为了解密云灾情，先学些地理知识

Group 1 - The article discusses the impact of extreme weather events, specifically heavy rainfall and flooding, in the Miyun district of Beijing, highlighting the differences in disaster severity across various regions within Miyun [3][11]. - The rainfall exceeded 300 millimeters in a short period, leading to significant geological disasters, including road damage, power outages, and landslides, particularly affecting residents in mountainous areas [7][11]. - The flooding in Taishitun was exacerbated by upstream rainfall from areas like Chengde, resulting in unexpected disaster despite being outside the red alert zone [8][9]. Group 2 - The article explains the hydrological dynamics of the Baihe and Chaohe rivers, which both flow into the Miyun Reservoir, and how their water levels were affected by recent heavy rains from both local and upstream sources [13][21]. - The Miyun Reservoir experienced its highest inflow since its establishment in 1959, with peak inflow rates reaching 6,550 cubic meters per second, indicating a significant hydrological event [21][40]. - The article describes the changes in water quality and flow characteristics during the reservoir's controlled release, noting that the river's appearance changed dramatically due to sediment and debris being washed into the water [36][38].