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Title: Testing gridded NWS 1-Day observed precipitation analysis in a daily irrigation scheduler

Author
item SASSENRATH, G - Kansas State University
item Schneider, Jeanne
item SCHMIDT, A - University Of Nebraska
item Corbitt, Jason
item Halloran, John
item PRABHU, R - Mississippi State University

Submitted to: Agricultural Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/16/2013
Publication Date: 12/5/2013
Citation: Sassenrath, G.F., Schneider, J.M., Schmidt, A.M., Corbitt, J.Q., Halloran, J.M., Prabhu, R. 2013. Testing gridded NWS 1-Day observed precipitation analysis in a daily irrigation scheduler. Agricultural Sciences. 4(12):621-627.

Interpretive Summary: One of the inputs required by daily irrigation schedulers is the amount of water supplied by rainfall. In-field measurements of daily precipitation are expensive or laborious, while measurements from gauges within a few kilometers are frequently not representative due to the high spatiotemporal variability of precipitation. Online radar-based precipitation analyses from NOAA’s National Weather Service (NWS) have obvious potential to provide the needed data, but are known to have varying degrees of accuracy with location and conditions. The NWS precipitation analysis is computed on a 4 km x 4 km grid, so differences should also be expected between the product and individual gauge measurements under each grid cell. In order to test the utility of the NWS precipitation analysis in a daily irrigation scheduler, daily data were gathered in July 2012 from 18 weather stations under 2 NWS precipitation analysis grid cells across instrumented research and production fields in the Mississippi Delta. Differences between individual station measurements and the NWS precipitation analysis are examined, and root-zone daily soil water deficits computed using both station data and the NWS precipitation analysis. Sub-grid spatial variability between gauge locations, and differences in precipitation between gauges and the gridded NWS analysis, are found to be similar to those reported elsewhere. Differences between time series of soil water deficit computed using the two different precipitation data sources are noted, but prove to be of limited impact on the decision to irrigate or not irrigate. It is also noted that profile-filling rainfalls limit the impact of accumulating error, resetting the modeled soil water to “full”. Given the Delta-local practice of irrigating to refill the soil water profile, use of the NWS daily precipitation analysis data as input for a daily irrigation scheduler is judged not only acceptable, but preferable to other sources of daily precipitation data.

Technical Abstract: One of the inputs required by daily irrigation schedulers is the amount of water supplied by rainfall. In-field measurements of daily precipitation are expensive or laborious, while measurements from gauges within a few kilometers are frequently not representative due to the high spatiotemporal variability of precipitation. Online radar-based precipitation analyses from NOAA’s National Weather Service (NWS) have obvious potential to provide the needed data, but are known to have varying degrees of accuracy with location and conditions. The NWS precipitation analysis is computed on a 4 km x 4 km grid, so differences should also be expected between the product and individual gauge measurements under each grid cell. In order to test the utility of the NWS precipitation analysis in a daily irrigation scheduler, daily data were gathered in July 2012 from 18 weather stations under 2 NWS precipitation analysis grid cells across instrumented research and production fields in the Mississippi Delta. Differences between individual station measurements and the NWS precipitation analysis are examined, and root-zone daily soil water deficits computed using both station data and the NWS precipitation analysis. Sub-grid spatial variability between gauge locations, and differences in precipitation between gauges and the gridded NWS analysis is found to be similar to those reported elsewhere. Differences between time series of soil water deficit computed using the two different precipitation data sources are noted, but prove to be of limited impact on the decision to irrigate or not irrigate. It is also noted that profile-filling rainfalls limit the impact of accumulating error, resetting the modeled soil water to “full”. Given the Delta-local practice of irrigating to refill the soil water profile, use of the NWS daily precipitation analysis data as input for a daily irrigation scheduler is judged not only acceptable, but preferable to other sources of daily precipitation data.