Assessment of the potential for rainwater resource utilization in typical cities in northern China

In recent years, arid and semi-arid cities in northern China, such as Ordos City (located at 37°35’24″N–40°51′20″N, 106°42′40″E–111°27′20″E in the Inner Mongolia Autonomous Region), have faced severe water scarcity and vegetation degradation due to the combined pressures of climate change and intensive human activities. This situation necessitates scientifically quantifying the potential for utilizing rainwater resources to alleviate urban water stress. This research uses Ordos as a case study, employing daily precipitation data from 11 national meteorological stations for the period 1958–2022, sourced from the National Tibetan Plateau Data Center. The study investigates the spatiotemporal evolution of precipitation and evaluates the rainwater harvesting potential in its 361 km² main urban area. The findings aim to provide a scientific reference for improving rainwater resource utilization in arid cities.

The methodological framework integrates several analytical tools: linear regression analysis is applied to detect precipitation trends, revealing a non-significant decline of 3.30 mm per decade in annual precipitation, with spring (－0.20 mm/decade) and summer (－3.60 mm/decade) showing decreasing trends, while autumn (+0.60 mm/decade) and winter (+0.30 mm/decade) exhibit marginal increases. The Mann-Kendall test identifies a major abrupt change point in 1961, indicating a shift from wet to dry phases in the precipitation regime. Spatial interpolation demonstrates a consistent precipitation gradient from southeast to northwest, with the main urban area and eastern regions receiving significantly more rainfall than western areas, highlighting their strategic suitability for rainwater collection. A modified SCS-CN (Soil Conservation Service-Curve Number) model is developed, incorporating three land use types and USDA soil classes (B: sandy loam, C: loam, D: clay), with an initial abstraction factor (λ=0.2) under Antecedent Moisture Condition II (AMC II). The model simulates runoff depths across five hydrological scenarios: 10% (wet year, 375.74 mm), 25% (moderately wet, 337.41 mm), 50% (median, 306.49 mm), 75% (moderately dry, 267.92 mm), and 90% (dry year, 237.80 mm). The theoretical potential for rainwater utilization ranges from 45.342 6 million m³ in dry years to 87.611 million m³ in wet years, with a mean annual volume of 73.501 8 million m³. This estimate is validated using a runoff coefficient method, applying a coefficient of 0.67 as per GB 50015–2019, which yields a mean value of 66.331 9 million m³, thereby confirming the model’s reliability. Although the urban construction land area is relatively small, its extensive impermeable surfaces result in runoff comprising a significant portion of the total, highlighting the critical role of this zone in rainwater generation.

Key implementation constraints include the seasonal concentration of 85% of rainfall between June and October, high evaporation losses, and inadequate infrastructure. To address these, strategic recommendations are proposed: First, in light of Ordos’s actual conditions, it is necessary to establish rainwater collection and utilization infrastructure. In urban planning, the design and construction of such facilities—such as underground storage tanks and water cellars—should be prioritized to effectively capture and use rainwater. Second, optimize water resource allocation. Considering urban water demand and the potential of rainwater resources, improve the water allocation strategy by incorporating rainwater into the urban water management system. Third, enhance public education and awareness regarding rainwater resource utilization. Through media campaigns, community redevelopment, and related initiatives, public recognition can be further enhanced, fostering widespread societal participation.