## 4 Validation of Water Body Temperature Field Calculation Model and Analysis of Test Results  
### Spatiotemporal Evolution of Vertical Profile Temperature in Water Bodies  
From 08:00 in the morning to 22:00 at night, the vertical profile temperature of the water body was continuously measured using a CTD instrument, resulting in a daily variation color map of the vertical temperature distribution of the water body. Figure 4(a),b present the test results for two typical diurnal measurement periods. Figure 5(a),b show the corresponding diurnal wind speed and solar shortwave radiation curves over time for the measurement dates. On Day 1, the solar radiation intensity was relatively low, with solar shortwave radiation ranging from 0 to 350 W/m\({}^{2}\). During the period from 08:00 to 12:00, the solar radiation intensity remained mostly below 200 W/m\({}^{2}\), while the wind speed stayed at a high level, leading to significant turbulence at the water surface. Consequently, the temperature increase in the upper water layer was relatively slow during this period. From 12:00 to 17:00, the solar radiation intensity gradually increased, and the wind speed decreased, causing the surface water temperature to rise. The heating effect of solar radiation, driven by thermal conduction, gradually diffused downward into deeper  
Figure 4: Test diagram of water temperature field. water layers, but its influence was limited to within a depth of 1 m. From 17:00 to 22:00, the solar radiation intensity significantly decreased, eventually dropping to zero. During this phase, the water body radiated heat outward, and the surface water temperature gradually decreased. Notably, between 19:00 and 22:00, an isothermal layer formed within the upper 0 to 0.5 m of the water body. During this period, as solar radiation ceased, the water body began to radiate heat outward. The heat exchange between the water body and the atmospheric environment was relatively weak, while a strong temperature gradient existed within the water body. Turbulence between different water layers became dominant, and under the influence of external disturbances and heat conduction, the temperature of the upper water layer redistributed, becoming more uniform. Comparing Figure 6a,b, it is evident that the solar radiation intensity on Day 2 was significantly higher than on Day 1, with a peak exceeding 800 W/m\({}^{2}\). The range and intensity of the water temperature affected by solar radiation were also notably higher on Day 2. The maximum surface temperature variation on Day 2 reached 3.9 K, and the maximum depth of solar radiation influence extended to 2.3 m. This demonstrates that solar radiation plays a decisive role in the vertical temperature distribution of the water body. Additionally, as shown in Figure 5b, after solar radiation dropped to zero on Day 2, an isothermal layer similar to that on Day 1 formed at the water surface, and the thickness of this layer gradually increased over time. Figure 7a,b present the diurnal variation simulation results of the vertical temperature profile for Day 1 and Day 2, respectively. Overall, the spatiotemporal evolution of the temperature profile predicted by the computational model aligns well with the measured results. Combined with Figure 8, it can be observed that the discrepancy between the simulated and measured results remains mostly within \(\pm\)0.2 K across most depths and times. Temporally, the errors are primarily concentrated during periods of high solar radiation intensity, while spatially, they are mainly found in the upper water layers. For Day 1, dur  
Figure 5: Color map of temperature evolution in vertical profile of water body. Figure 6: Diurnal wind speed and solar shortwave radiation curve with time. ing periods of high solar radiation, the simulation results show lower temperatures in the upper water layers and higher temperatures in the lower layers compared to the measured data, while the bottom water temperature remains relatively stable.