• Introduction
  • About the Module
  • Flooding in South Africa
  • About the Case
• Overview of the Rainfall and Flooding Season
  • Rainfall Accumulation Data
  • Provincial Seasonal Rainfall Graphs
  • Provincial Seasonal Rainfall Map
  • Station Rainfall Maps
• Combining Hydrological and Rainfall Data
  • Combined 7-Day Rainfall Accumulation vs. Dam Percent Capacity
• Satellite and NWP Data
  • Overview
  • WV Imagery Overlaid with Model Wind Fields
  • Upper-Level Low over Namibia
  • Moisture Advection
  • Comparing Cyclonic and Anti-Cyclonic Systems
  • Direction of the System
• RADAR Rainfall Estimates
  • SAWS Radar
  • Radar Data for 21 January 2010
• Hydro-Estimator
  • Overview
  • HE Data for 21 January 2010
• Integrating the Data
  • Making the Forecast
  • Taking Action
  • Combined 15-Day Rainfall Accumulation vs. Dam Percent Capacity
  • Real-Time Vs. Predicted Percent Capacity of the Dam
  • Conclusion
• Soil Moisture Products
  • ASAR GM
  • ASCAT
  • SMOS
• Flash Flood Guidance
  • SAWS Flash Flood Guidance System
• Conclusion
  • From 1996 to 2010
  • Recommendations

Radar Data for 21 January 2010

Here's the 24-hour rainfall accumulation data from the SAWS radar network for the Johannesburg area on 21 January 2010 at 12Z. What does it indicate about rainfall in the area over the past 24 hours?

a) It received no rain

b) It received 0 to 10 mm of rain

c) It received 10 to 30 mm of rain

d) It received 30 to 80 mm of rain

The correct answer is C.

The radar rainfall accumulation indicates that 10 to 25 mm of rain on average fell over the Johannesburg area during the previous 24 hours, with 40 mm calculated locally. Note that the daily rainfall totals show different amounts: 10 mm were actually measured. This discrepancy is not unusual. Radar and rain gauges are different technologies and have distinct advantages and disadvantages.