Progress in Physical Geography: Earth and Environment

Although agricultural influence on sediment runoff is well known, determining what sources of sediment contribute most to stream impairment has remained challenging in agricultural watersheds across the world. Therefore, methods to distinguish the sources of sediment in streams are warranted, particularly methods that incorporate information on anthropogenic practices that affect sediment runoff. In this study we examined how variations in conservation practices contributed to unidentified sources of sediment in an agricultural watershed, where 49% of sediment was sourced from agricultural fields that were assumed to have little erosional runoff. We found that variations in the way no-till agriculture is practiced significantly affected estimates of erosion in the watershed and also led agency managers to overlook sources of sediment in the watershed. In doing this research, we provide a methodological framework that may be useful to researchers who are attempting to identify sources of sediment erosion in watersheds impacted by variations in agricultural conservation practices.

Utilizing solar energy requires accurate information about global solar radiation (GSR), which is critical for designers and manufacturers of solar energy systems and equipment. This study aims to examine the literature gaps by evaluating recent predictive models and categorizing them into various groups depending on the input parameters, and comprehensively collect the methods for classifying China into solar zones. The selected groups of models include those that use sunshine duration, temperature, dew-point temperature, precipitation, fog, cloud cover, day of the year, and different meteorological parameters (complex models). 220 empirical models are analyzed for estimating the GSR on a horizontal surface in China. Additionally, the most accurate models from the literature are summarized for 115 locations in China and are distributed into the above categories with the corresponding solar zone; the ideal models from each category and each solar zone are identified. Comments on two important temperature-based models that are presented in this work can help the researchers and readers to be unconfused when reading the literature of these models and cite them in a correct method in future studies. Machine learning techniques exhibit performance GSR estimation better than empirical models; however, the computational cost and complexity should be considered at choosing and applying these techniques. The models and model categories in this study, according to the key input parameters at the corresponding location and solar zone, are helpful to researchers as well as to designers and engineers of solar energy systems and equipment.

Beaver canals and their environmental effects are much less studied than beaver dams, despite being widespread in some beaver-inhabited areas. In this study, we completed a systematic review of previous research on the structure and ecosystem effects of beaver canals to provide an increasingly holistic understanding of these landscape features. Specifically, we: 1) summarized why, where, when, and how beaver develop canals; 2) chronicled all published descriptions on beaver canal morphology; and 3) summarized the literature on the environmental effects of beaver canals. Thirty-one relevant studies were identified and incorporated into this review. Beaver canals have been identified in numerous environments ranging from largely undeveloped mountainous regions to heavily developed agricultural landscapes. Beaver primarily develop canals to increase accessibility to riparian resources, facilitate transport of harvested resources, and to decrease predation risk. As with beaver dams, beaver canals exhibit large structural variability, particularly in lengths, which can be over 0.5 km. Widths of about 1 m and depths of about 0.5 m are common. Beaver canals alter watershed hydrology by creating new aquatic habitats, connecting isolated aquatic features, and diverting water into colonized areas. Beaver canals have been identified as favored habitats for several biotic species and are sometimes used during critical life stages (e.g. dispersal). In addition to increasing overall floral and faunal species richness and diversity, beaver canals may benefit biota by mitigating habitat fragmentation and climate change impacts. Based on the results of this review, incorporating beaver canals into stream restoration practices may be environmentally beneficial.

Climate models project increased extreme precipitation for the coming decades, which may lead to higher soil erosion in many locations worldwide. Different soil erosion model concepts are used to assess the impact of climate change on soil erosion at large spatial scales, including models forced by precipitation and by runoff. However, there is little knowledge of the implications of soil erosion model conceptualization on projected soil erosion rates under climate change. Here, we assess the impact of climate change with the three most widely used soil erosion model concepts: a model forced by precipitation (RUSLE); a model forced by runoff (MUSLE); and a model forced by precipitation and runoff (MMF). We applied the models to two contrasting Mediterranean catchments (south-east Spain), where climate change is projected to decrease the annual precipitation sum and increase extreme precipitation, based on the RCP8.5 climate change scenario. Depending on the model, soil erosion is projected to decrease (RUSLE) or increase (MUSLE and MMF) in the study area. Although it is difficult to validate future model projections, the differences between the model projections are, inherently, a result of their model conceptualization: a decrease in soil loss due to a decrease in the annual precipitation sum (RUSLE); and an increase in soil loss due to an increase in extreme precipitation and, consequently, increased runoff (MUSLE). An intermediate result is obtained with MMF, in which a projected decrease in detachment by raindrop impact is counteracted by a projected increase in detachment by runoff. We conclude that in climate change impact assessments it is important to select a soil erosion model that is forced by both precipitation and runoff, which under climate change may have a contrasting effect on soil erosion.

