The contributions of individual factors to the oasis cold island effect intensity in the Heihe River Basin

The oasis cold island effect, a common phenomenon whereby surface temperatures in oases are lower than those in surrounding desert areas, profoundly impacts the lives of oasis residents. Although previous studies have verified the importance of the Bowen ratio regarding the oasis cold island effect intensity during summer, the contributions of other factors (e.g., aerodynamic resistance) remain to be investigated in more detail. Here, considering two paired micrometeorological observation sites (i.e., one site in an oasis and an adjacent site in a desert area) and two attribution methods (i.e., the intrinsic biophysical mechanism (IBM) and two-resistance mechanism (TRM)), we quantitatively apportion the daytime oasis cold island effect intensity to atmospheric factors (e.g., incoming shortwave radiation, incoming longwave radiation, air temperature, pressure, and specific humidity) and surface factors (e.g., heat storage, aerodynamic resistance, surface resistance, surface albedo and emissivity). The results indicate that both methods can be applied to model the oasis cold island effect intensity accurately, and these methods are insensitive to a relatively small energy imbalance (e.g., similar to 14% in our study). Furthermore, both methods reveal that in summer, the surface resistance and aerodynamic resistance are the two key factors that control the oasis cold island effect intensity, whereas in winter, the aerodynamic resistance (i.e., convection efficiency) becomes the dominant contributor. This highlights the appreciable role of the aerodynamic resistance in the oasis cold island effect intensity. Moreover, from a long-term sustainability viewpoint, we argue that an increase in convection efficiency (i.e., indigenous higher-drought tolerance vegetation and more shelterbelts) across the oasis is one important way to maintain and enhance the oasis cold island effect intensity in the future.