Not sure how I missed this one last year but here it is now staring me in the face. I thought some of you would find this interesting. Yet another possible role aerosols play in our atmosphere. Coupled with the prejected precipitation changes California faces in global warming scenarios this new information is making things look much worse. Quote: Physical / Statistical and Modeling Documentation of the Effects of Urban and Industrial Air Pollution in California on Precipitation and Stream Flows Introduction Most climate change investigations focus on the role of greenhouse gases in global warming and on the role of minute particles in the atmosphere (atmospheric aerosols) that cool the atmosphere by reflecting some of the incoming solar radiation back to space. Atmospheric aerosols were thought to counterbalance global warming; however, this is not their only role. Recent research, funded by the California Energy Commission with Dr. Daniel Rosenfeld and Dr. William Woodley along with their research team, focused on California-specific analysis that indicates atmospheric aerosols can also impede rain and snow formation in the Sierra Nevada Mountains. This study showed that high concentrations of extremely small (submicron) cloud condensation nuclei (CCN) aerosols (on which atmospheric water can form) slow the formation of raindrops and ice, which delays the conversion of cloud water into precipitation. This effect is exhibited in different ways in clouds – either strengthening deep convective clouds or suppressing the amount of precipitation from shallow clouds around mountains (orographic clouds). These short-lived orographic clouds are the most common in the winter on the west coast and are formed as air is forced upward when passing over barriers such as mountains. California’s annual precipitation losses over the mountains are projected at 10 to 25 percent, presumably because of the pollution aerosols that are transported from urban and industrial areas. Full article and link to the 172page report (Energy.CA.Gov)
Very interesting, I'd never thought of it that way either. It does seem like they've had their share of floods, lately, though, but that doesn't mean that total rainfall couldn't be lower than before.
True, our floods occur for multiple reasons. Reasons can include habitat destruction and paving over with concrete and asphalt which sheets water off into ditches and sewer drainages instead of absorbing, slowing, and sinking the water like a natural grassland would. Snowpack melting too quickly and in one quick pulse has also been a reason for catestrophic flooding and is anticipated to be a major issue in a future affected by global warming (if projections hold true). So even with less average precipitation flooding events can increase.
Yeah, the dry ground doesn't absorb water as readily and so overland flow is more pronounced. Of course, saturated soil doesn't absorb much either, but for different reasons.
Here is a corrected link to the article mentioned in the inital posting: PIER PROJECT REPORT - Publication # CEC-500-2007-019
