Basin Topography Research Articles

Reorganization of river networks under changing spatiotemporal precipitation patterns: An optimal channel network approach

AbstractWe investigate the impact of changing nonuniform spatial and temporal precipitation patterns on the evolution of river networks. To achieve this, we develop a two‐dimensional optimal channel network (OCN) model with a controllable rainfall distribution to simulate the evolution of river networks, governed by the principle of minimum energy expenditure, inside a prescribed boundary. We show that under nonuniform precipitation conditions, river networks reorganize significantly toward new patterns with different geomorphic and hydrologic signatures. This reorganization is mainly observed in the form of migration of channels of different orders, widening or elongation of basins as well as formation and extinction of channels and basins. In particular, when the precipitation gradient is locally increased, the higher‐order channels, including the mainstream river, migrate toward regions with higher precipitation intensity. Through pertinent examples, the reorganization of the drainage network is quantified via stream parameters such as Horton‐Strahler and Tokunaga measures, order‐based channel total length and river long profiles obtained via simulation of three‐dimensional basin topography, while the hydrologic response of the evolved network is investigated using metrics such as hydrograph and power spectral density of simulated streamflows at the outlet of the network. In addition, using OCNs, we investigate the effect of orographic precipitation patterns on multicatchment landscapes composed of several interacting basins. Our results show that network‐inspired methods can be utilized as insightful and versatile models for directly exploring the effects of climate change on the evolution of river drainage systems.

Coupling sedimentation and tectonic control: Pleistocene evolution of the central Po Basin

This study reports, for the first time in a wide basin area, sedimentation rates calculated on decompacted sediments from a 3D model and not only in wells or along sections. The 3D geological model is used here to analyse the Pleistocene evolution of the central Po Basin. A sequential restoration-and-decompaction workflow is used to obtain six detailed pictures of the basin topography unaffected by sedimentary compaction and tectonic signals in different moments. The maps illustrate the progressive infilling of the basin and the migration of the main depocenters. The sedimentation rate values are obtained using a 3D analysis of the thicknesses; the results highlight the progressive reduction in the sediment supply (from 2.83±0.19 mm/yr in the Calabrian to 0.39±0.05 mm/yr in the Upper Pleistocene) and the difference in sedimentation rate in different depositional environments. Moreover the study focuses on the Pleistocene sedimentation and tectonic history of the Piadena anticline, in order to calculate uplift vs sedimentation rates in an area located far from the main tectonic structures. The obtained results are comparable with literature data and point out the magnitude and the interference of tectonic, sedimentary and climatic processes in the same area, in different moment during the Pleistocene. The workflow applied in this study can be used to discriminate, and in some case to measure, the elusive synsedimentary tectonic signal related to compressive structures growing in a general subsiding basin.

Subsidence control on river morphology and grain size in the Ganga Plain

The Ganga Plain represents a large proportion of the current foreland basin to the Himalaya. The Himalayan-sourced waters irrigate the Plain via major river networks that support approximately 10 percent of the global population. However, some of these rivers are also the source of devastating floods. The tendency for some of these rivers to flood is directly linked to their large scale morphology. In general, the rivers that drain the east Ganga Plain have channels that are perched at a higher elevation relative to their floodplain, leading to more frequent channel avulsion and flooding. In contrast, those further west have channels that are incised into the floodplain and are historically less prone to flooding. Understanding the controls on these contrasting river forms is fundamental to determining the sensitivity of these systems to projected climate change and the growing water resource demands across the Plain. Here, we present a new basin scale approach to quantifying floodplain and channel topography that identifies areas where channels are super-elevated or entrenched relative to their adjacent floodplain. We explore the probable controls on these observations through an analysis of basin subsidence rates, sediment grain size data and sediment supply from the main river systems that traverse the Plain (Yamuna, Ganga, Karnali, Gandak and Kosi rivers). Subsidence rates are approximated by combining basement profiles derived from seismic data with known convergence velocities; results suggest a more slowly subsiding basin in the west than the east. Grain size fining rates are also used as a proxy for relative subsidence rates along the strike of the basin; the results also indicate higher fining rates (and hence subsidence rates for given sediment supply) in the east. By integrating these observations, we propose that higher subsidence rates are responsible for a deeper basin in the east with perched, low gradient river systems that are relatively insensitive to climatically driven changes in base-level. In contrast, the lower subsidence rates in the west are associated with a higher elevation basin topography, and entrenched river systems recording climatically induced lowering of river base-levels during the Holocene.

