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Water scarcity is a growing global concern, resulting from drastic climate and societal changes witnessed over the past few decades. Previous attention has predominantly focused on inadequate water quantity as the main cause of water scarcity, but pollution-induced water scarcity has been largely overlooked. Furthermore, there is a lack of understanding about the effectiveness of policy interventions in mitigating water scarcity and its social impact. To address these knowledge gaps, we developed an ecosystem service-based approach to measure quantity- and quality-related water scarcity by comparing supply of and demand for water provision and water purification services. We also developed several water and land management scenarios to examine their potential in alleviating water scarcity under different climate conditions and water quality requirements. Our case study in the Taihu Basin of southeastern China identified four types of water scarcity status across different sub-basins, including quantity-based, quality-based, quantity- and quality-based, and no water scarcity. The degradation of water quality in the Taihu Basin has exacerbated the scarcity of clean water supply. Water conservation measures effectively alleviated quantity-based water scarcity, while nitrogen reduction and grain for green (i.e., conversion of cropland into forest land) exhibited similar efficacy in alleviating quality-based water scarcity. Integrating these measures contributed to alleviating both quantity- and quality-based water scarcity. However, the effectiveness of these measures decreased under drier climate conditions and higher water quality requirements, highlighting the importance of climate and water quality in determining the magnitude, extent, and severity of water scarcity. The approaches and findings presented here provide new insights into the sustainable management of water resources in the Taihu Basin and other similar basins worldwide. • Quantity- and quality-related water scarcity were assessed using an ecosystem service-based approach. • Water scarcity was influenced by changes in climate, land use, and water quality requirement. • Water pollution exacerbated water scarcity in the Taihu Basin of China. • The impact of water scarcity on human populations was further enlarged due to spatial mismatches. • Improved water and land management strategies could potentially alleviate water scarcity. [ABSTRACT FROM AUTHOR]

Although it is challenging to integrate supply and demand to comprehensively understand urbanization effects on ecosystem services, this knowledge is essential, especially in rapidly urbanizing areas. A spatially explicit approach was developed here to synthesize supply and demand dynamics of the two most important hydrologic services in the rapidly urbanizing Taihu Lake Basin (TLB) of eastern China. The supply of water purification (WP S) and flood mitigation (FM S) were measured as nitrogen removal and runoff retention, respectively. Whereas the demand for water purification (WP D) was quantified as the difference between total and permitted nitrogen loading based on relevant water quality standards, the demand for flood mitigation (FM D) was estimated as the vulnerability to potential flood damage, including economic losses and causalities. We found a spatial mismatch where high WP S and FM S occurred in mountainous areas while high WP D and FM D concentrated in urban and agricultural areas across the basin. WP S and WP D decreased by 10% and 20%, respectively during 2000–2015, due mainly to loss of croplands to urban expansion. This was also the main cause of decreased FM S by 7% but increased FM D by 67%, which underscored the importance of conserving croplands in rapidly urbanizing regions of the TLB. Overall, land use composition had strong associations with WP D (r 2 ≥ 0.57) and FM S (r 2 ≥ 0.38) at the sub-basin scale, while the configuration of multiple land uses, such as urban sprawl, cropland fragmentation, and riparian buffers were crucial in influencing WP S. In comparison, FM D was most sensitive to urban expansion (r 2 = 0.74), economic development (r 2 = 0.81), and population growth (r 2 = 0.93). These findings provide new insights into sustainable land management for coordinating supply of and demand for hydrologic services in the TLB and other urbanizing watersheds of the world. • Supply and demand dynamics of hydrologic services are quantified in an urbanizing watershed. • Spatial mismatches between supply of and demand for hydrologic services are revealed. • Urbanization and land use have strong effects on hydrologic services at the sub-basin scale. • Land management measures are proposed to coordinate hydrologic service supply and demand. [ABSTRACT FROM AUTHOR]