Droughts are serious natural hazards, especially in semi-arid regions. They are also difficult to characterize. Various summary metrics representing the dryness level, denoted drought indices, have been developed to quantify droughts. They typically lump meteorological variables and can thus directly be computed from the outputs of regional climate models in climate-change assessments. While it is generally accepted that drought risks in semi-arid climates will increase in the future, quantifying this increase using climate model outputs is a complex process that depends on the choice and the accuracy of the drought indices, among other factors. In this study, we compare seven meteorological drought indices that are commonly used to predict future droughts. Our goal is to assess the reliability of these indices to predict hydrological impacts of droughts under changing climatic conditions at the annual timescale. We simulate the hydrological responses of a small catchment in northern Spain to droughts in present and future climate, using an integrated hydrological model calibrated for different irrigation scenarios. We compute the correlation of meteorological drought indices with the simulated hydrological time series (discharge, groundwater levels, and water deficit) and compare changes in the relationships between hydrological variables and drought indices. While correlation coefficients linked with a specific drought index are similar for all tested land uses and climates, the relationship between drought indices and hydrological variables often differs between present and future climate. Drought indices based solely on precipitation often underestimate the hydrological impacts of future droughts, while drought indices that additionally include potential evapotranspiration sometimes overestimate the drought effects. In this study, the drought indices with the smallest bias were the rainfall anomaly index, the reconnaissance drought index, and the standardized precipitation evapotranspiration index. However, the efficiency of these drought indices depends on the hydrological variable of interest and the irrigation scenario. We conclude that meteorological drought indices are able to identify years with restricted water availability in present and future climate. However, these indices are not capable of estimating the severity of hydrological impacts of droughts in future climate. A well-calibrated hydrological model is necessary in this respect.

To successfully reduce their climate impacts, cities need a clear strategical path to decrease their energy consumption and increase their use of renewable energy. Consequently, local energy plans have recently become popular, notably in western Switzerland. These plans propose different pathways towards the achievement of economic, social, and environmental energy objectives, often supported by an action plan describing the possible projects and policies necessary to enact these pathways. However, the implementations of these local energy plans show a strong variability in efficiency and effectiveness. In this study, we survey the state of the implementation of local energy plans in 57 municipalities in western Switzerland. Based on this survey, we make four concrete propositions to reduce the difficulties faced by cities during the implementation of local energy plans and we test these propositions in three partner cities. These new tools, which aim at reinforcing municipal energy policy, can now be reused by local administrations in the study area and beyond.

A key advantage of district heating networks is their ability to integrate different renewable energy sources, from geothermal to solar. However, the success of this integration depends on a variety of design and technical decisions, such as feed-in locations or operating temperatures, which need to be compared and analysed. For this purpose, dynamic models of district heating grids, which allow for an hourly representation of the thermodynamic conditions, are necessary. This type of models are nevertheless still uncommon, drastically limiting options to perform these comparisons accurately. To address this challenge, an open-source tool to model district heating networks is presented here and successfully applied to two case studies in western Switzerland. These simulations are then used in conjunction with simplified models of storage and solar thermal collectors to investigate, in a preliminary way, the impact of solar thermal integration on the mass flow and temperature of the network pipes, illustrating the interest of the proposed method to compare different configurations of renewable heat injections in district heating networks.

We compare simulated energy retrofitting of individual buildings with energy refurbishments optimized at the scale of the neighborhood. For the neighborhood case, buildings can also be connected together through a heat network. We use a detailed three-dimensional model to estimate heating needs (CitySim) and a mixed-integer linear optimizer to analyze different options for energy refurbishment, including various heating technologies. According to our simulations, planning at the neighborhood scale results in slightly lower costs (about -5%) and lower C0₂ emissions (about -60%) than planning energy refurbishment at the building scale, showing that integrated planning of energy refurbishment is beneficial from both environmental and economical points of view.