Forecasting hazards, averting disasters

2.1.4   Forecast lead time

Forecast lead times in the systems surveyed vary from 

days through to seasons (and up to 12 months in 

advance of acute humanitarian impacts of drought). The 

lead time depends in part on the hazard system under 

study, with short lead times (typically days) for pluvial 

flooding from heavy rain and heat/cold waves, days 

to weeks for fluvial flooding, depending on river basin 

size, and months for drought and food security hazards. 

Systems using forecasts can generally provide longer 

lead times than those based on monitoring information, 

although monitoring can provide usefully long lead times 

in more slowly evolving systems, for example in larger 

river basins (the Mono river in Togo is one example), and 

for drought/food security. 

A small number of systems operate over a range of 

forecast lead times, drawing on forecast information 

from seasons through to days. This can allow for the 

progressive staging of actions. A notable example is the 

Red Cross extreme rain/flood hazard system in Peru (see 

Figure 2), which involves preparedness actions triggered 

automatically by forecasts at various lead times (days/

month/season).