Quantifying wintertime boundary layer ozone production from frequent profile measurements in the Uinta Basin, UT, oil and gas region

AbstractAs part of the Uinta Basin Winter Ozone Study, January–February 2013, we conducted 937 tethered balloon‐borne ozone vertical and temperature profiles from three sites in the Uinta Basin, Utah (UB). Emissions from oil and gas operations combined with snow cover were favorable for producing high ozone‐mixing ratios in the surface layer during stagnant and cold‐pool episodes. The highly resolved profiles documented the development of approximately week‐long ozone production episodes building from regional backgrounds of ~40 ppbv to >165 ppbv within a shallow cold pool up to 200 m in depth. Beginning in midmorning, ozone‐mixing ratios increased uniformly through the cold pool layer at rates of 5–12 ppbv/h. During ozone events, there was a strong diurnal cycle with each succeeding day accumulating 4–8 ppbv greater than the previous day. The top of the elevated ozone production layer was nearly uniform in altitude across the UB independent of topography. Above the ozone production layer, mixing ratios decreased with height to ~ 400 m above ground level where they approached regional background levels. Rapid clean‐out of ozone‐rich air occurred within a day when frontal systems brought in fresh air. Solar heating and basin topography led to a diurnal flow pattern in which daytime upslope winds distributed ozone precursors and ozone in the Basin. NOx‐rich plumes from a coal‐fired power plant in the eastern sector of the Basin did not appear to mix down into the cold pool during this field study.

Flow Regimes over a Basin Induced by Upstream Katabatic Flows—An Idealized Modeling Study

Abstract Idealized two-dimensional model simulations are performed to study the frequent nocturnal occurrence of downslope-windstorm-type flows in Arizona’s Meteor Crater. The model topography is a simplified representation of the Meteor Crater and its surroundings, with an approximately 1° mesoscale slope upstream and downstream of the crater basin. A strong surface-based inversion and a katabatic flow develop above the mesoscale slope as a result of radiational cooling. The temperature and flow profiles are evaluated against observations over low-angle slopes from two field campaigns, showing that the model’s turbulence parameterization has a strong impact on the near-surface conditions. The interaction of the katabatic flow with the basin topography leads to the formation of waves and hydraulic jumps over the basin. The simplified two-dimensional simulations show good qualitative agreement with observations of downslope-windstorm-type flows from the Meteor Crater. The sensitivity of the flow solution over the basin to basin depth, basin width, and background wind speed is investigated. The resulting flow regimes include a sweeping of the basin atmosphere, a wake over the upstream crater sidewall, waves over the basin with one or two wave crests, and a hydraulic jump. The regimes are discussed in the context of stratified flow over mountains.

The acute effects of rapid changes in air pollutant levels on cardiovascular disease in Taipei City, Taiwan

Introduction: Long-range transport air pollution models have suggested that air pollutants may be transported with China monsoon across continents and ocean basins to influence neighbouring countries’ air quality. As air pollution increases morbidity and mortality of cardiovascular disease (CAD), we conducted a study to explore the associations between air pollutant levels and outpatient visits for CAD during dust storm events in Taipei City, the capital of Taiwan, where the population density is high and the air quality is affected by the basin topography and heavy traffic. Methods: As defined by the Taiwan Environmental Protection Administration (EPA), a dust storm event is an episode with an average PM10 level above 100ug/m3. We obtained data on air pollutants from the EPA monitoring stations in Taipei City, including Shilin, Datong, Gutting, Zhongshan, and Wanhua Stations. Data on daily outpatient visits for CAD (ICD-9 codes 460 to 510) in Taipei City from 2005 to 2010 were obtained from the National Health Insurance Research Database. Results: We identified 229,248 CAD outpatient visits during the study period. Time series models showed that CAD outpatient visits were associated with CO (same day and with a 2-day lag), NO, NO2 (same day and with a 3-day lag) and a weekend effect. In addition, we identified 3,850 CAD cases during dust storm events. We compared 2-days average concentration changes in air pollutants before and during the events and found that O3 and PM10 were higher during the events, but CO, NO, and NO2 decreased during the events. We found that levels of O3 and SO2 were associated with CAD outpatient visits on the same day and with a 2-day lag. We also found that PM10 and PM2.5 levels were associated with CAD outpatient visits on the same day and with 1- and 2-day lags. Conclusions: This study provides evidence supporting the effects of O3, SO2, PM10, and PM2.5 on CAD outpatient visits during dust storm events.

