To calculate the percentage increase between the two years, we need to first calculate the difference in the amount of rainfall between the two years:
Difference = 15 inches - 12 inches = 3 inches
Next, we need to calculate the percent increase, which is the difference as a percentage of the original value (the rainfall in 2020):
Percent Increase = (Difference / 12 inches) x 100%
Plugging in the values, we get:
Percent Increase = (3 inches / 12 inches) x 100%
Percent Increase = 0.25 x 100%
Percent Increase = 25%
Therefore, the percentage increase in rainfall between 2020 and 2021 is 25%.