The Influence of Climate Change on River Corridors in Drylands: The Case of the Tehuacán-Cuicatlán Biosphere Reserve

The Tehuacán-Cuicatlán Biosphere Reserve, Mexico (TCBR) is the southernmost arid or semi-arid zone with the highest biodiversity in North America and is a UNESCO World Heritage site. Two main hydrographic streams cross the TCBR, the Salado River (an endogenous river) and the Grande River (an exogenous river). This study investigated temperature anomalies over the past 40 years. We analyzed potential differences between sub-basins and riparian areas on both streams using various indices, namely the Global Warming Index (GWI), Normalized Difference Vegetation Index (NDVI), Normalized Difference Water Index (NDWI), and Normalized Difference Drought Index (NDDI), and analyzed the potential relationship of these indices with climate change. Time series of satellite-based precipitation (June 2000–December 2020) and air temperature (January 1980–December 2020) were analyzed. A set of Landsat 8 OLI TIRS imagery from the driest and wettest months (2013–2020) was used to estimate NDVI, NDWI, and NDDI. These indices were evaluated separately for the sub-basins and river corridors in the dry and rainy seasons. The precipitation records indicate that in the Grande river sub-basin, precipitation is higher than in the Salado river sub basin. Normalized temperature anomalies and the GWI suggest a warming trend from 1994 to 2020, increasing up to 0.86°C in the Salado River and 0.52°C in the Grande River. The Grande and Salado sub basins showed significant differences between dry and wet seasons for each index (NDVI, NDWI, and NDDI). A Discriminant Analysis showed that the Salado sub-basin and the Salado River corridor are associated with severe drying conditions in the dry season (highest NDDI values). In the wet season, the Grande River corridor showed intermediate values of NDVI and NDWI but low values of NDDI. The Grande River corridor in the dry season was characterized by intermediate values of NDVI, NDWI, and NDDI. These river corridors provide environmental services in a trade-off with the stream and should be considered biodiversity hotspots. Due to the accentuated warming trend and the lowest precipitation, the Salado River sub-basin showed desertification signs associated with climate change. Both the Salado and the Grande River corridors showed resilience strategies to face climatic conditions.

Urban Rivers Corridors in the Don Catchment, UK: From Ignored, Ignoble and Industrial to Green, Seen and Celebrated

Research on urban rivers often seeks to find commonalities to advance knowledge of the effect of urbanisation on rivers, and rightly so. But it is important, also, to develop a complementary understanding of how urban rivers can be distinct, to facilitate a more nuanced view of concepts such as the ‘urban river syndrome’ and of the challenges facing those who wish to create more sustainable urban river corridors. To this end we use the Don Catchment as a case study to illustrate how historic patterns of urbanisation have been fundamental in shaping the catchment’s rivers. Following the Industrial Revolution, the catchment became an industrial centre, resulting in the ecological death of river ecosystems, and the disconnection of communities from stark urban river corridors. Widescale deindustrialisation in the 1970s and 1980s then resulted in a partial ecological recovery of the rivers, and ignited public interest. This history has imbued the catchment’s urban river corridors with a distinctive industrial character that can vary greatly between and within settlements. It has also left a legacy of particular issues, including a high degree of river habitat fragmentation and physical modification, and of negative perceptions of the rivers, which need improving to realise their potential as assets to local communities.

Rediscovering, Reevaluating, and Restoring Lost River-Wetland Corridors

River-wetland corridors form where a high degree of connectivity between the surface (rheic) and subsurface (hyporheic) components of streamflow creates an interconnected system of channels, wetlands, ponds, and lakes. River-wetland corridors occur where the valley floor is sufficiently wide to accommodate a laterally unconfined river planform that may feature morphologically complex, multi-threaded channels with vegetated bars, islands, and floodplains. River-wetland corridors can develop anywhere there is valley expansion along a drainage network, from the headwaters to estuaries or deltas, and they are found across all latitudes and within all biomes and hydroclimates. River-wetland corridors may be longitudinally continuous but are commonly interspersed with single-thread reaches in narrower portions of the valley. The development and persistence of river-wetland corridors is driven by combinations of geologic, biotic, and geomorphic processes that create a river environment that is diverse, heterogeneous, patchy, and dynamically stable, and within which patterns of flow, sediment features, and habitats shift continually. Hence, we describe these polydimensional river corridors as “kaleidoscope rivers.” Historically, river-wetland corridors were pervasive in wide, alluvial valley reaches, but their presence has been so diminished worldwide (due to a diverse range of anthropogenic activities and impacts) that the general public and even most river managers are unaware of their former pervasiveness. Here, we define river-wetland corridors as a river type; review paleoenvironmental and historical records to establish their past ubiquity; describe the geologic, biotic, and geomorphic processes responsible for their formation and persistence; and provide examples of river-wetland corridor remnants that still survive. We close by highlighting the significance of the diverse river functions supported by river-wetland corridors, the consequences of diminution and neglect of this river type, and the implications for river restoration.