Analysis of interactive effects of DEM resolution and basin subdivision level on runoff simulation in Kaidu River Basin, China

Uncertainties in spatial data associated with basin topography, drainage networks, and land cover characteristics may affect the performance of runoff simulation. Such uncertainties are mainly derived from selection of digital elevation model (DEM) resolution and basin subdivision level. This study focuses on assessing the effects of DEM resolution and basin subdivision level on runoff simulation with a semi-distributed land use-based runoff process model. Twenty-four scenarios based on various DEM resolutions and subdivision levels are analyzed for the Kaidu River Basin. Results can be used for quantifying the uncertainty of input data about spatial information on model simulation, disclosing the interaction between DEM resolution and subdivision level, as well as identifying the optimal system inputs. Results show that the model performance could be enhanced with the increased subdivision level. Results also reveal that the interaction of DEM resolution and subdivision level has slight effects on modeling outputs. Multi-objective fuzzy evaluation is used to further examine the uncertainty in DEM resolution and basin subdivision level on model performance. The results indicate an optimal combination of input parameters is suitable for Kaidu River Basin which could lead to more reliable results of the hydrological simulation.

Quaternary fluvial tufas of Sarıkavak area, southwestern Turkey: Facies and depositional systems

Abstract In the Quaternary Sarikavak fluvial tufa deposits, situated in south-western Turkey, different facies have been identified and their mutual relationships have been unravelled. This tufa formation is located at the northern part of Acigol Graben. The development of the Sarikavak tufas represents typical fluvial and fluvio-palustrine environments. In total eight tufa lithofacies have been differentiated, namely: moss tufa facies, oncolitic tufa facies, stromatolitic tufa facies, phytoclastic tufa facies, intraclastic tufa facies, extra-formational clastic tufa facies, sapropelitic tufa facies, and palaeosol. Preliminary U/Th datings indicate that these deposits formed prior to 219 ka and continued until 80 ka (MIS 7 till 5). δ13C signatures (0.78‰ to −1.63‰ V-PDB) best can be explained by limestone dissolution processes or respiration from C4 plant vegetation into the soil or both. For that reason, the Sarikavak tufa deposits can be classified as ‘travitufa’ which precipitated in a distal facies system of travertine occurrences. δ18O values (−7.49‰ to −10.83‰ V-PDB) of the whole data set reflect some significant changes, which is interpreted in terms of temperature variations reflecting warm and cold periods among MIS 7 (interglacial), MIS 6 (glacial) and MIS 5 (interglacial). The development of the Sarikavak tufa deposits are related to the Maymundagi fault that borders the Acigol Graben in the north. This fault and its synthetic fault segments play a pivotal role with regard to the palaeo-flow direction of water and control the basin topography. These structural structures are likely responsible for all active and ancient springs in the study area, as well as their respective carbonate precipitates.

Landslides in moraines as triggers of glacial lake outburst floods: example from Palcacocha Lake (Cordillera Blanca, Peru)

