Estimating the Benefit of TRMM Tropical Cyclone Data in Saving Lives

A technique is developed and presented to estimate the quantitative benefit of satellite data on tropical cyclone forecasting in terms of additional lives saved. The technique is applied to the case of the Tropical Rainfall Measuring Mission (TRMM), a research mission developed by NASA and the Japanese space agency, JAXA. In addition to its data being used for research on rainfall climatology and precipitation processes, TRMM data are also used operationally by weather agencies in the U.S. and elsewhere for tropical cyclone monitoring and forecasting.

The technique ties together information on the magnitude of the decrease in hurricane mortality in the U.S. (89%) and information on the decrease of 24-hour forecast errors of storm position (28%), both over the past 50 years. The cause and effect relationship between these two variables is discussed and taken into account by assuming only a fraction (f) of the mortality decrease is due to forecast improvement. The impact of TRMM data in improving the 24-hour forecast is estimated based on improved initial storm position error information and on results from numerical forecast models. The relationship is extrapolated from the U.S. to the globe using an estimated number of deaths worldwide due to tropical cyclones. Approximately 90,000 people perished worldwide due to “floods” and 60,000 died due to “windstorms” during the decade between 1993-2002 according to the World Disasters Report. For the purposes of this exercise it is assumed that about 10,000 people die per year due to tropical cyclones, certainly the main cause of both floods and windstorms over much of the globe. Incorporating this information into the derived formula, assuming f = 0.5 and that TRMM has only a conservative, 1% (scalable) impact on the forecast, results in an estimate of 160 lives/year saved due to the operational use of TRMM data. Over the seven years of the satellite (so far) this would convert to a total of over a 1000 lives saved by TRMM. The sensitivity of the calculation is examined and the result is compared to the estimated risk of injury to people on the Earth's surface (1/5000) due to orbital debris during a possible uncontrolled re-entry into the atmosphere of the TRMM satellite. The role of such calculations and comparisons in decisions related to satellite operations and methods of disposal is also discussed.