Urban microclimate has been studied for decades – with great advancements in understanding how the material, size, geometry, orientation, and spatial distribution of buildings affect ventilation and net radiation, and therefore the microclimate, in cities. One of the main concerns has been (and continues to be) the alleviation of thermal discomfort. Cities tend to be hotter than the surrounding areas due to what is called the “heat island” effect, mostly attributed to lower vegetation cover and less surface water, which results in less dissipation of energy through evaporation of water (latent heat) and therefore more heating of surfaces and air. The economic implications are significant: it has been estimated that if the air temperature in a city is 5°C higher than in the surrounding areas, the relative power consumption for cooling may be 15-25% higher. The issue of thermal comfort is becoming all the more pressing as cities are projected to continue to expand and climate change is expected to increase average global temperatures as well as the frequency of extreme heat wave events. One of the primary, and perhaps most intuitive, solutions to reduce the heat island effect is to increase the percentage of evaporative surfaces such as vegetation and free water. In addition to reducing the temperature, vegetation can reduce a city’s net emission of CO₂ and improve air quality. This is even more critical in arid environments that have a warmer baseline, and where cities are becoming unbearably hot. However, no long-term data exists on urban evapotranspiration in arid or semi-arid environments, where understanding of the use of scarce water resources makes the issue arguably even more important.

My first proposition is to quantify evapotranspiration as a first effort to obtain long-term measurements in a semi-arid region, using a state-of-the art measurement system in Beer Sheva. I would rely on my experience in looking at evapotranspiration and plant-water relations in agricultural settings, a type of expertise that I believe, would provide an opportunity to bridge some of the gaps in understanding that currently exist in the urban microclimate community.

My second proposition is to quantify the contribution of different evaporating and transpiring components of green areas to the total evapotranspiration flux. In environments where water is not limited, evaporation is often a small fraction of evapotranspiration, which is why evapotranspiration usually can be used as a proxy for transpiration. However, in arid environments, the fraction of evaporation may be quite substantial. In the urban context, moreover, the diverse nature of green spaces means that there are multiple sources of transpiration. As described above, there are modeling approaches that take this into account, but validation has been very limited.

In summary, my future research would address the need to better physically quantify the contribution of green spaces to the urban microclimate, across daily, weekly and seasonal timescales, in a semi-arid environment. Considering there is a major push within Beer Sheva to develop green and blue spaces, long-term measurements can both help inform planning of future green/blue infrastructure and evaluate the effectiveness of various existing configurations. Better understanding of edge effects and competition between plants can improve modeling of their effect on the urban microclimate, which would allow testing different scenarios, and optimizing green space configurations to maximize use of scarce water resources, as well as the ecosystem services provided by these spaces: thermal comfort (which directly affects energy consumption related to cooling/heating buildings), mitigation of CO₂ emissions, and benefits associated with increased biodiversity.

This, and much more, is what we missed.