Accurate delineation of drainage networks (DNs) is crucial for hydrological or hydraulic modelling, and the com-24 prehension of fluvial processes. This task presents challenging aspects in complex lowland terrains with subtle 25 relief and particularly for data poor-areas like the Cuvelai river basin (CRB), Namibia, where the present study 26 takes place. In the CRB standard methods of drainage network extraction from low resolution gridded digital 27 elevation models (DEMs) are unsuitable, hence airborne Light Detection and Ranging (LiDAR) solutions have 28 been utilized. However, LiDAR also presents challenges to large areal applications, especially with a surface 29 roughness exceeding the capacity of numerous algorithms. Indeed, LiDAR-based DEMs (2 and 50 m resolutions) 30 need to be hydrologically corrected and smoothed to enable the extraction of scale-relevant geomorphologic 31 features such as DNs. In the present contribution, channels from topographic maps (blue lines) were compared 32 to those from hydrologically corrected and uncorrected LiDAR DEMs, heads-up digitized channels from high-33 resolution digital aerial orthophotographs, field-mapped channels and auxiliary data. The 'maximum gradient 34 deterministic eight (D8)' GIS algorithm was applied to the corrected and uncorrected LiDAR DEMs using two 35 network extraction methods: area threshold support and curvature/drop analysis. Different progressive flow 36 accumulation threshold values (12) were used to delineate channels with these methods. Validation was per-37 formed between the field-mapped channels, the modelled channels and those derived from multiple sources. 38 Additionally, spatial and quantitative analyses were performed on geomorphologic parameters and indices.39 The results have shown that hydrologically corrected LiDAR DEMs offer useful details for identifying low order 40 stream segments in headwaters, while blue lines derived from the national hydrography datasets for watersheds, 41 located in elevated and low-lying areas of the study area, underestimated total stream lengths for field-mapped 42 channels by −15.3% and −88.5%, respectively. This study also confirmed that DNs can be extracted from com-43 plex low-terrain areas with standard GIS algorithms and accurate field data. The results will aid national mapping 44 agencies in data-poor regions to modernize their national hydrography datasets and to account for changing land 45 surface conditions that can affect channel spatial arrangements over time. Angola and Namibia (Fig. 1), encompasses these and many other 64 challenges related to flood risk management. 65The CRB, where this research has taken place, displays a series of
BackgroundEquitable access to health services is a key ingredient in reaching health for persons with disabilities and other vulnerable groups. So far, research on access to health services in low- and middle-income countries has largely relied on self-reported survey data. Realizing that there may be substantial discrepancies between perceived and actual access, other methods are needed for more precise knowledge to guide health policy and planning. The objective of this article is to describe and discuss an innovative methodological triangulation where statistical and spatial analysis of perceived distance and objective measures of access is combined with qualitative evidence.MethodsThe data for the study was drawn from a large household and individual questionnaire based survey carried out in Namibia and Malawi. The survey data was combined with spatial data of respondents and health facilities, key informant interviews and focus group discussions. To analyse access and barriers to access, a model is developed that takes into account both measured and perceived access. The geo-referenced survey data is used to establish four outcome categories of perceived and measured access as either good or poor. Combined with analyses of the terrain and the actual distance from where the respondents live to the health facility they go to, the data allows for categorising areas and respondents according to the four outcome categories. The four groups are subsequently analysed with respect to variation in individual characteristics and vulnerability factors. The qualitative component includes participatory map drawing and is used to gain further insight into the mechanisms behind the different combinations of perceived and actual access.ResultsPreliminary results show that there are substantial discrepancies between perceived and actual access to health services and the qualitative study provides insight into mechanisms behind such divergences.ConclusionThe novel combination of survey data, geographical data and qualitative data will generate a model on access to health services in poor contexts that will feed into efforts to improve access for the most vulnerable people in underserved areas.
Journeying from "I" to "we": Assembling hybrid caring collectives of geography doctoral scholars Completing a PhD is difficult. Within a city and a university recovering from a major earthquake sequence, general stress levels are much higher, and caring for some of the non-academic needs of doctoral scholars becomes critically important to these scholars' success. Yet in the same situation, academic supervisors may be stretched to the limits of their capacity to care even just for doctoral scholars' research training needs, let alone their broader pastoral care. The question, then, is how do we increase capacity to provide care for doctoral scholars in this kind of environment? While it has been shown elsewhere that supportive and interactive department cultures are correlated with lower attrition rates (Lovitts & Nelson, 2000), little work has been done on how exactly departments might go about in creating these supportive environments: the focus is generally on the individual actions of supervisors, or the individual quality and independence of students admitted (Johnson, Lee, & Green, 2000). In this article, we suggest that a range of actors and contingencies are involved in journeying toward a more caring collective culture. We direct attention to the hybridity of a "caring collective" emerging in the Department of Geography at the University of Canterbury. Following Callon and Rabeharisoa (2003), our caring collective is hybrid because the actors assembled are not only "students" and "staff", but also bodies, technologies, objects, institutions and other nonhuman actors including tectonic plates and earthquakes. The concept of the hybrid caring collective is useful, we argue, as a way of understanding the distributed responsibility for the care of doctoral scholars, and as a way of stepping beyond the student/supervisor blame game.
Worldwide, more than 40% of all natural hazards and about half of all deaths are the result of flood disasters. In northern Namibia flood disasters have increased dramatically over the past half-century, along with associated economic losses and fatalities. There is a growing concern to identify these extreme precipitation events that result in many hydro-meteorological disasters. This study presents an up to date and broad analysis of the trends of hydro-meteorological events using extreme daily precipitation indices, daily precipitation data from the Grootfontein rainfall station (1917–present), regionally averaged climatologies from the gauged gridded Climate Research Unit (CRU) product, archived disasters by global disaster databases, published disaster events in literature as well as events listed by Mendelsohn, Jarvis and Robertson (2013) for the data-sparse Cuvelai river basin (CRB). The listed events that have many missing data gaps were used to reference and validate results obtained from other sources in this study. A suite of ten climate change extreme precipitation indices derived from daily precipitation data (Grootfontein rainfall station), were calculated and analysed. The results in this study highlighted years that had major hydro-meteorological events during periods where no data are available. Furthermore, the results underlined decrease in both the annual precipitation as well as the annual total wet days of precipitation, whilst it found increases in the longest annual dry spell indicating more extreme dry seasons. These findings can help to improve flood risk management policies by providing timely information on historic hydro-meteorological hazard events that are essential for early warning and forecasting.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.