Studies focusing on moraine deposits which slide into glacial lakes are scarce, even though they can trigger impact waves responsible for generating glacial lake outburst floods. We focused on landslides in lateral moraines as possible triggers. Detailed geomorphological, geophysical, and satellite radar interferometric investigations of the Palcacocha Lake moraine (Cordillera Blanca, Peru) together with laboratory tests on samples from the site provided data for slope stability calculations using GeoSlope software and hydrodynamic impact wave modeling using the Iber code. We identified landslides that could affect Palcacocha Lake and calculated their stability (factor of safety) under specified conditions, including variable water saturation and earthquake effects. Calculations showed that the moraine slopes are close to the threshold value (Fs = 1) for stability and are especially sensitive to water saturation. The height of impact waves triggered by a landslide in 2003 and the potential wave heights from newly identified, possibly active landslides were calculated, based on landslide volume estimates, detailed lake bathymetry, and basin topography. Results show that potential future landslide-triggered waves could have similar properties to the 2003 impact wave. Evidence gathered in this study suggests that glacial lake outburst floods triggered by landslides from moraines, however, would be probably smaller than floods resulting from other types of slope processes (e.g., ice/rock avalanches) if dam breach is not taken into account. This assumption has to be critically evaluated against site-specific conditions at a given lake and any possible environmental factors, such as climate change or earthquake that may mobilize larger volumes of moraine material.

Vigorous convection as the explanation for Pluto's polygonal terrain.

Pluto's surface is surprisingly young and geologically active. One of its youngest terrains is the near-equatorial region informally named Sputnik Planum, which is a topographic basin filled by nitrogen (N2) ice mixed with minor amounts of CH4 and CO ices. Nearly the entire surface of the region is divided into irregular polygons about 20-30 kilometres in diameter, whose centres rise tens of metres above their sides. The edges of this region exhibit bulk flow features without polygons. Both thermal contraction and convection have been proposed to explain this terrain, but polygons formed from thermal contraction (analogous to ice-wedges or mud-crack networks) of N2 are inconsistent with the observations on Pluto of non-brittle deformation within the N2-ice sheet. Here we report a parameterized convection model to compute the Rayleigh number of the N2 ice and show that it is vigorously convecting, making Rayleigh-Bénard convection the most likely explanation for these polygons. The diameter of Sputnik Planum's polygons and the dimensions of the 'floating mountains' (the hills of of water ice along the edges of the polygons) suggest that its N2 ice is about ten kilometres thick. The estimated convection velocity of 1.5 centimetres a year indicates a surface age of only around a million years.

On the ability of large-scale hydrological models to simulate land use and land cover change impacts in Amazonian basins

ABSTRACTThe MHD-INPE model was applied in the Ji-Parana Basin, a 30 000 km2 catchment located in the southwest of the Amazon Basin which has lost more than 50% of its forest since the 1980s, to simulate land use and land cover change impacts on runoff generation process and how they are related to basin topography. Simulation results agree with observational studies in the sense that fast response processes are significant in sub-basins with steep slopes while in basins with gentle topography, the impacts are most visible in slow-response hydrological processes. On the other hand, the model is not able to capture the dependence of LUCC impacts on spatial scales. These discrepancies are probably associated with limitations in the spatial representation of heterogeneities within the model, which become more relevant at larger scales. We also tested the hypothesis that secondary forest growth should be able to compensate the decrease in evapotranspiration due to forest–cropland or forest–grassland conversion at a regional scale. Results showed that despite the small fraction of secondary forest estimated on the basin, the higher evapotranspiration efficiency of this type of forest counterbalances a large fraction of the LUCC impacts on evapotranspiration. This result suggests that enhanced transpiration due to secondary forest could explain, at least in part, the lack of clear LUCC signals in discharge series at larger scales.EDITOR D. Koutsoyiannis; ASSOCIATE EDITOR T. Wagener

A modified landform development model for the topography of drained thermokarst lake basins in fine‐grained sediments

AbstractPermafrost degradation associated with the expansion of thermokarst lakes is commonly interrupted by catastrophic drainage. Subsequently, in tundra areas, permafrost aggradation in drained basins leads to uneven topography characterized by raised centres and wet, depressed margins. The genesis of such topography has been investigated in Old Crow Flats (OCF), a glaciolacustrine plain in the continuous permafrost of northern Yukon. The thermokarst lakes of OCF have a mean depth of only 1.5 m because excess ice is dominantly found only in the uppermost 10 m of the ground. Surface conditions were measured in three drained thermokarst lake basins, including relief, snow conditions, ground temperatures, near‐surface ground ice, and sediment stratigraphy. Four nearby lakes provided information on wave base, shore recession patterns, and bathymetry before drainage: the bottoms of these lakes were not raised in the centre. An elevation difference of up to 2 m was recorded between drained basin margins and centres but was not associated with variations in ice‐wedge density or segregated ice content. Hence basin topography was not controlled by differences in volumetric ground‐ice content between margins and centres. We propose that transport of fine sediment away from eroding lake margins during lake development is the primary mechanism for the genesis of depressed margins and raised centres in drained basins of OCF. Over time, the transport results in the deposition of more and finer sediment in the central parts of lakes, where the lake bottom has subsided below wave base, than at the shallow margins, where resuspension by wave action occurs frequently. This difference in sediment volume is revealed in the topography after drainage, when permafrost aggrades in the lake‐bottom sediment and underlying talik. Copyright © 2016 John Wiley & Sons, Ltd.

