Cumulative Rainfall in mm per Hour

Accumulated rainfall: summing precipitation over time

Accumulated rainfall is the total depth of water that lands on a surface over a set period, measured in millimetres. The handy rule of thumb is that 1 mm of rain = 1 litre per square metre, so a daily, monthly or annual total is nothing more than the sum of the hourly mm/h readings across that window. Take a station that logs 1.2, 3.4, 5.0, 2.1 and 0.8 mm/h over five hours: that adds up to 12.5 mm, or 12.5 L/m². São Paulo averages around 1,500 mm/year, Amazonas routinely tops 2,500 mm, and the Northeast sertão stays below 800 mm. When the accumulated total crosses the thresholds tied to landslide and flood risk, CEMADEN puts out civil-defence alerts.

Applications

Planning crops and irrigation, tracking surface and groundwater hydrology, running reservoirs and dams, issuing flood and landslide alerts (CEMADEN, Defesa Civil), sizing urban drainage, monitoring climate and building drought indices, estimating insurance losses and putting together agro-meteorological forecasts.

FAQ

Is 1 mm of rain really 1 litre per square metre? It is. A 1 mm layer spread evenly across 1 m² comes out to exactly 1 litre of water, no matter what the surface is.

How is accumulated rainfall measured? With pluviometers, either manual or tipping-bucket, and with weather radar, adding up the instantaneous rates over whatever period you care about.

What is the difference between accumulated and intensity? Accumulation is how much fell in total over a period (mm), while intensity is how fast it came down (mm/h).