See below a graph of the Dead Sea level in the past decades?

import stuff 
import numpy as np
import matplotlib.pyplot as plt
import pandas as pd
import seaborn as sns
sns.set(style="ticks", font_scale=1.5)  # white graphs, with large and legible letters
# %matplotlib widget
load file to dataframe 
filename = "../archive/data/dead_sea_level.csv"
df = pd.read_csv(filename)
df['date'] = pd.to_datetime(df['date'], dayfirst=True)
df = df.set_index('date').sort_values(by='date')
# df
plot 
fig, ax = plt.subplots(2, 1, figsize=(8,8), sharex=True)
ax[0].plot(df['level'], color="tab:blue")
ax[0].set(title="Dead Sea Level",
       ylabel="level (m)")
ax[1].plot(df['level'].diff())
ax[1].plot(df['level']*0, ls=":", color="gray")
ax[1].set(ylabel="diff of sea level")
plt.gcf().autofmt_xdate()  # makes slanted dates

We suspect that the operation diff has something to do with derivatives, or rates of change.