station. This example shows how discrete and continuous gravity observations can be used together at active volcanoes to get a fuller and more accurate picture of the spatial and temporal characteristics of volcanic processes.     

Double origin of hydrothermal convective flux variations in the Fossa of Vulcano (Italy)

Soil-temperature measurements can provide information on the distribution of degassing fissures, their relationship to the internal structure of the volcano, and the temporal evolution of the system. At Vulcano Island (Italy), heat flux from a <3 km-deep magma body drives a hydrothermal system which extends across the main Fossa crater. This heat flux is also associated with variable magmatic gas flow. A high-density map of soil-temperatures was made in 1996 at a constant depth of 30 cm on the central and southern inner flanks of the Fossa crater. These measurements extended over an area covering about 0.04 km², across which the heat flux is predominantly associated with a shallow boiling aquifer. The map shows that hot zones relate to structures of higher permeability, mainly associated with a fissure system dating from the last eruptive cycle (1888–1890). From 1996 to January 2005, we studied the evolution of the heat flux for the high temperature part of the map, both by repeating our measurements as part of 14 visits, during which temperatures were measured at a constant depth, and using data from permanent stations which allowed soil-temperatures to be continuously measured for selected vertical profiles. These data allowed us to calculate the heat flux, and its variation, with good precision for values lower than about 100 W m⁻², which is generally the case in the study area. Above 100 W m⁻², although the heat flux value is underestimated, its variations are recorded with an error less than 10%. During the period 1996–2004, two increases in the thermal flux were recorded. The first one was related to the seismic crisis of November 1998 which opened existing or new fissures. The second, in November 2004, was probably due to magma migration, and was associated with minor seismic activity.     

A critical zone observatory dedicated to suspended sediment transport: The meso-scale Galabre catchment (southern French Alps)

The 20 km² Galabre catchment belongs to the French network of critical zone observatories (OZCAR; Gaillardet et al., Vadose Zone Journal, 2018, 17(1), 1–24). It is representative of the sedimentary lithology and meteorological forcing found in Mediterranean and mountainous areas. Due to the presence of highly erodible and sloping badlands on various lithologies, the site was instrumented in 2007 to understand the dynamics of suspended sediments (SS) in such areas. Two meteorological stations including measurements of air temperature, wind speed and direction, air moisture, rainfall intensity, raindrop size and velocity distribution were installed both in the upper and lower part of the catchment. At the catchment outlet, a gauging station records the water level, temperature and turbidity (10 min time-step). Stream water samples are collected automatically to estimate SS concentration-turbidity relationships, allowing quantification of SS fluxes with known uncertainty. The sediment samples are further characterized by measuring their particle size distributions and by applying a low-cost sediment fingerprinting approach using spectrocolorimetric tracers. Thus, the contributions of badlands located on different lithologies to total SS flux are quantified at a high temporal resolution, providing the opportunity to better analyse the links between meteorological forcing variability and watershed hydrosedimentary response. The set of measurements was extended to the dissolved phase in 2017. Both stream water electrical conductivity and major ion concentrations are measured each week and every 3 h during storm events. This extension of measurements to the dissolved phase will allow progress in understanding both the origin of the water during the events and the partitioning between particulate and dissolved fluxes of solutes in the critical zone. All data sets are available at https://doi.osug.fr/public/DRAIXBLEONE_GAL/index.html .     

Does more mean less in epicentre estimation?

The epicentres of explosions at two test sites – Balapan (Shagan River), Former Soviet Union and Lop Nor, China – are estimated using the onset times of P from only three or four array stations at teleseismic distances. The epicentres of the explosions are known to within about 1 km from studies that make use of information from satellite imagery; these estimates are taken to be the true epicentres. With the true epicentres, differences between the true travel times and the times from travel-time tables are estimated. The differences include a component – path effects – that results in epicentre bias. Comparing our estimates using three or four stations with the true epicentres shows that with correction for path effects most of the epicentres are within 5 km of true and even without correction most estimated epicentres are within 10 km of true. The results confirm the conclusion of Evernden that if reading error in P times has a standard deviation of a few tenths of a second, reliable epicentres can be obtained given readings from only a few stations. This implies, what has been noted by others, that for epicentre estimation, better results can be obtained with a few well read P times from a constant network of the most reliable and sensitive stations, than by using uncritically all the available times. Even without correction for path effects none of the explosions (with times free from possible clock errors) falls outside a circular 1000 km² region; 1000 km² being the search area allowed for an on-site inspection under the Comprehensive Test Ban Treaty. The results suggest that rather than try and calibrate the whole of the International Monitoring System, being set up to verify the Test Ban, it would be better initially to concentrate on calibrating the few stations with the longest recording history and lowest detection thresholds.     

