Quantification of vegetation effects on shallow landslide probability at regional scales

Shallow landslides are the cause of considerable direct and indirect losses to individuals, enterprises and society as a whole. An increase in shallow landslide occurrence is often related to the loss of the protective effect of trees by deforestation. Methods of targeted reforestation, such as silvopastoralism, can in turn reduce the risk associated with shallow landslides considerably. The effective implementation of such systems can benefit from guidance in terms of tree placement, planting density, planting pattern, tree species selection and tree size development prediction. For this guidance, computational models can help greatly, in addition to expert knowledge, especially on a regional scale. In this work a quantitative, physically-based, tool to assess the influence of vegetation on shallow landslide occurrence is presented. The focus is specifically on rainfall-induced translational shallow landslides on a regional scale. The results of this tool are ideally incorporated into holistic analyses of site-specific tree benefits and co-benefits. The tool as developed in this thesis is called SlideforMAP. It incorporates a probabilistic approach since the regional scale often poses challenges regarding heterogeneity in a range of parameters. Explicitly including this as uncertainty in the model can improve the model performance. Slope stability is computed by the limit equilibrium approach for a large number of randomly placed hypothetical landslide. The fraction of these hypothetical slides that are unstable, corresponds to local shallow landslide probability. The hydrological module is based on a topographic index and assumes a steady state sub-surface flux. All mechanical influences of vegetation are included with basal and lateral root reinforcement, being incorporated using the Root Bundle Model weibull approach on a single-tree basis. The model is calibrated and applied to three study areas (0.5 - 7.5 km2) in Switzerland. Tree density is 33 to 73 trees/ha on average, but all study areas consist of distinct forested and non-forested sections. Soil thickness, soil cohesion, and the ratio between precipitation intensity and hydraulic saturated conductivity are found to be the most sensitive model parameters. Performance is measured against a 2005 landslide inventory and the Receiver Operator Curve analysis. Area Under the Curve values are between 0.64 and 0.93. It is proven that the single-tree based inclusion of mechanical effects significantly improves model performance, as compared to a forest stand approach. To assess generalizability, SlideforMAP is applied in New Zealand silvopastoral systems in two small study areas (1.4 and 3.5 km2). Over these areas a full calibration and validation of SlideforMAP and an improved version of SlideforMAP is performed. The improved version includes interception, passive earth pressure, root compression, a non-steady state approach to the lateral flux and a runoff coefficient. The runoff coefficient is dependent on cumulative precipitation and relates tree presence to increased macropore presence and subsequently to an increased runoff coefficient. The availability of RADAR-based precipitation data enables a more realistic precipitation input by finding a representative rainfall intensity. The non-steady state approach, runoff coefficients, representative rainfall intensity and novelties. The inclusion of such novelties did not improve model performance, which could be due to flaws in its methodology, the performance measure or site-specific reasons. To place the application of SlideforMAP in context, it is compared to a statistical approach using binary logistical regression to shallow landslide susceptibility in New Zealand silvopastoral systems. For this a 2010 landslide inventory and a 2005 rainfall event are used. The model outputs are in agreement in approximately 70% of the study areas. Accountable for the remaining 30% are methodological differences, the heterogeneous input data in SlideforMAP and the difference in tree influence. SlideforMAP includes mechanical effects, where the statistical method implicitly includes all tree effects, but averaged over all trees. Practitioners are advised to prioritize tree planting on areas where both models are in agreement and predict high shallow landslide susceptiblity. SlideforMAP stands among other state of the art models focussed on vegetation effects on shallow landslide activity. This is due to the inclusion of single tree based lateral and basal root reinforcement and the tailoring to specific rainfall events. Further developments in SlideforMAP have enabled the application on large scales and for the analyses of specific components. All in all, land managers can benefit greatly by applying SlideforMAP to find the ideal targeted planting sites and stabilize the soil, as efficient as possible from a cost-benefit standpoint

