Paving materials can negatively impact the urban climate, but knowledge of the thermal and climatic behavior of multilayer urban structures is lacking, particularly under heatwave conditions. To this aim, a laboratory-scale experiment was developed to characterize pavement samples under heatwave conditions. Surface albedo and evapotranspiration are confirmed as the dominant parameters for surface heating. The thermal properties of the underlying layers of pavement structures also impact their behavior and contribution to the urban climate. In particular, the combination of high effusivity and diffusivity of the granite sidewalk structure allow it to exhibit "cool" behavior during the day and "hot" behavior at night despite its relatively high albedo. A solar transmission index is proposed, including both the radiative and the thermal properties of a structure's constitutive layers, to rank structures by their ability to transmit absorbed radiation in depth. Future work with the developed experimental platform will aim to evaluate the performance and optimize the watering method of pavement-watering for different kinds of pavement structures. Keywords: urban heat island; urban paving materials; thermal properties; heat waves Vz downwards conductive heat flux at depth z [W/m²] Subscript/superscript α albedo [-] emissivity [-] n layer n ref/up reflected or upwards z depth [m]

Many cities are expected to face a strong increase in the frequency and intensity of heatwaves by the end of the 21 st Century due to climate change. In Paris, the frequency of heatwaves could rise from an average of one day per year to 14-26 days per year, with temperatures reaching up to 50°C. Since 2012, pavementwatering is viewed as a potential tool for emergency cooling by the city while scientific work on the technique has found its application to be best suited to densely built urban areas, compared for example to urban greening whose impact may be hindered by lack of available planting space. This paper proposes an interdisciplinary approach combining urban physics with social sciences to develop such a GIS model for pavement-watering as an emergency response to heatwaves in Paris. It is built on performance criteria derived from previous work are input into a Geographic Information System to identify urban areas where pavement-watering would be most effective. In addition, a heat-related health risk assessment is conducted, using microclimatic, urban and socioeconomic layers, to single out areas where heatwave risk is highest in public spaces, combining high temperatures, pedestrian traffic and local population vulnerability. The microclimatic hazard dataset includes a physical model of park and water body cool islands assuming they are driven by thermal diffusion. The resulting tool has significant flexibility in defining the thresholds of the different indicators. The mapping scheme identified a total of 50 to 200 km of high priority areas for pavement-watering, requiring between 1,400 and 5,800 m 3 /day of non-potable water, equivalent to 0.6 to 2.6 L/day per capita. Limitations due to data quality or resolution are discussed as well as paths for further improvement.

Due to their tendency to absorb heat, urban materials participate in the formation of urban heat islands thus contributing to increased health risks during heat waves. Since 2013, the city of Paris has experimented in situ pavement-watering campaigns as an emergency cooling tool during heatwaves. These studies have highlighted the influence of the materials being watered on the optimal watering strategy to adopt. In this regard, a laboratory experiment was developed to study the thermal behaviour of various urban materials under heatwave conditions with or without watering. Here, results from watering an asphalt road structure with twelve different rates are presented to fine-tune the process for optimal cooling. The sample undergoes a heatwave like 24-hour cycle inside a climate chamber. Two distinct cooling regimes are highlighted versus the watering rate, corresponding to the increase of evaporation with the watering rate until maximum evaporation rate is reached. This aspect was used to maximise the cooling efficiency of the method while minimising the water consumption. Using the surface heat budget, the evaporative cooling flux was also determined. Pavement-watering was found to have a great impact on heat stored in the pavement and released to the atmosphere. Results otherwise compare favourably with field observations.

The thermal behavior of 12 standard and cool pavement structures (asphalt, granite, stabilized sand, cobblestones, reflective paints, pervious concretes, dry grass, etc.) coupled with pavement-watering is studied in the lab under heatwave like conditions. Watering is fine-tuned for each structure to maximize cooling and minimize water consumption using two linear cooling regimes, before deployment in the field. The surface heat budget is closely studied and the partitioning of irradiance and net radiation into conductive, convective, radiative and cooling flux at surface is analyzed for each structure. Energy partitioning, surface temperature increase and optimal watering rates all exhibit good correlation with overall surface absorptivity. The transmitted flux at varying depths is also characterized using a transmission index that includes surface absorptivity and apparent conductivity of the traversed layers. Results of this study intend to improve our understanding of the energy balance of cool pavements compared to traditional ones under given weather conditions, as well as that of processes involved in the optimization of their evaporative cooling versus watering rate. Benefits of each pavement, efficiency of the method, limitations of the protocol and its potential transposition to the field are all discussed in this contribution.

The Lowry approach (1977) sets the framework for evaluating the meteorological effects of the urban heat island (UHI), by describing it as the superposition of "background", "local" and "urban" climates. In this paper, by adapting this framework to the study of UHI countermeasures, we propose a statistical method suited for assessing their effects in the field. The framework demonstrates that direct comparisons between case and control sites cannot isolate the impacts of UHI countermeasure. It also shows that the interstation differences before and after countermeasure implementation cannot be considered as statistically independent. Consequently, statistical procedures suited for handling dependent observations are necessary such as a linear mixed or fixed effects model. As a case study, experimental data from pavement-watering experiments conducted in Paris since 2013 are used, with the goal of assessing its cooling effects for two different watering strategies. With the fixed effects model, long-lasting statistically-significant effects are found. Results indicate beneficial thermal effects for pedestrians with reductions of UTCI-equivalent temperature up to 2°C, and duration of statistically-significant effects directly linked to the watered surface area. The method is limited by the number of measurements that must be gathered both before and after the UHI countermeasure implementation.

Like all current industrial systems, agriculture overwhelmingly relies on energy supply from controllable sources, mainly fossil fuels and grid electricity. Power supply from these sources can be adapted to perfectly match the timing of power requirements of demand systems. The energy transition largely consists in substituting renewable power|which is intermittent by nature|to controllable sources, leading to disconnection between instantaneous power production and demand. Energy storage is a potential solution for balancing production and demand and safeguarding the operating conditions of the demand system. In this paper we quantify the effects of renewable power supply (solar and wind) on the operation of a standard poultry farm. We model the balance of power generation and demand considering the growth conditions of poultry and local weather data including temperatures, wind speed and solar radiation. We assess scenarios of renewable power supply in function of the size of the power plant, the wind-to-solar power generation mix and energy storage, and assess the impact of power supply patterns on the operating intensity (productivity) of the demand system. We show that it is possible to achieve non-negligible shares of renewable power supply with a reduced loss of farm productivity regardless of the energy mix by using small storage capacity. However, a full transition to renewable power supply would require a combination of ( i )-large energy storage compared to the annual demand, ( ii )-oversizing the power production plant, and ( iii ) adapting the energy mix to the timing of the power demand. Storage is all the more critical as production and demand are uncorrelated in time. The ratio of useful to unused energy storage by the end of the year varies with the energy mix and operating intensity (productivity) of the farm. We discuss the implications of different energy configurations on the performance of the demand system.

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