Development and application of a spatially‐distributed Arctic hydrological and thermal process model (ARHYTHM)

A process‐based, spatially distributed hydrological model was developed to quantitatively simulate the energy and mass transfer processes and their interactions within arctic regions (arctic hydrological and thermal model, ARHYTHM). The model first determines the flow direction in each element, the channel drainage network and the drainage area based upon the digital elevation data. Then it simulates various physical processes: including snow ablation, subsurface flow, overland flow and channel flow routing, soil thawing and evapotranspiration. The kinematic wave method is used for conducting overland flow and channel flow routing. The subsurface flow is simulated using the Darcian approach. The energy balance scheme was the primary approach used in energy‐related process simulations (snowmelt and evapotranspiration), although there are options to model snowmelt by the degree‐day method and evapotranspiration by the Priestley–Taylor equation. This hydrological model simulates the dynamic interactions of each of these processes and can predict spatially distributed snowmelt, soil moisture and evapotranspiration over a watershed at each time step as well as discharge in any specified channel(s). The model was applied to Imnavait watershed (about 2·2 km²) and the Upper Kuparuk River basin (about 146 km²) in northern Alaska. Simulated results of spatially distributed soil moisture content, discharge at gauging stations, snowpack ablations curves and other results yield reasonable agreement, both spatially and temporally, with available data sets such as SAR imagery‐generated soil moisture data and field measurements of snowpack ablation, and discharge data at selected points. The initial timing of simulated discharge does not compare well with the measured data during snowmelt periods mainly because the effect of snow damming on runoff was not considered in the model. Results from the application of this model demonstrate that spatially distributed models have the potential for improving our understanding of hydrology for certain settings. Finally, a critical component that led to the performance of this modelling is the coupling of the mass and energy processes. Copyright © 2000 John Wiley & Sons, Ltd.     

Use of microtremor measurement for assessing site effects in Northern Belgium – interpretation of the observed intensity during the MS = 5.0 June 11 1938 earthquake

To provide quantitative information on site effects in the northern part of Belgium, forty-seven H/V microtremor measurements were performed with 5 second seismometers over an area of about 15.000 km². Most of the results show a northward regular increase of the fundamental period in agreement with the augmentation of the Mesozoic and Cainozoic soft sedimentsthickness from a few meters 40 km south of Brussels to 900 m at the Netherlands-Belgium border. The measured resonance frequency values wereconsistent with theoretical computations performed at different sites onthe basis of existing information and shallow seismic experiments. At oneparticular site (Uccle) where borehole data were available, microtremor measurements using an array of four seismological stations with differentapertures allowed to obtain the low frequency part of the Rayleigh wave dispersion curve, extending the range covered by the analysis of surfacewaves artificially generated. The Vs profile derived from the surface waveinversion corroborates the 1 Hz natural frequency of the site. Comparison of these results with the macroseismic information concerning the M_S = 5.0 1938 earthquake which occurred 50 km west of Brussels,confirmed the hypothesis that the geological structure of the Brabant massifis likely to control damage distribution during such an earthquake. Comparisonbetween the intensity map of the 1938 earthquake and the resonance period ofsediments obtained by our microtremor study shows a clear relation betweenthe two parameters. During the 1938 earthquake, site effects played a prominent role due to the dimension of the source whose corner frequency wasabout 1 Hz.     

