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Nowadays, climate change and heat extremes are becoming highly challenging problems in many cities across the globe. One of the solutions to overcome this problem is the use of vegetation, and, in particular, extending the range of overgrown areas, which are sometimes referred to as “urban green areas.” In this paper, the moisture condition and its mitigating effect on Land Surface Temperature in urban areas were examined in Warsaw, Poland, using satellite data. To do so, the so-called “Triangle Method” was employed. The triangle method is based on a Land Surface Temperature–Normalized Difference Vegetation Index (LST-NDVI) scatterplot to calculate the Temperature Vegetation Dryness Index (TVDI) and its modification–quadratic Temperature Vegetation Dryness Index (qTVDI). This article discusses, in detail, the usefulness of the triangle method for the analyses of built-up areas. The drought satellite indices TVDI and qTVDI compared with those of LST, NDVI, and NDBI (Normalized Difference Building Index). The study shows that the triangle method based on LST-NDVI scatterplot analysis is a promising tool for establishing moisture conditions over urban areas and for studying the effect of vegetation impact on urban heat islands. Detailed analysis shows that over an urban area, qTVDI shows better agreement with LST than classic TVDI. Full article

The temperature of a city’s surface is influenced by many factors, including human-dependent ones that can be shaped, such as the urban density, the condition of urban vegetation, the presence of urban water bodies, and soil moisture. Knowledge on this subject allows for improving the urban climate through better planning and construction of urban infrastructure and adapting cities to climate change and avoiding deadly heat waves increasingly threatening European cities. So far, mainly the first three factors have been studied particularly well, while there is no in-depth research on the impact of soil moisture on a city’s climate in the literature. This article fills this gap by analyzing the impact of all the abovementioned factors on the temperature of the city’s surface in Warsaw, a large European urban agglomeration, located in a temperate climate zone. Due to the exceptionally large war damage to Warsaw during World War II, rapid postwar reconstruction, and significant expansion, the city is characterized by a very large diversity of urban development density and a much larger amount of green areas compared to most large cities, such as old Western European agglomerations. The scientific novelty of the work is also the fact that the soil moisture content was analyzed using the TVDI/qTVDI (Temperature Vegetation Dryness Index Estimation) indexes obtained by using the so-called triangle methods in NDVI-LST space, based on satellite observations. Such analyses have not been performed so far in urban areas, while in the article, many new results were obtained on this subject. For example, Pearson’s correlation coefficients between LST, NDBI, NDVI, and qTVDI calculated for the entire area of Warsaw on 8 August 2020 were 0.78, 0.45, and −0.35, respectively. Another important aspect of the work is that it includes comparative studies of the impact of the abovementioned factors on the temperature of the Earth’s surface at the level of different city districts. As a result, it was possible to more effectively study the impact of the abovementioned factors on the temperature of the Earth’s surface at the scale of local administrative units. Thanks to the obtained results, urban planners will be able to reduce urban hazard risks caused by climate change. Full article