Introduction:
Areal characteristics of a rainstorm refer to the spatial distribution of rainfall over a given area. These characteristics are important for various hydrological and hydraulic applications, such as flood forecasting, water resources management, and urban drainage design. There are different methods and tools used to represent the areal characteristics of a rainstorm, and one of them is the DAD curve.

DAD Curve:
The DAD curve stands for "Depth-Area-Duration" curve and is commonly used to represent the areal characteristics of a rainstorm. It plots the rainfall depth (in millimeters or inches) against the area (in square kilometers or square miles) for a specific duration of the storm event. The DAD curve helps in understanding the spatial distribution of rainfall over a given area and provides valuable information for hydrological analysis.

Interpreting the DAD Curve:
The DAD curve provides insights into how rainfall depth varies with the area affected by the storm. The curve can have different shapes, indicating different spatial patterns of rainfall. Some key points to consider when interpreting the DAD curve are:

1. Steepness of the Curve: A steeper curve indicates a more localized storm, where rainfall intensity decreases rapidly with distance from the storm center. On the other hand, a flatter curve suggests a more widespread storm, with rainfall being more evenly distributed over a larger area.

2. Peak Rainfall Depth: The highest point on the DAD curve represents the maximum rainfall depth for the given duration. This point indicates the area that experienced the most intense rainfall during the storm event.

3. Duration: The DAD curve can be plotted for different storm durations, such as 1-hour, 6-hour, or 24-hour storms. By comparing the DAD curves for different durations, one can understand how the spatial distribution of rainfall changes with time.

4. Design Considerations: The DAD curve is also used in hydraulic and hydrological design, such as designing stormwater drainage systems or estimating flood volumes. The curve helps in determining the appropriate rainfall intensity and duration to be used for design purposes.

Conclusion:
In conclusion, the DAD curve is a graphical representation of the areal characteristics of a rainstorm. It provides valuable information about the spatial distribution of rainfall over a given area and helps in understanding the intensity, duration, and extent of the storm event. By analyzing the DAD curve, engineers and hydrologists can make informed decisions regarding flood forecasting, water resources management, and urban drainage design.