Infiltration rate, defined as the rate at which water enters the soil, is a fundamental parameter in flood management [1]. It influences soil moisture, groundwater recharge, and surface runoff, thereby playing a significant role in stormwater management [2]. Soils with high infiltration rates absorb larger volumes of rainwater, which helps reduce both the frequency and intensity of local flooding, lessens stormwater runoff volumes that burden urban drainage systems, and enhances groundwater recharge [3]. Understanding soil infiltration is essential for effective flood management, sustainable water resource management, and maintaining overall environmental health, particularly in flood-prone areas [4].

Urbanization typically disrupts natural hydrological processes by significantly increasing impervious surfaces (e.g., roads, buildings, parking lots [5]. This alteration often results in increased surface runoff volumes and peak flows, reduced groundwater recharge, and consequently heightened flood risks, alongside degraded water quality [6]. Urban parks, as essential components of green infrastructure, play a crucial role in mitigating these adverse effects by providing permeable surfaces that promote water infiltration, decrease runoff, and enhance water quality. However, their effectiveness in delivering these vital ecosystem services varies significantly based on several interconnected factors, particularly the soil’s infiltration characteristics [7][8].

Vegetation cover, land use, park maintenance, and site layout all significantly affect the rate of water absorbed by the soil, which greatly influences groundwater recharge, flood control, and ecosystem health [9]. For example, trees, significantly enhances the soil’s capacity to absorb water. Tree roots improve porosity and boost infiltration rates. Plant canopies also intercept rainfall, slowing down rain-drops and lessening their impact on the soil surface [10]. Land use directly influences water infiltration. In natural settings, such as forests and grasslands, most rainfall seeps into the soil, supporting consistent streamflow and maintaining good water quality [11]. The design and layout of cities greatly influence stormwater management. Impervious surfaces significantly disrupt the water cycle. They reduce water penetration into the ground [12]. Park maintenance practices can greatly affect soil infiltration rates. Regular maintenance can improve infiltration, while a lack of maintenance may cause rates to decline [13]. Although these are essential factors, the focus of the current study is to investigate the effect of soil on infiltration.

The infiltration rate in any given landscape, including urban parks, results from a complex interplay of factors [14]. These factors include soil texture (the relative proportions of sand, silt, and clay), soil structure (the arrangement of soil particles), organic matter content, antecedent soil moisture, and the degree of soil compaction [15]. Soil compaction, often caused by intensive recreational use, foot traffic, or construction and maintenance activities, can impact infiltration capacity, even in otherwise permeable soils. Additionally, vegetation cover and type significantly influence infiltration by maintaining soil structure, protecting the soil surface from raindrop impact, and creating macropores through their root systems [16]. In arid or semi-arid regions, such as Tucson, Arizona, characterized by low average annual precipitation that typically arrives in intense, short-duration storm events, effective management of soil infiltration is particularly crucial [17]. These areas face challenges related to water scarcity as well as risks of flash flooding. Tucson’s geological landscape features a diverse range of soil types; some regions have sandy or loamy soils that naturally exhibit higher infiltration rates, while others consist predominantly of clayey soils, which have inherently lower infiltration capacities [17].

Optimizing the infiltration potential of urban green spaces in these climates is vital for water conservation, reducing flood risk, and enhancing urban resilience to climate variability. While the importance of soil infiltration in urban ecosystems, especially in arid-region green spaces, is acknowledged, there has been a notable lack of comprehensive site-specific studies investigating these rates across various urban parks in Tucson. The current study aims to fill the knowledge gap. By examining the infiltration rates and capacities of different soil types found in selected urban parks in Tucson, AZ, this research provides valuable, evidence-based insights that will enhance urban park management, inform targeted stormwater management strategies, and guide park maintenance practices in Tucson and other arid cities.

Soil infiltration rates measured across the twelve urban parks sampled in Tucson are shown in Table 1. The rates varied significantly, ranging from a low of 0.69 mm/s to a high of 1.56 mm/s. This notable variation was strongly influenced by the soil type identified at each park location, with statistically significant differences observed among the soil types.

Table 1. Soil type and mean infiltration rates in sampled urban parks in Tucson, AZ.

The findings of this study show significant variability in soil infiltration rates across various urban parks in Tucson, Arizona, ranging from approximately 0.69 mm/s to 1.56 mm/s. This broad range highlights the considerable influence of soil type on infiltration capacity, even within managed urban green spaces. The differences are significant in arid or semi-arid regions, such as Tucson, where effective water resource management and stormwater mitigation are vital due to limited water supplies and the potential for intense rainfall events.

Parks with higher infiltration rates, such as La Madera Park (sandy loam) and Tahoe Park (silty sand), are significantly more effective at absorbing rainfall. This capacity enables better local stormwater runoff mitigation, potentially reducing the risk of localized urban flooding and alleviating the burden on municipal stormwater systems. Moreover, enhanced infiltration in these parks can contribute more meaningfully to groundwater recharge, a vital ecosystem service, particularly in water-scarce regions. For instance, a high-intensity, short-duration Tucson thunderstorm delivering 25 mm of rain in 30 minutes (an intensity of 50 mm/hr) would be largely or entirely infiltrated by the soils in La Madera or Tahoe parks, assuming no surface sealing or extreme antecedent moisture.