Insights into surface runoff on early Mars from paleolake basin morphology and stratigraphy

We present observations on the morphology and stratigraphy of more than 400 paleolake basins on Mars. We show that there are two distinct classes of Martian paleolake basins: (1) paleolakes fed by regionally integrated valley networks (N = 251), and (2) paleolakes fed by isolated inlet valleys not integrated into broader regional drainage systems (N = 174). We conclude that valley network–fed paleolakes primarily formed prior to approximately the Noachian-Hesperian boundary, ca. 3.7 Ga, while isolated inlet valley paleolakes primarily formed later in Martian history. All 174 isolated inlet valley paleolakes are closed-basin lakes; however, there are surprisingly few (31) valley network–fed closed-basin lakes compared to a large number (220) of valley network–fed open-basin lakes. This observation is consistent with declining levels of fluvial activity over time on the Martian surface. Our results imply that during the era of valley network formation, ∼90% of topographic basins breached by an inlet valley had sufficiently high ratios of water influx to losses to fill, overtop, and form an outlet valley. This conclusion provides an important constraint on the balance between surface runoff production and water losses on early Mars that must be satisfied by any model of the early Martian climate and hydrologic cycle.

Is consolidation drainage an indirect mechanism for increased abundance of cattail in northern prairie wetlands?

In the Prairie Pothole Region of North America, disturbances to wetlands that disrupt water-level fluctuations in response to wet–dry climatic conditions have the potential to alter natural vegetative communities in favor of species that proliferate in stable environments, such as cattail (Typha spp.). We evaluated the effect of water-level dynamics during a recent fluctuation in wet–dry conditions on cattail coverage within semipermanently and permanently ponded wetlands situated in watersheds with different land use and amounts of wetland drainage. We found that ponded water depth increase was significantly greater in wetlands where water levels were not near the spill point of the topographic basin, where banks were steeper, and in larger wetlands where past dry conditions had less influence on change in pond area. Proportion of the wetland covered by cattail was negatively correlated with increased water depth, bank slope and pond area. Our observations provide evidence that cattail coverage in prairie wetlands is regulated by water-level fluctuations and that land use surrounding the wetland might have an indirect effect on cattail coverage by altering water-level response to wet–dry climate conditions. For example, drainage of smaller wetlands into larger wetlands that are characterized by more permanent hydroperiods, leads to stabilized water levels near their spill point and is therefore a potential mechanism for increased cattail abundance in the northern prairie region.

Rheomorphic ignimbrites of the Rogerson Formation, central Snake River plain, USA: record of mid-Miocene rhyolitic explosive eruptions and associated crustal subsidence along the Yellowstone hotspot track

Rogerson Graben, USA, is critically placed at the intersection between the Yellowstone hotspot track and the southern projection of the west Snake River rift. Eleven rhyolitic members of the re-defined, ≥420-m-thick, Rogerson Formation record voluminous high-temperature explosive eruptions, emplacing extensive ashfall and rheomorphic ignimbrite sheets. Yet, each member has subtly distinct field, chemical and palaeomagnetic characteristics. New regional correlations reveal that the Brown’s View ignimbrite covers ≥3300 km2, and the Wooden Shoe ignimbrite covers ≥4400 km2 and extends into Nevada. Between 11.9 and ∼8 Ma, the average frequency of large explosive eruptions in this region was 1 per 354 ky, about twice that at Yellowstone. The chemistry and mineralogy of the early rhyolites show increasing maturity with time possibly by progressive fractional crystallisation. This was followed by a trend towards less-evolved rhyolites that may record melting and hybridisation of a mid-crustal source region. Contemporaneous magmatism-induced crustal subsidence of the central Snake River Basin is recorded by successive ignimbrites offlapping and thinning up the N-facing limb of a regional basin-margin monocline, which developed between 10.59 and 8 Ma. The syn-volcanic basin topography contrasted significantly with the present-day elevated Yellowstone hotspot plateau. Concurrent basin-and-range extension produced the N-trending Rogerson Graben: early uplift of the Shoshone Hills (≥10.34 Ma) was followed by initiation of the Shoshone Fault and an E-sloping half-graben (∼10.3–10.1 Ma). The graben asymmetry then reversed with initiation of the Brown’s Bench Fault (≥8 Ma), which remained intermittently active until the Pliocene.

