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.     

Mahafir: A water harvesting system in the Eastern Jordan (Badia) Eesert

There are many different water harvesting systems in the Middle East and the operation of one type, the mahafir, was investigated in the Badia Region of Jordan. Mahafir are crescent and rectangular shaped excavations dug into the playa surface, now filled with sediment. Their previous volumes were estimated through topographical survey of the surrounding earth mounds. The average depth of the mahafir was found to be 3.2 m; storing a total water volume of 111,619 m³ at Maharouta and 55,005 m³ at Anka. The mahafir only occupy 4% of the playa surface and their source of water is primarily direct rainfall onto the playa surface augmented by runoff from adjacent slopes. Taking annual rainfalls as an input from 1963 to 1992 and even assuming rainfall harvesting is only 10% effective it appears that the full water storage potential of the mahafir could be met in most years.     

Lahar-Triggering Mechanisms and Hazard at Ruapehu Volcano,New Zealand

Late Holocene volcanic activity at Ruapehu has been characterizedby the generation of small (<10⁵ m³) to very large (>10⁷ m³) lahars and repeated,small to medium (VEI 1-3) tephra-producing eruptions. The Onetapu Formation groupsall lahar deposits that accumulated during the last 2,000 years on the southeastern Ruapehu ring plain. The andesitic tephras are grouped within the Tufa Trig Formation and are intercalated within the laharic sequence. By correlating these two formations with new radiocarbon ages obtained on interbedded paleosols, we reconstruct a detailed volcanic history of Ruapehu for this period.Clast assemblages identified in the laharic sequences record thelithologies of synchronous tephras and rocks within the source region. These assemblages suggest a strong genetic link between the development of Crater Lake, the variation in eruptivestyles, and the production of lahars.Lahar-triggering mechanisms include: (1) flank collapse ofhydrothermally altered and unstable portions of the cone; (2) phreatic and phreatomagmatic eruptions favoring the generation of snow-rich slurries and hyperconcentrated stream flows; (3) suddenCrater Lake rim collapse, releasing large amounts of water inducing debris flows; and (4) eruptions that generate large volumes of tephra on snow-covered slopes, later remobilized by heavy rain.Two major lahars in the Onetapu sequence had a volume 4 × 10⁷ m³, roughly 1 to 2 orders of magnitude larger than the 1953event leading to the Tangiwai disaster (151 casualties). One of these lahars crossed over a lowinterfluve currently separating the Whangaehu River from a stream feeding the Tongariro River,sometime since peat accumulated between AD 1400 and AD 1660. A repetition of such a large-scaleevent would have devastating consequences on the infrastructure, economy and environment withinthe distal areas of the two catchments. The 1995–1996 eruptions were a timely reminder ofthe hazards posed by the volcano.     

Movement of a small slipfaceless dome dune in the Namib Sand Sea, Namibia

The migration of a small slipfaceless dome dune close to the northern edge of the Namib Sand Sea has been measured by topographic survey. The dune dimensions are 45-m wide and 1-m high with a volume of 551 m³ that has been calculated as the difference between the dune's surface elevation and an interdune surface extrapolated from measurements around the edge of the dune. The migration direction, 64°, and distance moved, 90 m, are measured against stakes set out in 1976. The dune has moved about 90 m between 1976 and 1999. This is an average linear migration rate of around 4 m year⁻¹, and is equivalent to an annual sand transport rate of about 1.2 tonnes m⁻¹ year⁻¹. The calculated total potential sand flow in this part of the Namib Desert is 119 tonnes m⁻¹ year⁻¹, and the resultant potential sand flow is 63 tonnes m⁻¹ year⁻¹. The dune migration is therefore about 1% of the total potential sandflow and 2% of the resultant indicating that dune migration is only a small part of total potential sand transport. The results suggest that small slipfaceless dome dunes are very inefficient at trapping sand, and that winds blowing across the interdune in this area are undersaturated with sand.     

Dunes of the Gran Desierto Sand-Sea,Sonora, Mexico

The Gran Desierto Sand-Sea contains dunes of crescentic and star form in simple, compound, and complex varieties. The dunes have developed in bimodal to complex wind regimes of intermediate energy. Transitions from simple through compound to complex crescentic dunes are associated with regional changes in wind regimes. Growth of large star dunes takes place by merging of smaller crescentic and reversing dunes from southerly directions and reworking of sand by northerly and westerly winds. Although wind regimes appear to be the major control of dune morphology in this sand-sea, there is a close correlation between the spacing of simple crescentic dunes and the grain size of the coarse 20th percentile.     