Detection of H_2 Pure Rotational Line Emission from the GG Tauri Binary System

We present the first detection of the low-lying pure rotational emission lines of H_2 from circumstellar disks around T Tauri stars, using the Short Wavelength Spectrometer on the Infrared Space Observatory. These lines provide a direct measure of the total amount of warm molecular gas in disks. The J = 2 → 0 S(0) line at 28.218 μm and the J = 3 → 1 S(1) line at 17.035 μm have been observed toward the double binary system GG Tau. Together with limits on the J = 5 → 3 S(3) and J = 7 → 5 S(5) lines, the data suggest the presence of gas at T_(kin) ≈ 110 ± 10 K with a mass of (3.6 ± 2.0) × 10^(-3) M_☉ (±3 σ). This amounts to ~3% of the total gas + dust mass of the circumbinary disk as imaged by millimeter interferometry, but it is larger than the estimated mass of the circumstellar disk(s). Possible origins for the warm gas seen in H_2 are discussed in terms of photon and wind-shock heating mechanisms of the circumbinary material, and comparisons with model calculations are made

Interferometric Observations of Formaldehyde in the Protoplanetary Disk around LkCa15

Emission from the $2_{12}-1_{11}$ line of H$_2$CO has been detected and marginally resolved toward LkCa15 by the Nobeyama Millimeter Array. The column density of H$_2$CO is higher than that observed in DM Tau and than predicted by theoretical models of disk chemistry; also the line-intensity profile is less centrally peaked than that for CO. A similar behavior is observed in other organic gaseous molecules in the LkCa 15 disk.Comment: 5 pages, 4 figures. accepted to PASJ (Publication of Astronomical Society of Japan

The gas temperature in flaring disks around pre-main sequence stars

A model is presented which calculates the gas temperature and chemistry in the surface layers of flaring circumstellar disks using a code developed for photon-dominated regions. Special attention is given to the influence of dust settling. It is found that the gas temperature exceeds the dust temperature by up to several hundreds of Kelvins in the part of the disk that is optically thin to ultraviolet radiation, indicating that the common assumption that Tgas=Tdust is not valid throughout the disk. In the optically thick part, gas and dust are strongly coupled and the gas temperature equals the dust temperature. Dust settling has little effect on the chemistry in the disk, but increases the amount of hot gas deeper in the disk. The effects of the higher gas temperature on several emission lines arising in the surface layer are examined. The higher gas temperatures increase the intensities of molecular and fine-structure lines by up to an order of magnitude, and can also have an important effect on the line shapes.Comment: 14 pages, 10 figures, accepted for publication in A&

How Is Context Addressed in Growth Monitoring? A Comparison of the Tanzanian, Indian, and Dutch Manuals

BACKGROUND: To address malnutrition in all its forms, context should be taken into account in growth-monitoring (GM) practices. OBJECTIVES: The aim was to compare GM manuals of countries with different nutrition problems, and to assess how these manuals are adapted to the different biological, socioeconomic, and cultural contexts. METHODS: GM manuals from Tanzania, India, and the Netherlands were compared with each other, and with the materials for the WHO training course on child growth assessment. First, the aims of GM, growth measurements, interpretation of these measurements, and counseling approaches are compared. Second, contextual determinants of malnutrition are identified using the UNICEF framework for malnutrition as an analytical model. RESULTS: Our results show that the GM manuals differ in their descriptions of the aim of GM, growth measurements, their interpretation, and counseling approaches. Assessing normal growth and detecting growth problems are among the aims of GM in all of the analyzed countries. In Tanzania and India, the focus is mainly on undernutrition, whereas the Dutch manuals focus on overweight and on underlying pathologies that contribute to poor linear growth. The findings of our analysis of contextual factors within the UNICEF framework show that the Tanzanian protocol is only minimally adapted to the local context. Of the manuals examined in our study, the Indian manual is most focused on the contextual determinants of malnutrition, and stresses the importance of taking customs and beliefs into account. The Dutch protocol, by contrast, emphasizes the importance of the biological environment, including parental height and ethnicity, as determinants of child growth. CONCLUSIONS: The country manuals we analyzed only partly reflect the contexts in which children live. To address malnutrition in all its forms, the GM manuals should take children's biological, socioeconomic, and cultural contexts into account, as this would help health professionals to tailor counseling messages for parents

