## 5 Results
### Dynamic Analysis of Night-time Light Changes at the Regional Scale  
Using the ratio of the total amount of night-time light during the conflict and the total level of night-time light before the conflict, in turn, the daily night-time light ratio index of the Ukrainian regions is attained, with the date as the horizontal axis and the night-time light ratio index as the vertical axis on the presented line graphs; the vertical axis scale is adapted to each region. The night-time light ratio index is shown in Figure 5. When NLRI = 1, it means a return to the pre-war night-time light level. Figure 4: Ukraine’s night-time light ratio index from 23 February to 1 April. Overall, almost all of the region's night-time light ratio indexes show a decreasing trend in the early stages of the war, then an increase in the middle period, and then decrease again in the later period. This research divides the period into three segments. The first lasted from 28 February to 18 March, and the average night-time light ratio index of each region is shown in Table 2. After the outbreak of the Russian-Ukrainian conflict, most regions lost more than 50% of their night-time light. Within five days of the outbreak of the conflict, from 24 February to 28 February, the states that responded quickly to the war showed a short \"L-shaped\" or sinking segment in the line chart, and most of these were in Eastern and Northern Ukraine, where Luhans'k Oblast lost 90% of its night-time light, Kharkiv lost 87% of its night-time light, Chernihiv Oblast lost 88% of its night-time light, and Zaporizhizhya Oblast lost 87% of its night-time light. At this time, these regions were in the conflict zone between Russia and Ukraine. The fighting during this period was very fierce, and the night-time lights reduced rapidly in these areas. On the other hand, the night-time light response speed of the regions located in central Ukraine was relatively slow overall, but due to the rapid advance of the Russian army, the night-time light loss rate of the central cities was still very fast. A transition period of night-time light loss in these areas can be seen, which is shown in the line chart to have a long \"L-shaped\" opening section. Of these regions, Kiev Oblast lost 74% of its night-time light, Kirovchrad Oblast lost 64% of its night-time light, and Vinnytsya Oblast lost 60% of its night-time light, as they were affected by the different geographical locations of the major cities in each region in regard to the outbreak of the conflict. The change in night-time lights is also varied, and the closer a region is to the combat zone, the more dramatic the reaction. Most of the regions with the \"N-shaped\" beginning are located on the western side of Ukraine. These regions, such as Volyn and L'viv, are relatively far away from the combat zone and have seen no large-scale advance of the Russian army. Figure 5: _Cont._  
From 1 March to 18 March, almost all the regions showed an upward trend in terms of the total amount of night-time light. The slowing of the battlefield situation, the repeated joint talks between Russia and Ukraine, and the active silence of the Russian side have somewhat stabilized civilian life and thus brought about the restoration of night-time lights. The states with pro-Russian power concentrations are highlighted by the rapid restoration of night-time light to pre-war night-time light levels. For instance, the Donets'k region returned to 87% of its pre-war night-time light levels on 5 March and the Luhans'k region achieved the same on 6 March, when it returned to 89% of its night-time light before the war. These states have seen fewer overt military-civilian conflicts, and civilians have made fewer attempts at fleeing. The loss of night-time lights was therefore quickly remedied. In regard to the Russian-controlled areas, except for Donets'k and Luhans'k, the Crimean Autonomous Region, Sevastopol' Port, and the Kherson Region have all returned to pre-war levels of light.