Explanation: The question addresses the excess rainfall experienced during the Kerala floods, specifically focusing on the percentage increase in rainfall compared to the usual rainfall patterns in the state. To understand this concept, it is essential to know how to calculate percentage increase and to have accurate data on the rainfall during the flood period and the average rainfall for the same period in previous years.
The percentage increase in rainfall is calculated using the formula:
\[ \text{Percentage Increase} = \left( \frac{\text{Excess Rainfall}}{\text{Usual Rainfall}} \right) \times 100 \]
In the context of the Kerala floods, the excess rainfall was significantly higher than the usual rainfall. The data indicates that the rainfall during the flood period was approximately 75% more than the average rainfall for the same period in previous years. This means that if the usual rainfall for a particular period is \( R \), the rainfall during the flood period was \( R + 0.75R = 1.75R \).
The correct answer is 75%, which accurately represents the excess rainfall during the Kerala floods. This percentage is derived from the comparison of the actual rainfall during the flood period to the average rainfall for the same period in previous years. The other options (59%, 90%, and 25%) are incorrect because they do not accurately reflect the excess rainfall experienced during the floods.
Understanding the percentage increase in rainfall is crucial for analyzing the severity of the floods and for planning future flood mitigation measures. It also helps in understanding the impact of climate change on rainfall patterns and the potential for future extreme weather events.