Exploring prehistoric variation in human–environmental interaction is critical for understanding the historical patterns and mechanisms of long-term human–land evolution. In this paper we review the published radiocarbon and optically stimulated luminescence (OSL) data from Late Paleolithic, Neolithic and Bronze Age sites in China, analyze the spatial–temporal distribution of these sites, and compare it with the results of recent paleoclimatic and archaeological studies. We seek to study the trajectory and influencing factors of human–environmental interactions in late prehistoric China. We detect changing patterns in the relationship between humans and the environment during different phases of the prehistoric era in China. Climate change clearly affected the environment of hunter-gatherer groups between 50,000–10,000 BP (before present, defined as 1950AD), and variation in human population in Neolithic China (∼10,000–4000 BP) was likely influenced primarily by the development of agriculture, in addition to substantial climate events. The spatial scale of human settlements expanded in the Bronze Age (∼4000–2200 BP) in a period of cooling climate. During this time the impact of human activities on the environment increased significantly, primarily caused by technological innovations related to the onset of prehistoric transcontinental cultural exchange in Eurasia.

Soil and water conservation (SWC) interventions are needed to control rainfall-driven erosion, and profitability of SWC measures at the sub-catchment scale emerges as the principal reason for their adoption. This study carried out a cost–benefit analysis of SWC measures in mountainous agricultural catchments. Physical data were obtained through field measurements of discharge, sediment and nutrient loss at the sub-catchment scale with and without SWC measures. The major cost benefits of various measures implemented in the study area were quantified using net present value (NPV), and direct market prices were employed in valuing the cost of items required for crop production. The results revealed that sediment loss decreased by 8.78 Mg ha⁻¹ y⁻¹ (46.8%) due to SWC measures, and the cost of production inputs, such as fertilizer (urea) and lime, was reduced by $17.97 ha⁻¹ y⁻¹ and $3.63 ha⁻¹ y⁻¹, respectively. Furthermore, crop yield was enhanced by 13% for teff, 19.4% for sorghum and 19.42% for chickpeas, which is equivalent to economic returns of $102, $96.9 and $140.25 ha⁻¹ y⁻¹, respectively. The total discounted cost of SWC interventions was about $331.74. This includes establishment costs, maintenance costs, input costs and the costs resulting from lost productive land. In sum, the total discounted benefits of SWC measures were the enhancement of crop production, a reduction in lime requirement and a reduction in the loss of total nitrogen and sediment, estimated at about $809.42. Hence, it is possible to deduce that SWC measures reduced nutrient depletion and greatly improved crop yield with a NPV of $477.68 ha⁻¹. The results strongly suggest that SWC measures in the study sub-catchment, as well as in nearby areas with a similar indigenous SWC adoption strategy, topographic conditions and agroclimatic characteristics, should be maintained.

Hazards often do not occur in isolation and, for this reason, a multi-hazard approach is vital in realising their impact and providing solutions for disaster risk reduction and sustainable development. We present a novel framework that emerges from a bibliometric analysis of the multi-hazard literature and a critical appraisal of the existing approaches. It was found that multi-hazard research has expanded greatly over the last 20 years, furthering our understanding of the subject with important applications in risk assessment and management. These studies have contextualised multi-hazards, developed models and frameworks to analyse them, provided case studies to test multi-hazard-based approaches and produced reviews. It was found that landslides and floods are the most frequently co-occurring hazards within the bibliographic dataset, yet understanding of their interactions, hydrometeorological drivers and landscape controls remains poorly conceptualised. Therefore, we propose a new framework for investigating water-related multi-hazards that leverages and synthesises existing methods to address the challenges identified to date. We also find a geographical bias, with less multi-hazard research in lower- and middle-income countries and remote environments due to data scarcity and limited accessibility. Our framework therefore includes the ability to address geographically specific key considerations including available and accessible data, community variability and cross-sectoral collaborations. In doing so it offers guidance on structuring future analyses to improve our understanding of multi-hazards, reduce disaster risk, increase community resilience and make progress towards sustainable development.

Rexford Daubenmire’s 1954 seminal review of alpine timberline in North America remains a valuable classic for timberline scholars. His article was published at a formative time for timberline studies and, as such, has affected the direction of timberline research for nearly 70 years. Daubenmire’s definition of timberline, his review of climatological theories controlling timberline, and his additions to altitudinal variations of timberline across latitudes remain at the forefront of timberline research.