Centennial Services has been monitoring Et measurements recorded in various Orange County locations for the past 7 years. As previously reported on this website, there has been a widening variance between the CIMIS station 75 (central Irvine) data and the IRWD Central data:

                                1997         1998      1999       2000        2001      2002                                           

        Cimis             53.11       49.48       51.8        50.37       45.71     47.01

         IRWD            48.62       43.87      45.86      46.64       39.1       40.71

% IRWD/CIMIS    91.55%   88.66%   88.53%   92.59%  85.54%  86.60%

Examining the data so far in 2003, however, shows that the gap between these two data sources has closed:

                        Jan 03    Feb 03    Mar 03    Apr 03    May 03  Jun 03      YTD

Cimis              2.51         2.15         3.96        4.64        5.13   Pending   18.39

IRWD             2.36          2.4            3.98       4.54         4.98   Pending   18.26

% IRWD/CIMIS 94.02% 111.63% 100.51% 97.84%  97.08%                 99.29%

The 2003 YTD Et for these two stations is virtually the same.   What has changed?

A comparison of the 2002 data for the same 5 month period reveals that while the data for the CIMIS site is very similar for both years, the IRWD Et increased 13.35% in 2003:

                               Jan           Feb            Mar            Apr            May             YTD

IRWD '02             1.97          3.25          3.22           3.46           4.21              16.11

IRWD '03             2.36          2.4            3.9              4.54          4.98               18.26

%’03/’02      119.80%   73.85%   123.60%   131.21%  118.29%       113.35%

                              Jan           Feb             Mar            Apr            May              YTD

CIMIS '02             2.32           2.58          3.89           4.04           5.2              18.03

CIMIS '03             2.51           2.15          3.96           4.64           5.13            18.39

%’03/’02     108.19%    83.33%   101.80%   114.85%     98.65%      102.00%

As previously noted in this website, the IRWD central weather station’s location is considerably different from the weather station standardization promoted by CIMIS, and is be described as “non-ideal”. “A recent study by the University of California, Davis … . . suggested a scenario in which certain weather parameters can be measured at the “non-ideal” sites and the remaining parameters taken from a nearby CIMIS station” as reported in Water Conservation News October 2002, which went on to say that a statewide feasibility study of this has been undertaken.  See http://wwwdwr.water.ca.gov/ for further information and updates.

 

Given the seeming adjustment in the IRWD Central weather station data we have observed so far this year, is it reasonable to suggest the data is currently being tweaked by insertion of CIMIS data as described above? It will be interesting to continue to compare these two data sets. If IRWD central and CIMIS show ongoing consistency of Et data, would it be reasonable to suggest that IRWD Central customers were possibly under-allocated irrigation water in the past?