Influence of vegetation cover on sand transport by wind: field studies at Owens Lake,California

Field studies conducted at Owens Lake, California, provide direct measurements of sand flux on sand sheets with zero to 20 per cent cover of salt grass. Results from 12 different sand transport events show that aerodynamic roughness length and threshold wind shear velocity increase with vegetation cover as measured by vertically projected cover and roughness density (λ). This results in a negative exponential decrease in sediment flux with increasing vegetation cover such that sand transport is effectively eliminated when the vertically projected cover of salt grass is greater than 15 per cent. A general empirical model for the relation between sand flux and vegetation cover has been derived and can be used to predict the amount of vegetation required to stabilize sand dune areas. © 1998 John Wiley & Sons, Ltd.     

Mass budgets of the Lambert, Mellor and Fisher Glaciers and basal fluxes beneath their flowbands on Amery Ice Shelf

We used in situ measurements and remote-sensing data sets to evaluate the mass budgets of the Lambert, Mellor and Fisher Glaciers and the basal melting and freezing rates beneath their flowbands on the Amery Ice Shelf. Our findings show the Lambert and Mellor Glaciers upstream of the ANARE Lambert Glacier Basin (LGB) traverse may have positive imbalances of 3.9±2.1 Gt a-1 and 2.1±2.4 Gt a-1, respectively, while the Fisher Glacier is approximately in balance. The upstream region as a whole has a positive imbalance of 5.9±4.9 Gt a-1. The three same glaciers downstream of the ANARE LGB traverse line are in negative imbalance, where the whole downstream region has a negative imbalance of -8.5±5.8 Gt a-1. Overall the mass budgets of the Lambert, Mellor, and Fisher Glaciers are close to bal-ance, and the collective three-glacier system is also nearly in balance with a mass budget of -2.6±6.5 Gt a-1. The significant positive imbalances for the interior basin upstream of the ice-movement stations established in the early 1970s (GL line) reported previously are possibly due to an overestimate of the total accumulation and an underestimate of the ice flux through the GL line. The mean melting rate is -23.0±3.5 m ice a-1 near the southern grounding line, which decreases rapidly downstream, and transitions to refreezing at around 300 km from the southern extremity of the Amery Ice Shelf. Freezing rates along the flowbands are around 0.5±0.1 to 1.5±0.2 m ice a-1. The per-centage of ice lost from the interior by basal melting beneath the flowbands is about 80%±5%. The total basal melting and refreezing beneath the three flowbands is 50.3±7.5 Gt ice a-1 and 7.0±1.1 Gt ice a-1, respectively. We find a much larger total basal melting and net melting than the results for the whole Amery Ice Shelf derived from previous modeling and oceanographic measurements.     

Solution of Lambert's problem for short arcs

Approximation formulas are found for and , wherex(t) satisfies ,x(0)=x ₀,x(1)=x ₁. The results are applied to an example of two-body motion.     

TEMPORAL AND SPATIAL ASPECTS OF BLOWING DUST IN THE MOJAVE AND COLORADO DESERTS OF SOUTHERN CALIFORNIA, 1973–1994

Although dust storms rarely occur in southern California's deserts, blowing dust often reduces visibility, and large spatial and temporal variability in the frequency of blowing dust occurs throughout the region. On average only 1.3 dust storms occur in the study area each year. The annual average number of dust events (visibility <11 km) is 18.0, with the Coachella Valley being dustiest region, averaging 37.8 dust events each year. Mean annual frequencies of dust events for 1973–1994 are mapped, showing a core of activity centered over the Imperial/Coachella Valley region, with fewer dust events around the periphery of the study area. Most stations show a coherent temporal pattern of dust frequency during the period 1973–1994, with the mid-1970s experiencing the most dust. Blowing dust generally was absent from all stations during 1979–1983, 1987–1989, and 1992–1994. The mid-1980s were moderately dusty and 1990–1991 saw a return to very dusty conditions, possibly resulting from below-normal precipitation and increased anthropogenic disturbances. Dust events in the Mojave Desert characteristically occur during the winter to spring months (February-May), associated with dry frontal activity, and are largely absent during the dry summer months. The Colorado Desert experiences a similar seasonal distribution of dust events, but has more summer events, usually associated with convective thunderstorms. Frequencies of blowing dust have weak, but statistically significant, correlations with mean annual and antecedent precipitation, suggesting that complex processes control dust emission. [Key words: blowing dust, dust storms, Mojave Desert, Colorado Desert, wind erosion.]