Fire effects on soil and hydrology

Fire can significantly increase a landscape’s vulnerability to flooding and erosion events. By removing vegetation, changing soil properties and inducing soil water repellency, fire can increase the risk and erosivity of overland flow. Mitigation of land degradation and flooding events after fire can help safeguard natural resources and prevent further economical and ecological havoc, but can benefit from an improved understanding of its drivers. The aim of this thesis is to improve the understanding of the effects of fire on soil and hydrology. Laboratory and field studies focus on the relation between fire, soil, vegetation and hydrology as well as the effects of scale, in order to find the drivers of post-fire flooding and erosion events. The effect of soil heating on soil physical properties is evaluated, and the above- and belowground drivers of soil heating are investigated. Furthermore, the results of a unique field experiment are presented in which the Portuguese Valtorto catchment was burned by experimental fire. The effects of fire on soil and surface properties is assessed, as well as the changes in the temporal evolution of soil water repellency, Finally, the hydrological implications are discussed. The thesis concludes with recommendations for mitigation of fire-induced land degradation; focusing on guidelines for prescribed burns, that are used to prevent fire, and on reducing runoff and erosion in burned lands where fire prevention was unsuccessful. </p

Waterwinning voor beregening in de landbouw en op sportvelden: een overzicht van de regelgeving in Nederland

Dit rapport geeft een overzicht van de regelgeving voor het onttrekken van grond- en oppervlaktewater voor beregening in de landbouw en op natuurlijke sportvelden. De relevante wet- en regelgeving wordt besproken, en meld-, meet- en vergunningplichten evenals bijkomende kosten worden gegeven per provincie en waterschap. Zowel de regels voor als de kosten van onttrekkingen variëren sterk binnen Nederland, wat in sommige situaties leidt tot ogenschijnlijke willekeur en rechtsongelijkheid. Daarnaast is de huidige regelgeving in een aantal gevallen onduidelijk en onvindbaar. Harmonisatie van regelgevingen en kosten is noodzakelijk om te komen tot een helder, uniform en volledig beleid m.b.t grond- en oppervlaktewateronttrekkingen. Omdat de huidige informatievoorziening soms sterk te wensen overlaat zal deze harmonisatieslag gepaard moeten gaan met een verbeterde communicatie naar de gebruiker toe

Flooded by jargon: how the interpretation of water-related terms differs between hydrology experts and the general audience

Communication about hydrology-induced hazards is important, in order to keep the impact of floods, droughts et cetera as low as possible. However, sometimes the boundary between specialized and non-specialized language can be vague. Therefore, a close scrutiny of the use of hydrological vocabulary by both experts and laypeople is necessary. In this study, we compare the expert and lay definitions of 12 common water-related terms and 10 water-related pictures to see where misunderstandings might arise both in text and pictures. Our primary objective is to analyze the degree of agreement between experts and laypeople in their definition of the used terms. In this way, we hope to contribute to improving the communication between these groups in the future. Our study was based on a survey completed by 34 experts and 119 laypeople. Especially concerning the definition of water-related words there are some profound differences between experts and laypeople: words like river and river basin turn out to have a thoroughly different interpretation between the two groups. Concerning the pictures, there is much more agreement between the groups

Hydrological response of a small catchment burned by experimental fire

Fire can considerably change hydrological processes, increasing the risk of extreme flooding and erosion events. Although hydrological processes are largely affected by scale, catchment-scale studies on the hydrological impact of fire in Europe are scarce, and nested approaches are rarely used. We performed a catchment-scale experimental fire to improve insight into the drivers of fire impact on hydrology. In north-central Portugal, rainfall, canopy interception, streamflow and soil moisture were monitored in small shrub-covered paired catchments pre- and post-fire. The shrub cover was medium dense to dense (44 to 84 %) and pre-fire canopy interception was on average 48.7% of total rainfall. Fire increased streamflow volumes 1.6 times more than predicted, resulting in increased runoff coefficients and changed rainfall-streamflow relationships - although the increase in streamflow per unit rainfall was only significant at the subcatchment-scale. Fire also fastened the response of topsoil moisture to rainfall from 2.7 to 2.1 h (p = 0.058), and caused more rapid drying of topsoils after rain events. Since soil physical changes due to fire were not apparent, we suggest that changes resulting from vegetation removal played an important role in increasing streamflow after fire. Results stress that fire impact on hydrology is largely affected by scale, highlight the hydrological impact of fire on small scales, and emphasize the risk of overestimating fire impact when upscaling plot-scale studies to the catchment-scale. Finally, they increase understanding of the processes contributing to post-fire flooding and erosion events

Theory of charge transport in diffusive normal metal / unconventional singlet superconductor contacts

We analyze the transport properties of contacts between unconventional superconductor and normal diffusive metal in the framework of the extended circuit theory. We obtain a general boundary condition for the Keldysh-Nambu Green's functions at the interface that is valid for arbitrary transparencies of the interface. This allows us to investigate the voltage-dependent conductance (conductance spectrum) of a diffusive normal metal (DN)/ unconventional singlet superconductor junction in both ballistic and diffusive cases. For d-wave superconductor, we calculate conductance spectra numerically for different orientations of the junctions, resistances, Thouless energies in DN, and transparencies of the interface. We demonstrate that conductance spectra exhibit a variety of features including a $V$-shaped gap-like structure, zero bias conductance peak (ZBCP) and zero bias conductance dip (ZBCD). We show that two distinct mechanisms: (i) coherent Andreev reflection (CAR) in DN and (ii) formation of midgap Andreev bound state (MABS) at the interface of d-wave superconductors, are responsible for ZBCP, their relative importance being dependent on the angle $\alpha$ between the interface normal and the crystal axis of d-wave superconductors. For $\alpha=0$, the ZBCP is due to CAR in the junctions of low transparency with small Thouless energies, this is similar to the case of diffusive normal metal / insulator /s-wave superconductor junctions. With increase of $\alpha$ from zero to $\pi/4$, the MABS contribution to ZBCP becomes more prominent and the effect of CAR is gradually suppressed. Such complex spectral features shall be observable in conductance spectra of realistic high-$T_c$ junctions at very low temperature

Theory of charge transport in diffusive normal metal / conventional superconductor point contacts

Tunneling conductance in diffusive normal metal / insulator / s-wave superconductor (DN/I/S) junctions is calculated for various situations by changing the magnitudes of the resistance and Thouless energy in DN and the transparency of the insulating barrier. The generalized boundary condition introduced by Yu. Nazarov [Superlattices and Microstructures 25 1221 (1999)] is applied, where the ballistic theory by Blonder Tinkham and Klapwijk (BTK) and the diffusive theory by Volkov Zaitsev and Klapwijk based on the boundary condition of Kupriyanov and Lukichev (KL) are naturally reproduced. It is shown that the proximity effect can enhance (reduce) the tunneling conductance for junctions with a low (high) transparency. A wide variety of dependencies of tunneling conductance on voltage bias is demonstrated including a $U$-shaped gap like structure, a zero bias conductance peak (ZBCP) and a zero bias conductance dip (ZBCD)

Zwaarste in 30 jaar, minder regen, meer bosbranden in Australië

De toename van bosbranden in Australië welk effect heeft dit op de natuur