Warm Molecular Layers in Protoplanetary Disks

We have investigated molecular distributions in protoplanetary disks, adopting a disk model with a temperature gradient in the vertical direction. The model produces sufficiently high abundances of gaseous CO and HCO+ to account for line observations of T Tauri stars using a sticking probability of unity and without assuming any non-thermal desorption. In regions of radius R > 10 AU, with which we are concerned, the temperature increases with increasing height from the midplane. In a warm intermediate layer, there are significant amounts of gaseous molecules owing to thermal desorption and efficient shielding of ultraviolet radiation by the flared disk. The column densities of HCN, CN, CS, H2CO, HNC and HCO+ obtained from our model are in good agreement with the observations of DM Tau, but are smaller than those of LkCa15. Molecular line profiles from our disk models are calculated using a 2-dimensional non-local-thermal-equilibrium (NLTE) molecular-line radiative transfer code for a direct comparison with observations. Deuterated species are included in our chemical model. The molecular D/H ratios in the model are in reasonable agreement with those observed in protoplanetary disks.Comment: 11 pages, Latex (aa.cls), to be published in Astronomy and Astrophysic

Detection of DCO+ in a circumstellar disk

We report the first detection of DCO+ in a circumstellar disk. The DCO+ J=5-4 line at 360.169 GHz is observed with the 15m James Clerk Maxwell Telescope in the disk around the pre-main sequence star TW Hya. Together with measurements of the HCO+ and H13CO+ J=4-3 lines, this allows an accurate determination of the DCO+/HCO+ ratio in this disk. The inferred value of 0.035+-0.015 is close to that found in cold pre-stellar cores and is somewhat higher than that measured in the envelope around the low-mass protostar IRAS 16293 -2422. It is also close to the DCN/HCN ratio obtained for pristine cometary material in the jet of comet Hale-Bopp. The observed DCO+/HCO+ ratio for TW Hya is consistent with theoretical models of disks which consider gas-phase fractionation processes within a realistic 2-D temperature distribution and which include the effects of freeze-out onto grains

Organic molecules in protoplanetary disks around TTauri and HerbigAe stars

The results of single-dish observations of low- and high-J transitions of selected molecules from protoplanetary disks around two TTauri stars (LkCa15 and TWHya) and two HerbigAe stars (HD163296 and MWC480) are reported. Simple molecules such as CO, 13CO, HCO+, CN and HCN are detected. Several lines of H2CO are found toward the TTauri star LkCa15 but not in other objects. No CH3OH has been detected down to abundances of 10E-9 - 10E-8 with respect to H2. SO and CS lines have been searched for without success. Line ratios indicate that the molecular emission arises from dense 10E6 - 10E8 cm-3 and moderately warm (T ~ 20-40K) intermediate height regions of the disk atmosphere, in accordance with predictions from models of the chemistry in disks. The abundances of most species are lower than in the envelope around the solar-mass protostar IRAS 16293-2422. Freeze-out and photodissociation are likely causes of the depletion. DCO+ is detected toward TWHya, but not in other objects. The high inferred DCO+/HCO+ ratio of ~0.035 is consistent with models of the deuterium fractionation in disks which include strong depletion of CO. The inferred ionization fraction in the intermediate height regions as deduced from HCO+ is at least 10E-11 - 10E-10, comparable to that derived for the midplane from recent H2D+ observations. (abridged abstract)Comment: Accepted for publication in A&A. 21 pages, 6 figures Tables 3, 4, 5 will only be published in the electronic version of the Journa

Detection of H2 pure rotational line emission from the GG~Tau binary system

We present the first detection of the low-lying pure rotational emission lines of H2 from circumstellar disks around T~Tauri stars, using the Short Wavelength Spectrometer on the Infrared Space Observatory. These lines provide a direct measure of the total amount of warm molecular gas in disks. The J=2->0 S(0) line at 28.218 mum and the J=3->1 S(1) line at 17.035 mum have been observed toward the double binary system GG Tau. Together with limits on the J=5->3 S(3) and J=7->5 S(5) lines, the data suggest the presence of gas at T_kin=110+-10 K with a mass of (3.6+-2.0)x10^-3 M_sol (3sigma). This amounts to ~3% of the total gas + dust mass of the circumbinary disk as imaged by millimeter interferometry, but is larger than the estimated mass of the circumstellar disk(s). Possible origins for the warm gas seen in H2 are discussed in terms of photon and wind-shock heating mechanisms of the circumbinary material, and comparisons with model calculations are made.Comment: 14 pages including 1 figure. To appear in Astrophysical Journal Letter