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John Christy on Precipitation


John Christy on Precipitation13-11-2013 16:56
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Dr. John Christy has in his presentation Climate Change Roundtable of 30th May 2013 shown a graph with Wet and Dry percent area for the US.

This graph is part of his internet presentation with a mixed panel (pro and con AGW). The panel who were quizzed on climate change by Rep David McKinley, a Republican congressman from the coal state of West Virginia, consisted of:

Scott Denning............... Colorado State University
Jim Hurrell.....................National Center for Atmospheric Research
Joe Casola.....................Center for Climate and Energy Solutions
Annie Petsonk...............Environmental Defense Fund
Richard Thomas............West Virginia University
Marc Morano................ Climate Depot
Dennis Avery.................Hudson Institute
Myron Ebell...................Competitive Enterprise Institute



There is no indication of how his graphic is supposed to be interpreted. But seen in the context of the whole presentation by Christy, it is clear that this must be interpreted according to Christy as an indication of the failure of the theory of global warming. As shown below the precipitation has become more extreme in line with the theory of global warming. Christy has been less than clear about this in his presentation. However in Written Statement of John R. Christy to Committee on Environment and Public Works 1 August 2012 John Christy has the following remark on page 8:

"As can be seen ......there is a tremendous amount of variability (near zero to near 80 percent), but no long-term trend."


What does the science say ?
With the global warming an increase in precipitation is expected. For some areas, however, there will be a reduction in precipitation. This means more uneven precipitation over certain regions, including the United States.

Here is an extract from IPCC AR4 report concerning precipitation:

Many analyses indicate that the evolution of rainfall statistics through the second half of the 20th century is dominated by variations on the interannual to inter-decadal time scale and that trend estimates are spatially incoherent (Manton et al., 2001; Peterson et al., 2002; Griffiths et al., 2003; Herath and Ratnayake, 2004). In Europe, there is a clear majority of stations with increasing trends in the number of moderately and very wet days (defined as wet days (≥1 mm of rain) that exceed the 75th and 95th percentiles, respectively) during the second half of the 20th century (Klein Tank and Können, 2003; Haylock and Goodess, 2004). Similarly, for the contiguous USA, Kunkel et al. (2003) and Groisman et al. (2004) confirmed earlier results and found statistically significant increases in heavy (upper 5%) and very heavy (upper 1%) precipitation of 14 and 20%, respectively. Much of this increase occurred during the last three decades of the 20th century and is most apparent over the eastern parts of the country. In addition, there is new evidence from Europe and the USA that the relative increase in precipitation extremes is larger than the increase in mean precipitation, and this is manifested as an increasing contribution of heavy events to total precipitation (Klein Tank and Können, 2003; Groisman et al., 2004).


How can this be verified ?
In order to to verify the change in precipitation patterns for the US, I have drawn on the data of the "US Precipitation Moderate - Extreme Wet Percent Area" and "US Precipitation Moderate - Extreme Dry Percent Area based on the Palmer Drought Index databases from the National Climatic Data Center/NESDIS/NOAA..

These figures are shown below in a scattered plot.



It is difficult to draw any conclusions from these graphs without any statistical analysis.

Below the scattered plots of Wet Percent Area, Dry Percent Area and the histograms are shown.



There is a negative correlation between Wet and Dry. They are like a see-saw. If Wet is large there is a trend that Dry is small and reversed. The distribution of Wet and Dry is skewed to the right. This means that some years are extraordinarily wet or some years are extraordinarily dry. One could talk about a wet and dry regime of the US.

The following graph shows the development of Wet Percent Area for the US from January 1895 to June 2013:



There is a significant increasing trend in Wet Percent Area. From January 1895 to June 2013 the expected Wet Percent Area has increased from 20% to 26% corresponding to an increase of 30%.

There is a significant positive correlation, r=0.83 , between two consecutive months of Wet Percent Area. This means there is a reverse see-saw relation between two consecutive months.

Due to the correlation between two consecutive months a prewhitening technique has been used in the estimation and in calculating the confidence intervals.

The following graph shows the development of Dry Percent Area for the US from January 1895 to June 2013:



There is a significant increasing trend in Dry Percent Area. The average Dry Percent Area has increased from 19% in January 1895 to 22% in June 2013 corresponding to an increase 16 %.

There is a significant positive correlation, r=0.86 , between two consecutive months of Dry Percent Area. This means there is a reversed see-saw relation between two consecutive months.

Due to the correlation between two consecutive months a prewhitening technique has been used in the estimation and in calculating the confidence intervals.

In summary there is a significant increase of Moderate - Extreme Wet Percent Area and a significant increase of Moderate - Extreme Dry Percent Area for the years 1895 to 2013. This means that the precipitation has become more extreme.

It seems odd that there has been both an increase in precipitation and in drought conditions; but this is less surprising when one considers that the United States is composed of three main precipitation zones: wet along the West Cost of US and in the East and dry in the West. The wet get wetter and the dry get drier. This is what we see in the statistics. See US participation map.

Summary
As shown above the precipitation has become more extreme in line with the theory of global warming.

Christy has been less than clear about this in his presentation.

I am sure that he is more than competent to interpret and explain the reports on precipitation from the IPCC AR4, so it surprises me that he does not appear to give the complete picture on the growing extremes of precipitation in the US. This is disappointing: He owes us a better effort.

For the most recent research please look into NASA Warming Driven Changes in Global Rainfall and NOAA home page..

However, I would like to thank Christy to show the mentioned graph from NOAA, giving me an opportunity to clarify how this graph should be interpreted. I would remind Christy to bring the full picture about precipitation in his next presentation.
Join the debate John Christy on Precipitation:

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