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intervenes. We thus focus on the Supreme Court, which can be systematically compared
across the different river basins with high reliability because Supreme Court decisions are
a matter of public record.
Water Supply. We utilize precipitation as a general measure of supply. The measure that
is employed in the analysis reported in this paper measures precipitation at the location in
the state that has the longest series of observations. These observation stations are not
always located in the most populous areas or the political centers of each state. The
advantage of this measure is that in most states, precipitation data is available for at least
one station back to 1900 or 1901. The disadvantage is that this location may not
accurately represent the environmental stress being placed on the area of interest, which
is the area near the river in question.
To get the specific measure that is used in the analysis, the original data was
transformed into inches of rainfall. The yearly rainfall totals for both states in the dyad
were then added together. This yields a measure of total water supply available to the
dyad. Although the measure can be driven by one state’s abundance or scarcity of water,
we believe that this does a good job of capturing a dyad’s water stress. The data was
obtained from the United States Historical Climatology Network
5
.
Dyadic Population Change. The measure of population is taken from U.S. census data.
The census is taken every ten years. The years between the censuses were interpolated
for each state. The total population for each state in any given year was summed to
5
Data is available at http://cdiac.esd.ornl.gov/epubs/ndp019/ndp019.html.
Convention