Distributed modeling of ablation (1996–2011) and climate sensitivity on the glaciers of Taylor Valley, Antarctica

ABSTRACTThe McMurdo Dry Valleys of Antarctica host the coldest and driest ecosystem on Earth, which is acutely sensitive to the availability of water coming from glacial runoff. We modeled the spatial variability in ablation and assessed climate sensitivity of the glacier ablation zones using 16 years of meteorological and surface mass-balance observations collected in Taylor Valley. Sublimation was the primary form of mass loss over much of the ablation zones, except for near the termini where melt, primarily below the surface, dominated. Microclimates in ~10 m scale topographic basins generated melt rates up to ten times higher than over smooth glacier surfaces. In contrast, the vertical terminal cliffs on the glaciers can have higher or lower melt rates than the horizontal surfaces due to differences in incoming solar radiation. The model systematically underpredicted ablation for the final 5 years studied, possibly due to an increase of windblown sediment. Surface mass-balance sensitivity to temperature was ~−0.02 m w.e. K−1, which is among the smallest magnitudes observed globally. We also identified a high sensitivity to ice albedo, with a decrease of 0.02 having similar effects as a 1 K increase in temperature, and a complex sensitivity to wind speed.

Relative tectonics and debris flow hazards in the Beijing mountain area from DEM-derived geomorphic indices and drainage analysis

The geomorphic setting of the tectonically active area around Beijing is a result of complex interactions involving Yanshan neotectonic movements and processes of erosion and deposition. The Beijing Mountain study area contains the junction of two mountain ranges (the Yanshan Mountains and the Taihang Mountains). Tectonic activity has significantly influenced the drainage system and the geomorphic situation in the area, leading to a high probability of the development of debris flows, which is one of the major abrupt geological disasters in the region. Based on 30-m-resolution ASTER GDEM data, a total of 752 drainage basins were extracted using ArcGIS software. A total of 705 debris flow valleys were visually interpreted from ALOS satellite images and published documents. Seven geomorphic indices were calculated for each basin including the relief amplitude, the hypsometric integral, the stream length gradient, the basin shape indices, the fractal dimension, the asymmetry factor, and the ratio of the valley floor width to the height. These geomorphic indices were divided into five classes and the ratio of the number of the debris flow valleys to the number of the drainage basins for each geomorphic index was computed and analyzed for every class. Average class values of the seven indices were used to derive an index of relative active tectonics (IRAT). The ratio of the number of the debris flow valleys to the number of the drainage basins was computed for every class of IRAT. The degree of probable risk level was then defined from the IRAT classes. Finally, the debris flow hazard was evaluated for each drainage basin based on the combined effect of probable risk level and occurrence frequency of the debris flows. The result showed a good correspondence between IRAT classes and the ratio of the number of the debris flow valleys to the number of the drainage basins. Approximately 65% of the drainage basins with occurred debris flow valleys are at a high risk level, while 43% of the drainage basins without occurred debris flow valleys are at a high risk level. A comparison with results from past studies demonstrated that the accuracy of these findings is greater than 85%, indicating that the basin topography created by rapid tectonic deformations is more favorable for debris flows.