Spatial variability of rainfall on a sub‐kilometre scale

The variability of rainfall in space and time is an essential driver of many processes in nature but little is known about its extent on the sub‐kilometre scale, despite many agricultural and environmental experiments on this scale. A network of 13 tipping‐bucket rain gauges was operated on a 1·4 km² test site in southern Germany for four years to quantify spatial trends in rainfall depth, intensity, erosivity, and predicted runoff. The random measuring error ranged from 10% to 0·1% in case of 1 mm and 100 mm rainfall, respectively. The wind effects could be well described by the mean slope of the horizon at the stations. Except for one station, which was excluded from further analysis, the relative differences due to wind were in maximum ±5%. Gradients in rainfall depth representing the 1‐km² scale derived by linear regressions were much larger and ranged from 1·0 to 15·7 mm km^?1 with a mean of 4·2 mm km^?1 (median 3·3 mm km^?1). They mainly developed during short bursts of rain and thus gradients were even larger for rain intensities and caused a variation in rain erosivity of up to 255% for an individual event. The trends did not have a single primary direction and thus level out on the long term, but for short‐time periods or for single events the assumption of spatially uniform rainfall is invalid on the sub‐kilometre scale. The strength of the spatial trend increased with rain intensity. This has important implications for any hydrological or geomorphologic process sensitive to maximum rain intensities, especially when focusing on large, rare events. These sub‐kilometre scale differences are hence highly relevant for environmental processes acting on short‐time scales like flooding or erosion. They should be considered during establishing, validating and application of any event‐based runoff or erosion model. Copyright © 2009 John Wiley & Sons, Ltd.     

Long-term SMOS soil moisture products: A comprehensive evaluation across scales and methods in the Duero Basin (Spain)

The European Space Agency’s Soil Moisture and Ocean Salinity (SMOS) Level 2 soil moisture and the new L3 product from the Barcelona Expert Center (BEC) were validated from January 2010 to June 2014 using two in situ networks in Spain. The first network is the Soil Moisture Measurement Stations Network of the University of Salamanca (REMEDHUS), which has been extensively used for validating remotely sensed observations of soil moisture. REMEDHUS can be considered a small-scale network that covers a 1300 km² region. The second network is a large-scale network that covers the main part of the Duero Basin (65,000 km²). At an existing meteorological network in the Castilla y Leon region (Inforiego), soil moisture probes were installed in 2012 to provide data until 2014. Comparisons of the temporal series using different strategies (total average, land use, and soil type) as well as using the collocated data at each location were performed. Additionally, spatial correlations on each date were computed for specific days. Finally, an improved version of the Triple Collocation (TC) method, i.e., the Extended Triple Collocation (ETC), was used to compare satellite and in situ soil moisture estimates with outputs of the Soil Water Balance Model Green-Ampt (SWBM-GA). The results of this work showed that SMOS estimates were consistent with in situ measurements in the time series comparisons, with Pearson correlation coefficients (R) and an Agreement Index (AI) higher than 0.8 for the total average and the land-use averages and higher than 0.85 for the soil-texture averages. The results obtained at the Inforiego network showed slightly better results than REMEDHUS, which may be related to the larger scale of the former network. Moreover, the best results were obtained when all networks were jointly considered. In contrast, the spatial matching produced worse results for all the cases studied.These results showed that the recent reprocessing of the L2 products (v5.51) improved the accuracy of soil moisture retrievals such that they are now suitable for developing new L3 products, such as the presented in this work. Additionally, the validation based on comparisons between dense/sparse networks and satellite retrievals at a coarse resolution showed that temporal patterns in the soil moisture are better reproduced than spatial patterns.     

Post‐fire hydrological response and suspended sediment transport of a terraced Mediterranean catchment

In July 2013, a wildfire severely affected the western part of the island of Mallorca (Spain). During the first three post‐fire hydrological years, when the window of disturbance tends to be more open, the hydrological and sediment delivery processes and dynamics were assessed in a representative catchment intensively shaped by terracing that covered 37% of its surface area. A nested approach was applied with two gauging stations (covering 1.2 km² and 4.8 km²) built in September 2013 that took continuous measurements of rainfall, water and sediment yield. Average suspended sediment concentration (1503 mg L^?1) and the maximum peak (33 618 mg L^?1) were two orders of magnitude higher than those obtained in non‐burned terraced catchments of Mallorca. This factor may be related to changes in soils and the massive incorporation of ash into the suspended sediment flux during the most extreme post‐fire event; 50 mm of rainfall in 15 min, reaching an erosivity of 2886 MJ mm ha^?1 h^?1. Moreover, hysteretic counter‐clockwise loops were predominant (60%), probably related to the increased sensitivity of the landscape after wildfire perturbation. Though the study period was average in terms of total annual precipitation (even higher in intensities), minimal runoff (2%) and low sediment yield (6.3 t km^?2 y^?1) illustrated how the intrinsic characteristics of the catchment, i.e. calcareous soils, terraces and the application of post‐fire measures, limited the hydrosedimentary response despite the wildfire impact. Copyright © 2017 John Wiley & Sons, Ltd.     

