Can the current satellite systems observe a change in the Earth's hydrologic cycle?

There has been much speculation of late concerning the effect of warmer atmospheric temperatures on the hydrologic cycle. Most of the concern centers around an increase in tropical storms, flooding, and severe weather which may be associated with an ‘acceleration’ of the hydrologic cycle. The latest IPCC (1996) report, which examines possible changes in the earth-atmosphere-cryosphere system, clearly states that changes in the hydrologic cycle are expected, but many questions were left unanswered. In our current climate system, we know the hydrologic cycle is not constant, but is naturally varying from year-to-year. One method for studying future climate scenarios is to examine the variability of the current climate system. If our present day observing systems are sufficiently accurate, we should be able to monitor how changes in one part of the cycle are represented by changes throughout. This, is the goal of this paper - to examine the current day interannual variability in all parts of the hydrologic cycle. Successfully observing consistent changes throughout will suggest that any man-induced changes, including a potential acceleration of the hydrologic cycle could be observed with our present day climate observing systems.

Presented here are both regional and global intercomparisons of the variability in total column water vapor (Randel et al., 1996), atmospheric temperature (Christy et al., 1995), sea surface temperature (Reynolds, 1988), cloudiness (Schiffer et al., 1983, and precipitation (Huffman et al.,1997). The most noticeable event within the time series was the1991 eruption of Mt. Pinatubo. The resulting stratospheric aerosol loading quickly caused a drop in global atmospheric temperature. A concurrent drop in the atmospheric water vapor was observed and is consistent with other observations of SST, cloudiness, and rainfall.