Land use changes often lead to soil erosion, land degradation, and environmental deterioration. However, little is known about just how much humans accelerate erosion compared to natural background rates in non-agricultural settings, despite its importance to knowing the magnitude of soil degradation. The lack of understanding of anthropogenic acceleration is especially true for arid regions. Thus, we used ¹⁰Be catchment averaged denudation rates (CADRs) to obtain natural rates of soil erosion in and around the Phoenix metropolitan region, Arizona, United States. We then measured the acceleration of soil erosion by grazing, wildfire, and urban construction by comparing CADRs to erosion rates for the same watersheds, finding that: (i) grazing sometimes can increase sediment yields by up to 2.3–2.6x, (ii) human-set wildfires increased sediment yields by up to 9.7–10.4x, (iii) after some post-fire vegetation recovered, sediment yield was then up to 4.2–4.5x the background yield, (iv) construction increased sediment yields by up to 5.0–5.6x, and (v) the sealing of urban surfaces led to one-tenth to one-half of the background sediment yields. The acceleration of erosion at the urban–rural interface in arid lands highlights the need for sustainable management of arid-region soils.

Many rapidly urbanizing desert cities (RUDC) around the globe experience an acute risk of flooding. To reduce this risk, properly engineered flood control structures (FCS) must account for sediment accumulation as well as flood waters. While the Phoenix area, USA, uses regional data from non-urban, non-desert watersheds to generate sediment yield rates, the proposed desired outcome for RUDCs is to base FCS on data related to urbanization. Wolman (1967 Geogr. Ann. A 49 385–95) recognized that sediment yields spike during a relatively short period of bare-ground exposure associated with urban growth, followed by surface sealing resulting in a great reduction in sediment yield. This research presents a new analysis of empirical data where two regression models provide estimates of a more realistic sediment accumulation for arid regions and also urbanization of a desert cities: (i) linear regression between drainage area and sediment yield based on a compilation of more than 150 global sediment yield data for warm desert (BWh Köppen‐Geiger) climate; and (ii) linear regression relating percent urban growth with sediment yield using available data on urbanization-generated sediment associated with growth of a desert city. The new model can be used to predict the realistic sediment accumulation for helping provide data where few data exists in urbanizing parts of arid Africa, southwest Asia, and India.

Healthy soils are an essential ingredient of land systems and ongoing global change. Urbanization as a global change process often works through the lens of urban planning, which involves urban agriculture, urban greening, and leveraging nature-based solutions to promote resilient cities. Yet, urbanization frequently leads to soil erosion. Despite recognition of this tension, the rate at which the urban growth boundary accelerates soil erosion above natural background levels has not yet been determined. Our goal here is to provide a first broad estimate of urbanization’s impact of soil erosion. By combining data on modern erosion levels with techniques for estimating long-term natural erosion rates through cosmogenic nuclide ¹⁰Be analysis, we modeled the impact of urbanization on erosion across a range of cities in different global climates, revealing an acceleration of soil erosion ~7–19x in environments with mean annual precipitation <1500 mm; growth in wetter urban centers accelerated soil erosion ~23–72x. We tested our statistical model by comparing natural erosion rates to decades of monitoring soil erosion on the margins of Phoenix, USA. A century-long expansion of Phoenix accelerated soil erosion by ~12x, an estimate that is roughly at the mid-point of model projections for drier global cities. In addition to urban planning implications of being able to establish a baseline target of natural rates of soil erosion, our findings support the urban cycle of soil erosion theory for the two USA National Science Foundation urban long-term ecological research areas of Baltimore and Phoenix.