Noise Reduction by NBS in Valladolid city

Noise pollution by traffic, construction works, etc. is a common city problem. Nuisance from noise is detrimental to neighbourhood liveability, living comfort and work environments, and can increase risk of serious health problems such as hearing loss and cardiovascular disease.

Urban ecosystems provide noise reduction services by serving as a natural sound buffer. Vegetation provides both a direct and an indirect barrier to environmental noise. Starting with its direct functions, green belts attenuate noise by absorption, dispersal, and destructive interference of sound waves, though sound levels can intensify locally if measured right below tree crowns. Indirect noise reduction effects are generated by lessened wind speeds and the absorptive capacity of pervious soils. UGS also proved to offer noise reducing services via psychological effects: just observing the presence of a green wall can lead people to perceive less noise nuisance or alter the perception of noise as sounds such as flowing water, bird singing, and leaves rustling in the wind mask disturbing background noise.

On the other hand, the methodology proposed for this KPI is based and uses the methodology and tools proposed by the European Commission Working Group Assessment of Exposure to Noise (WG-AEN).

The Environmental Noise Directive (END) requires two main indicators to be applied in the assessment and management of environmental noise. The first indicator (Lden) is the noise level for the day, evening and night periods and is designed to measure ‘annoyance’. The END defines an Lden threshold of 55 dB. The second indicator (Lnight) is the noise level for night-time periods and is designed to assess sleep disturbance. The END defines an Lnight threshold of 50 dB. Member States must report the numbers of people who are exposed to noise levels above both thresholds for each noise source (e.g. roads, railways, airports, industry).

交通、建筑施工等引发的噪声污染是城市常见问题。噪声扰民现象会损害社区宜居性、居住舒适度与工作环境，还会增加听力损失、心血管疾病等严重健康问题的患病风险。

城市生态系统可作为天然声屏障，提供噪声消减服务。植被对环境噪声兼具直接与间接阻隔作用。从直接功能来看，绿化带通过声波吸收、散射以及相消干涉来衰减噪声，但在树冠正下方测量时，局部声级可能会出现升高情况。间接降噪效果则源于风速降低与透水土壤的吸声能力。城市绿地系统（Urban Green Space，UGS）还可通过心理效应实现降噪：仅观察绿墙景观，即可让人们感知到更少的噪声烦扰，或是将噪声感知为流水、鸟鸣、风吹树叶声等悦耳声响，从而掩盖令人烦躁的背景噪声。

另一方面，本关键绩效指标（Key Performance Indicator，KPI）所采用的方法，基于并沿用了欧盟委员会噪声暴露评估工作组（Working Group Assessment of Exposure to Noise, WG-AEN）提出的方法与工具。

《环境噪声指令》（Environmental Noise Directive，END）要求在环境噪声评估与管理工作中采用两项核心指标。第一项指标（Lden）为昼间、傍晚与夜间时段的噪声级，用于衡量“噪声烦扰度”，该指令将Lden阈值设定为55分贝。第二项指标（Lnight）为夜间时段的噪声级，用于评估睡眠干扰情况，该指令将Lnight阈值设定为50分贝。各成员国需上报各类噪声源（如道路交通、铁路、机场、工业噪声）中，暴露于两项阈值以上噪声水平的人口数量。