Catchments of German surface water bodies

The European Water Framework Directive demands to assess and report the chemical and ecological status of water bodies (WB). Linking their status to drivers and pressures and deriving suitable mitigation measures require knowledge of the shape and area of WB catchments. We derived a network of 26 570 WB catchments in Germany using the hydrologically-defined drainage basins of the German federal states. We established a network of 338 149 drainage basins. This network underwent plausibility checks and a validation with the catchment areas of 348 monitoring stations across Germany. To this network, we assigned the longest intersecting or the next downstream WB code. To account for geometric inaccuracies we revised spurious intersections resulting in splittings and cycles in the WB network. As WB may be ecologically but not hydrologically well defined, we split them at confluences and intersections. The network of drainage basins matched the monitoring stations with a Nash-Sutcliffe efficiency of 1.00. The final WB network contained 11 005 out of the 11 586 original WBs longer than 1 m. The corresponding local catchment areas range from <<0.0001 to 446 km², with a median of 10 km². The dataset combines the requirements of hydrological and ecological modelling applications at basin or national scales with the needs of the EU reporting which can foster their acceptance by state authorities and river-basin management.     

Nitrogen,Phosphorus and Primary Production in the Pomeranian Bay

The Pomeranian Bay in the south-western part of the Baltic sea has an area of 4300 km² and a volume of 51.4 km³ and contains a fresh-water inflow of 17.3 km³/a from a catchment area of 137,220 km². There were evaluated 18 investigations of specific dates at 14 stations in the years 1976 … 1978: 229 … 235 hydrochemical measurements and 75 phytoplankton investigations. It can be demonstrated by multiple regression analyses that the nutrient concentrations are mainly determined by the fresh-water inflow and the mixing ratios, phytoplankton having a secondary effect. Of the nutrients mainly ammonium influences the phytoplankton development and the oxygen production, the full utilization of the nitrogen stock being limited by an N/P ratio of 48 in the surface water and of 41 in the bottom water layers. Obviously, a limitation of the primary production is out of the question due to the high turnover rates of phosphorus. The N/P ratio is also a clear evidence of the great influence of the inflowing nitrate-rich freshwater on the nutrient situation of the bay.     

Evaluation of the crustal deformations in the northern region of Lake Nasser (Egypt) derived from 8 years of GPS campaign observations

The proper evaluation of crustal deformations in the Aswan (Egypt) region is crucial due to the existence of one major artificial structure: the Aswan High Dam. This construction induced the creation of one of the major artificial lakes: Lake Nasser, which has a surface area of about 5200 km² with a maximum capacity of 165 km³. The lake is nearly 550 km long (more than 350 km within Egypt and the remainder in Sudan) and 35 km across at its widest point. Great attention has focused on this area after the November 14, 1981 earthquake (M_L = 5.7), with its epicenter southwest of the High Dam.In order to evaluate the present-day kinematics of the region, its relationship with increasing seismicity, and the possible influence of the Aswan High Dam operation, a network of 11 GPS sites was deployed in the area. This network has been reobserved every year since 2000 in campaign style. We present here the results of the analysis of the GPS campaign time-series. These time-series are already long enough to derive robust solutions for the motions of these stations. The computed trends are analyzed within the framework of the geophysical and geological settings of this region. We show that the observed displacements are significant, pointing to a coherent intraplate extensional deformation pattern, where some of the major faults (e.g., dextral strike-slip Kalabsha fault and normal Dabud fault) correspond to gradients of the surface deformation field. We also discuss the possible influence of the water load on the long-term deformation pattern.     

