• 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

About the Module

Short-term weather forecasting classically works in the one- to seven-day time frame. However, large-scale and widespread flooding does not result from a single weather event that can be covered by a short-term forecast. Rather, it comes from persistent rainfall over a catchment region during an entire rainfall season, which saturates the ground and leaves areas susceptible to flooding. This means that forecasters should have a comprehensive understanding of the atmospheric and ground surface environment at all times and be able to incorporate information about current surface conditions in their short-term weather forecasts.

This module examines a variety of meteorological and hydrological products that can improve the quality of heavy rainfall forecasts and assist with hydrological management during extensive precipitation events. Some of these are meteorology products that forecasters typically use, such as satellite imagery, numerical weather prediction products, and radar data (when available). But there are a host of new satellite-based hydrological products that are available to forecasters and provide critical information about ground surface conditions. We will introduce several soil moisture products (ASCAT, SMOS, and ASAR GM), and the hydro-estimator, which provides precipitation estimates. The products will be presented within the context of a case, the flooding of South Africa's Vaal Dam in 2009/2010. (Note to learners outside South Africa: The term "dam" refers to man-made accumulations of water behind a barrier. This is called a "reservoir" in some places. The barrier itself is called the" dam wall.")

The module is intended for operational forecasters. Meteorology students and weather enthusiasts should also find the material useful.

By the end of the module, learners should be able to do the following:

• Explain why it is important for weather forecasters to have a holistic understanding of meteorological and hydrological conditions at all times

• Describe the benefits of combining data from different meteorological and hydrological sources when dealing with heavy rainfall situations that can potentially lead to flooding

• Describe the hydro-estimator and the ASCAT, SMOS, ASAR GM soil moisture products and the benefits of using them in the forecast process

• Describe the importance of communicating with hydrological management when heavy rainfall and flooding are a concern

To get the most out of this module, learners should have a basic understanding of meteorology, forecasting, and hydrology. For information about hydrology, see The COMET® Program’s online international hydrology course at https://www.meted.ucar.edu/training_course.php?id=24. Note that COMET modules are free and available to all users but require registration.