Urban Design and Rivers: A Critical Review of Theories Devising Planning and Design Concepts to Define Riverside Urbanity

In a post-industrial world one of the foci of urbanism has been on the regeneration of former industrial sites along urban rivers. This is a contemporary urban design issue that needs further attention, especially in relation to urban forms and design interventions. This paper sets out to contribute to research in design by reviewing past theories and practices in order to inform the formation of conceptual ideas. These are of importance to inform practice and ensure responsive and responsible processes in planning and design. Such a review has hitherto been lacking, but with a renewed interest in urban densification, research in the design of cities is required. Thus, this paper provides a critical assessment of theories, which are identified and categorised in relation to urban riverside regeneration. For this study, urban design is considered as a craft requiring ‘savoir faire’ to ensure the functionality and quality of urban spaces. Transferable principles and ideas are identified in relation to the specific characteristics of riverside locations contributing to the definition of a ‘riverside urbanity’. It provides a theoretical framework identifying types of riverside landscapes, including the relationship between urban forms and river corridors.

Human–River Encounter Sites: Looking for Harmony between Humans and Nature in Cities

Human welfare depends on the health of nature. Decades of ill-conceived management practices caused a decline in the quality of human life, as well as in biological and cultural diversity. Simultaneously, they increased social and ecological risks. For instance, mismanagement of urban rivers jeopardizes their ecological health and ability to provide ecosystem services. While demands for responsible urban riverscape design that fulfill both human and ecosystem needs are increasing, explicit recommendations to achieve these ambitious goals are still lacking. We present a first attempt of a conceptualization of Human–River Encounter Sites for urban rivers that targets reconciliation between humans and nature within urban river corridors. It builds upon the River Culture Concept with literature reviews and experiences from river restoration projects. We identify six tenets that are important to develop guidelines for Human–River Encounter Sites: health, safety, functionality, accessibility, collaboration, and awareness. This paper presents how these tenets can collectively help to harmonize the needs of citizens and biota, and to mitigate the current urban river crisis. This contribution feeds the debate on sustainable socio-ecological management of urban rivers and provides guidelines for the implementation of future urban river restorations and management efforts.

Mapping river corridors at the network scale for integrating natural infrastructures into rural/urban spatial planning

<p>The “green infrastructure” metaphor have put a new emphasis on river spatial planning as a mean to protect fluvial corridors on the long term (Kline and Cahoon, 2010) as they provide ecosystem benefits such as flood expansion zones or better functioning ecological networks. In order to provide support data for strategic planning at the regional or national scales, we have developed automated mapping tools of fluvial corridors and floodplains based on high-resolution DEM and landcover datasets. Our goal is to characterize the continuity of fluvial corridors in the longitudinal and lateral dimensions and produce indicators on their integrity.</p><p>Following the work done by Alber and Piégay (2011) and Roux et al. (2015), we produced high-resolution detrended DEM (height maps) that support the delineation of valley bottoms, can be used for 0D flood risk mapping or to identify potential wetlands. Based on the hypothesis that fluvial processes imprint the modern landscape, even in the presence of human-driven disturbance, we have also developed a novel landcover continuity analysis method. These continuity maps provide insights on the spatial scale of river processes and the amount of space, if not natural, that is still well connected to the river and is eventually available for floodplain restoration. Finally, we explored the possibility to disseminate our results through a web platform to share the database across scales for promoting participative approaches and land use planning.</p><p>At the intersection between fluvial risks mitigation, water resource preservation, and biodiversity and landscape conservation, this strategy is rooted in the concept of “freedom of space” and unifies the concepts of greenways, waterways and floodways in a common approach to making room for the river and working with natural processes, integrating the concept of natural infrastructures that has been proposed in the 1990s (Mermet, 1993). This holistic view insists on river corridors and floodplains as multifunctional spaces. It is expected that this spatial knowledge will in turn raise awareness and encourage local authorities to better protect river corridors as green infrastructures through land planning.</p><p>Further perspectives include studying how the intended recipients of our approach, such as local authorities or river practitioners, appropriate the produced maps and information, and to what extent they contribute to an effective protection of river corridors. This understanding should prove useful to integrate such data into regional observatories and communicate a more integrative view of the river.</p>