Rapid assessment of field erosion and sediment transport pathways in cultivated catchments after heavy rainfall events

This paper explores a scale‐adapted erosion mapping method which aims at a rapid assessment of field erosion and sediment transport pathways in catchments up to several square kilometres and compares the results with the output of a well‐known erosion model (LISEM). The mapping method is based on an event‐defined classification scheme of erosion intensity (zero, weak, moderate and strong) that is applied to arable fields, in combination with incision measurements of erosion features for each erosion intensity class on a small sample of fields. Sediment deposition is classified on the basis of quantity indicators and abundance. In addition, relevant conditions and erosion factors are determined for each field. The method was applied to an agricultural catchment (4·2 km²) in the Sundgau (Alsace), after a short but violent thunderstorm in May 2001, to illustrate its potential use and its limitations. The rainfall event led to strong erosion on the arable fields and a muddy flow that caused significant damage in the built‐up area. On the basis of the analyses of the incision measurements in combination with the mapping of erosion intensity classes, total erosion for the catchment was estimated as 15 000 t (an average of about 36 t[sol ]ha). Sediment deposition was found to occur in three major locations: (1) in thalwegs at the interface between maize and downslope winter wheat fields, (2) in downslope headlands where the flow direction suddenly changed due to oriented tillage structures in the perpendicular direction, and (3) the lowest corners of fields which collect all the runoff from the field. Preliminary data analyses suggest that erosion intensity is related to field size and[sol ]or tillage direction and to slope morphology. Model output (LISEM) appeared to depend more strongly on slope gradient than the results obtained with the mapping method. The method yields a database, which can be used as a foundation for conservation strategies in small regions with similar land use and geomorphology. The mapping and modelling methods are compared, and their complementary aspects are highlighted. Copyright © 2005 John Wiley & Sons, Ltd.     

Magnetic measurements on La Soufriere Volcano, Guadeloupe (Lesser Antilles), 1976–1984: A re-examination of the volcanomagnetic effects observed during the volcanic crisis of 1976–1977

During the seismovolcanic crisis of 1976–1977 at La Soufrière on Guadeloupe, a magnetic network of 12 reference markers was set up. Measurements of the intensity of the earth's magnetic field, carried out up to once a day at each marker, showed volcano-magnetic variations of several nanoteslas (nT). The variations, at certain markers, were more or less concealed by transient magnetic variations due to anomalies in conductivity. As early as 1978, measurements were resumed and a telemetering network was coupled with the network of reference markers, to which 4 new markers were added. A detailed study of conductivity anomalies was carried out on the entire volcano. Contrasts in conductivity linked to the existence of a superficial conducting surface, on a SSW/NNE axis, located south of the volcano, caused a great lack of homogeneity in the field variations measured at the surface. Variations greater than about 10 nT appeared in the difference in intensity of the earth's magnetic field between two stations.No long-term magnetic variation was observed between 1978 and 1984. On the network of markers, the accuracy of measurements of volcanic effects was at best 2 nT. Measurements carried out on the telemetering network during the night refined these results, since their accuracy was 1 nT. The only significant volcanic crisis between 1978 and 1984 (5–7 January 1981) seems to be observed by telemetering stations. All the measurements carried out in periods of volcanic inactivity make it possible to re-examine the crisis of 1976–1977. Though volcanomagnetic effects over short periods cannot be accurately determined, variations with a time constant of several weeks were present over the entire volcano. These variations were as high as 7–8 nT in remote stations and they can be linked to the three major phases of eruptive activity at La Soufrière during the crisis of 1976–1977.     

Estimation of rainfall fields using commercial microwave communication networks of variable density

The use of commercial microwave radio networks which are a part of cellular communication infrastructure for mapping of the near-the-ground rainfall is challenging for many reasons: the network geometry in space is irregular, the distribution of links by frequencies and polarizations is inhomogeneous, and measurements of rain-induced attenuation are distorted by quantization. A non-linear tomographic model over a variable density grid is formulated, and its applicability and performance limits are studied by means of a simulated experiment using a model of a real microwave network. It is shown that the proposed technique is capable to accurately measure integrated near-the-ground rainfall amounts over the area of 3200 km² with a bias smaller than 10%. In urban area, where the density of microwave links is high, the average correlation in space between the simulated model and reconstructed rainfall fields reaches 0.89 over the variable density grid with average cell size of 5.7 km² and 0.74 when interpolated into the rectangular grid with pixel size 0.775 × 0.775 km², for the quantization interval of 0.1 dB.     