Conversely, parks with lower infiltration rates, such as Mirasol Park (silty clay + 0.69 mm/s), Augie Acuna Park (silty clay, 0.70 mm/s), and John F. Kennedy Park (silty clay), are more likely to produce surface runoff during heavy rainfall events. Even the 50 mm/hr storm intensity in the previous example would exceed the infiltration capacity of these soils, leading to ponding or runoff. These areas may require specific landscape design considerations or additional stormwater management strategies to enhance their ability to manage water and mitigate potential flood risks. Such strategies might include constructing rain gardens or bioswales in or near these parks, utilizing permeable surfaces and pavements in nearby pathways or parking areas, or applying targeted soil amendments to improve soil structure and porosity. The results strongly emphasize the need to incorporate soil-specific considerations into urban planning and the management of urban green infrastructure. A quantitative understanding of the infiltration characteristics of park soils enables urban planners, landscape architects, and park managers to make more informed decisions regarding irrigation scheduling (avoiding over-irrigation and runoff in low-infiltration areas), vegetation selection (choosing plants suited to soil moisture conditions and those that can enhance infiltration), and the implementation of best management practices (BMPs) aimed at maintaining or improving soil health and hydrological function. For instance, in parks with compacted soils or those dominated by clay, such as Mirasol or Augie Acuna, practices like core aeration, deep soil mixing, or incorporating organic matter (e.g., compost) could be beneficial for enhancing soil structure and, consequently, infiltration rates. Research has shown that organic matter amendments can significantly improve the hydraulic properties of clayey soils [22].

While soil texture emerged as a primary determinant, other factors likely contribute to variability in infiltration. Soil compaction from foot traffic, sports activities, or the use of maintenance vehicles can significantly reduce infiltration rates, regardless of texture [23]. Although not quantitatively measured in this study, observations in heavily used areas of parks suggest that compaction may lead to lower rates in certain zones. Vegetation type and density also play a role; well-established turf or native vegetation with extensive root systems can enhance infiltration compared to bare soil or sparsely vegetated areas [24].

This study effectively characterized and quantified soil infiltration rates across twelve urban parks in Tucson, AZ, revealing significant variations directly linked to soil textural properties. Sandy loam and silty sand soils exhibited the highest infiltration capacities, while silty clay and sandy clay soils recorded substantially lower rates (Table 1). These findings have critical implications for urban planning, stormwater management, park design, and maintenance strategies in Tucson and other cities confronting similar arid environmental conditions and water management challenges. Understanding these site-specific soil hydraulic properties is essential for designing resilient urban landscapes that can effectively manage stormwater, promote groundwater recharge, and contribute to sustainable water resource management in water-limited environments. This research provides an empirical basis for developing evidence-based approaches to optimize the hydrological performance of urban parks, thereby fostering more sustainable and resilient urban ecosystems that can adapt to changing climatic conditions.

This information provides essential, site-specific insights for enhancing urban planning and developing targeted stormwater management strategies, optimizing irrigation practices, and improving park maintenance to enhance soil health and hydrological function in Tucson and similar arid or semi-arid urban landscapes.

Based on the findings of this study, the authors recommend the following in Tucson and similar arid or semi-arid urban areas:

1) Integrate Soil Data into Planning and Design: Utilize soil infiltration data as a key input in the design and master planning of new urban parks, as well as the retrofitting of existing ones. Prioritize designs that protect and enhance infiltration in high-potential areas and incorporate engineered solutions (e.g., rain gardens, bioswales in with low infiltration.

2) Implement Soil-Specific Management Practices: Develop and implement park maintenance plans tailored to specific soil conditions. For parks with low-infiltration soils (e.g., Mirasol, Augie Acuna):

Minimize soil compaction through designated pathways, restricted vehicle access, and periodic aeration or soil amendment with organic matter Select drought-tolerant vegetation adapted to heavier soils and potentially periodic wetness if surface ponding occurs.

By adopting these recommendations, cities like Tucson can more effectively leverage their urban green spaces to manage stormwater, conserve water, and build more resilient and sustainable urban environments.

Conduct more detailed studies incorporating quantitative analysis of soil properties (particle size distribution, organic matter content, bulk density) alongside infiltration measurements.Investigate the long-term effects of various vegetation types (e.g., turfgrass vs. native xeric landscaping) and soil amendment practices (e.g., compost application, biochar) on infiltration rates in the soils of Tucson’s urban parks. Monitor infiltration rates seasonally to understand temporal dynamics.Expand the study to a broader range of urban green spaces and land use to develop a comprehensive hydrological map for the city.Evaluate the cost-effectiveness of different soil improvement techniques in enhancing infiltration and reducing stormwater management costs.