Asynchronous timing of extension and basin formation in the South Rhodope core complex, SW Bulgaria, and northern Greece

AbstractUpper crustal extensional structures range from steep normal faults to shallow‐dipping detachments. The relationship between extension and formation of synkinematic hanging wall basins including their relative timing is not well understood. The South Rhodope core complex, Southern Balkans, has experienced extension for >40 Ma leading to a number of extensional structures and Cenozoic sedimentary basins. We present new bedrock and basin detrital zircon and apatite (U‐Th‐Sm)/He ages from the Pirin and Rila Mountains and the Sandanski basin. Results identify three episodes of Cenozoic extension in SW Bulgaria accommodated by (1) the Eocene/Oligocene Mesta detachment; (2) the early to middle Miocene Gorno Spanchevo fault (circa 18–15 Ma), which is the northern prolongation of the Strymon low‐angle detachment; and (3) the late Miocene West Pirin fault (≤10 Ma). Detachment faulting on the Strymon fault accommodated tens of kilometers of ENE‐WSW extension and created ~1500 m topographic relief, but because the resulting hillslopes were gentle (≤10°), extension did not lead to enhanced footwall erosion or formation of a hanging wall basin. In contrast, the West Pirin normal fault resulted in mostly vertical motion of its footwall causing steep topography, rapid erosion, and formation of the synrift Sandanski basin. Digital topographic analysis of river channel profiles identifies the latest episodes of deformation including westward tilting of the Sandanski and Strymon basins and Quaternary N‐S extension. This study demonstrates that basin formation in the South Rhodope core complex is related to normal faulting postdating the main episode of crustal stretching by detachment faulting.

Opposite seasonality of the aerosol optical depth and the surface particulate matter concentration over the north China Plain

Abstract Great difference exists in the aerosol optical depth (AOD) between summer and winter over the North China Plain (NCP). Monthly mean AOD at 550 nm derived from the MODIS (MODerate Resolution Imaging Spectroradiometer) products during 2000–2014 over the area of 30–40° N and 110–125° E exhibits an annual maximum in June (0.855 ± 0.130) and a minimum in December (0.381 ± 0.032). This seasonality of AOD is in the opposite phase with the surface particulate matter (PM) concentration (higher in winter and lower in summer). The possible causes for the higher AOD in June (compared with December) include (a) a higher boundary layer height (BLH) that results in more efficient transport and mixing of aerosol particles to a higher altitude (corresponding to a lower particle concentration near surface) as revealed by the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations profile, (b) a higher relative humidity (RH) due to the inshore monsoon circulation that leads to enhancement of aerosol extinction, (c) emission from the regional open stalk burning in the summer harvest season (as seen from MODIS fire products), and (d) the typical eastward open topographical basin over NCP. Under the assumption that the aerosol and water vapor are well mixed within the boundary layer, analysis on multi-year average shows that the differences in BLH, RH and surface PM concentration can explain up to 81% of the variance of monthly averaged AOD over NCP. A preliminarily hypothesis is also suggested to interpret the shift of AOD pattern from winter to summer with an abrupt increase of AOD from May to June, as well as an increase of surface PM 2.5 concentration over NCP during the early phase of northward progress of the East Asia summer monsoon front.

A semi-physical sediment yield model for estimation of suspended sediment in loess region

Sediment yield is a complex function of many environmental factors including climate, hydrology, vegetation, basin topography, soil types, and land cover. We present a new semi-physical watershed sediment yield model for the estimation of suspended sediment in loess region. This model is composed by three modules in slope, gully, and stream phases. For slope sediment yield, a balance equation is established based on the concept of hydraulic erosion capacity and soil erosion resistance capacity. According to the statistical analysis of watershed characteristics, we use an exponential curve to approximately describe the spatial variability of watershed soil erosion resistance capacity. In gully phase, the relationship between gully sediment concentration and flow velocity is established based on the Bagnold׳ stream power function. In the stream phase, we assume a linear dependence of the sediment volume in the reach on the weighted sediment input and output. The proposed sediment yield model is operated in conjunction with a conceptual hydrologic model, and is tested over 16 regions including testing grounds, and small, medium and large watersheds in the loess plateau region in the mid-reach of Yellow River. Our results indicate that the model is reasonable in structure and is able to provide a good simulation of sediment generation and transportation processes at both flood event scale and inter-annual time scale. The proposed model is generally applicable to the watersheds with soil texture similar to that of the loess plateau region in the Yellow River basin in China.