An analytical solution for rapidly predicting post-fire peak streamflow for small watersheds in southern California

Following wildfires, the probability of flooding and debris flows increase, posing risks to human lives, downstream communities, infrastructure, and ecosystems. In southern California (USA), the Rowe, Countryman, and Storey (RCS) 1949 methodology is an empirical method that is used to rapidly estimate post-fire peak streamflow. We re-evaluated the accuracy of RCS for 33 watersheds under current conditions. Pre-fire peak streamflow prediction performance was low, where the average R² was 0.29 and average RMSE was 1.10 cms/km² for the 2- and 10-year recurrence interval events, respectively. Post-fire, RCS performance was also low, with an average R² of 0.26 and RMSE of 15.77 cms/km² for the 2- and 10-year events. We demonstrated that RCS overgeneralizes watershed processes and does not adequately represent the spatial and temporal variability in systems affected by wildfire and extreme weather events and often underpredicted peak streamflow without sediment bulking factors. A novel application of machine learning was used to identify critical watershed characteristics including local physiography, land cover, geology, slope, aspect, rainfall intensity, and soil burn severity, resulting in two random forest models with 45 and five parameters (RF-45 and RF-5, respectively) to predict post-fire peak streamflow. RF-45 and RF-5 performed better than the RCS method; however, they demonstrated the importance and reliance on data availability. The important parameters identified by the machine learning techniques were used to create a three-dimensional polynomial function to calculate post-fire peak streamflow in small catchments in southern California during the first year after fire (R² = 0.82; RMSE = 6.59 cms/km²) which can be used as an interim tool by post-fire risk assessment teams. We conclude that a significant increase in data collection of high temporal and spatial resolution rainfall intensity, streamflow, and sediment loading in channels will help to guide future model development to quantify post-fire flood risk.     

The eruptive history of the Tequila volcanic field, western Mexico: ages, volumes, and relative proportions of lava types

The eruptive history of the Tequila volcanic field (1600 km²) in the western Trans-Mexican Volcanic Belt is based on ⁴⁰Ar/³⁹Ar chronology and volume estimates for eruptive units younger than 1 Ma. Ages are reported for 49 volcanic units, including Volcán Tequila (an andesitic stratovolcano) and peripheral domes, flows, and scoria cones. Volumes of volcanic units 1 Ma were obtained with the aid of field mapping, ortho aerial photographs, digital elevation models (DEMs), and ArcGIS software. Between 1120 and 200 kyrs ago, a bimodal distribution of rhyolite (~35 km³) and high-Ti basalt (~39 km³) dominated the volcanic field. Between 685 and 225 kyrs ago, less than 3 km³ of andesite and dacite erupted from more than 15 isolated vents; these lavas are crystal-poor and show little evidence of storage in an upper crustal chamber. Approximately 200 kyr ago, ~31 km³ of andesite erupted to form the stratocone of Volcán Tequila. The phenocryst assemblage of these lavas suggests storage within a chamber at ~2–3 km depth. After a hiatus of ~110 kyrs, ~15 km³ of andesite erupted along the W and SE flanks of Volcán Tequila at ~90 ka, most likely from a second, discrete magma chamber located at ~5–6 km depth. The youngest volcanic feature (~60 ka) is the small andesitic volcano Cerro Tomasillo (~2 km³). Over the last 1 Myr, a total of 128±22 km³ of lava erupted in the Tequila volcanic field, leading to an average eruption rate of ~0.13 km³/kyr. This volume erupted over ~1600 km², leading to an average lava accumulation rate of ~8 cm/kyr. The relative proportions of lava types are ~22–43% basalt, ~0.4–1% basaltic andesite, ~29–54% andesite, ~2–3% dacite, and ~18–40% rhyolite. On the basis of eruptive sequence, proportions of lava types, phenocryst assemblages, textures, and chemical composition, the lavas do not reflect the differentiation of a single (or only a few) parental liquids in a long-lived magma chamber. The rhyolites are geochemically diverse and were likely formed by episodic partial melting of upper crustal rocks in response to emplacement of basalts. There are no examples of mingled rhyolitic and basaltic magmas. Whatever mechanism is invoked to explain the generation of andesite at the Tequila volcanic field, it must be consistent with a dominantly bimodal distribution of high-Ti basalt and rhyolite for an 800 kyr interval beginning ~1 Ma, which abruptly switched to punctuated bursts of predominantly andesitic volcanism over the last 200 kyrs.Electronic Supplementary Material Supplementary material is available in the online version of this article at Editorial responsility: J. Donnelly-NolanThis revised version was published online in January 2005 with corrections to Tables 1 and 3.An erratum to this article can be found at