Impact of longer Drought Periods on Climate in Greater Vienna

The Imp_DroP project deals with the effects of climate change-related dry periods on ground temperatures and water requirements for irrigation in Vienna. The focus of the study is to examine the effects of cooling on the climate of the following components:

• a) Evaporative cooling by  irrigated agricultural regions
• b) Evaporative cooling in urban Vienna (especially green roofs)
• c) Anthropogenic heat reduction

To quantify the effects of these mitigation measures, part of the project consisted of experimental studies: evaporation and precipitation, runoff, growthrate were recorded for two seasons with 10 lysimeters on four green roofs with different urban climates. The in-situ measurement data served as input for the modeling tasks. In a second step, anthropogenic heat emissions were quantified. For this purpose, data from E-Control was used, the energy consumption was broken down in time and space for selected periods and the anthropogenic heat flow was calculated for various scenarios.

Based on all these results, SURFEXv9/TEB was used to examine the local effects of building envelopes, green roof construction, irrigation, tree shade and vegetation in the canyon, traffic heat reduction and other possible climate mitigation measures on indoor, roof and canyon thermal conditions. Anthropogenic heat can lead to local increases in air temperature of up to 2 °C. Reducing anthropogenic heat by reducing traffic, increasing the contribution of renewable local energy production and improving building insulation can reduce air temperature to this extent. Tree shade can reduce the thermal comfort index UTCI by 4 ° during noon. Full irrigated low vegetation can cool between 1-3 °UTCI throughout the day.

The coupled urban climate model WRF-TEB was used to simulate the current and future climate in the greater Vienna area. Climate scenarios suggest that climate change could lead to a temperature increase of around 3.8 °C by mid-century if no significant action is taken.  Remedial measures related to irrigation of the agricultural areas east of Vienna (Marchfeld) can lead to a reduction in the maximum temperature, especially close to the irrigated area. A maximum reduction of only 0.2 °C can be achieved for the entire city, while in the districts of Vienna closer to Marchfeld the reduction can even be up to 0.4 °C. However, if all possible cooling measures are implemented to the maximum, a maximum cooling of 1.5 °C can be achieved.  However, exhausting all adaptation measures cannot compensate for the warming induced by climate change while seriously challenging the water supply of Greater Vienna.