In addition to changes in global average precipitation, some have argued there could be more pronounced changes in the characteristics of regional and local precipitation due to global warming. For example, Trenberth et al. (2003) hypothesized that, on average, precipitation will tend to be less frequent, but more intense when it does occur, implying greater incidence of extreme floods and droughts, with resulting consequences for water storage. Their arguments are based on the premise that local and regional rainfall rates greatly exceed evaporation rates and thus depend on the convergence of regional to continental scale moisture sources. They surmise that rainfall intensity should increase at about the same rate as the increase in atmospheric moisture, namely 7 percent per degree Celsius with warming. This means that the changes in rain rates, when it rains, are at odds with the 1–2 percent per degree Celsius model estimates for total rainfall amounts as discussed previously. The implication is that there must be a decrease in light and moderate rains, and/or a decrease in the frequency of rain events, as found by Hennessey et al. (1997). Thus, the prospect may be for fewer but more intense rainfall – or snowfall – events.