在R的ggplot2中按温度异常用红蓝渐变填充两条线间区域

需求说明 #

基于当年月均温与历史月均温数据，在ggplot2中填充两条曲线间的区域：

• 当年气温高于历史时（正异常）填充红色，异常值越高颜色越深
• 当年气温低于历史时（负异常）填充蓝色，异常值越低颜色越深

数据准备 #

df <- data.frame(
  month = c("01", "02", "03", "04", "05", "06", "07", "08", "09", "10", "11", "12"),
  tmean = c(20, 22, 20, 28, 30, 32, 34, 33, 30, 27, 24, 18),
  tmean_ref = c(18, 20, 23, 27, 29, 31, 33, 32, 29, 26, 22, 19),
  tano = c(2, 2, -3, 1, 1, 1, 1, 1, 1, 1, 2, -1),
  tano_label = c("+2", "+2", "-3", "+1", "+1", "+1", "+1", "+1", "+1", "+1", "+2", "-1")
)
# 将月份转为有序因子，确保x轴按自然顺序排列
df$month <- factor(df$month, levels = c("01", "02", "03", "04", "05", "06", "07", "08", "09", "10", "11", "12"))

完整代码实现 #

library(ggplot2)
library(ggrepel)

ggplot(data = df, aes(x = month, group = 1)) +
  # 填充两条曲线间的区域，映射填充色为异常值tano
  geom_ribbon(aes(ymin = pmin(tmean, tmean_ref), 
                  ymax = pmax(tmean, tmean_ref), 
                  fill = tano),
              alpha = 0.6) +
  # 设置渐变配色：负异常蓝色，正异常红色，中间白色
  scale_fill_gradient2(low = "#1a75ff", mid = "white", high = "#ff4d4d",
                       midpoint = 0, name = "气温异常值(℃)") +
  # 当年气温实线
  geom_line(aes(y = tmean), linewidth = 0.85, lineend = "round", na.rm = TRUE) +
  # 历史气温虚线
  geom_line(aes(y = tmean_ref), linetype = "longdash", na.rm = TRUE) +
  # 当年气温数据点
  geom_point(aes(y = tmean), na.rm = TRUE) +
  # 异常值标签
  geom_label_repel(aes(y = tmean, label = tano_label), segment.color = NA, na.rm = TRUE) +
  # 调整主题与标签
  labs(x = "月份", y = "平均气温(℃)", title = "当年与历史月均温对比及气温异常") +
  theme_minimal()

代码关键说明 #

• geom_ribbon：通过ymin和ymax分别取两条气温线的最小值和最大值，实现区域填充；将fill映射到tano（气温异常值），为渐变效果提供依据
• scale_fill_gradient2：自定义三色渐变配色，以0为中点区分正负异常，同时设置颜色名称用于图例
• 调整月份为有序因子：避免x轴月份按字符排序出现混乱

内容的提问来源于stack exchange，提问作者piblo95