WDC018: Meteorological and Climate Data to Support ET-Based Irrigation Scheduling, Water Conservation, and Water Resources Management
Statement of Issues and JustificationStatement of Issue and Justification
Although the need for multistate coordination of irrigation water resources has always existed, recent droughts and a major population expansion in many western states has made this coordination even more imperative. Irrigated agricultural acreage is on the decline in many areas of the Western U.S., but it is still an important producer and the major user of water in most western states, where it is estimated that 90% of the freshwater drawn from well and surface sources is used for agriculture.
Irrigation scheduling models that have been developed to assist growers to estimate when and how much irrigation water to apply to their crops. Most, if not all, scheduling models use weather or climate data, which are commonly produced and disseminated by state or regional personnel. The data formats, however, vary by location, and local irrigation scheduling models only utilize local data. Data differences include time steps (hourly vs. daily), weather parameter order, and level of quality control. Clearly, there exists a need to coordinate weather data collection, storage formats, and data quality control in addition to sharing scheduling models.
Crop evapotranspiration (ETc) is commonly estimated by first calculating standardized reference evapotranspiration (ETref), which accounts for the weather influence on evaporative demand. Then, the ETref is multiplied by a crop coefficient (Kc) factor to estimate ETc. The ASCE-EWRI committee developed unique equations to estimate ETref for a short reference canopy (ETo) and for a tall reference canopy (ETr). Both equations are modifications of a version of the Penman-Monteith equation (ASCE-EWRI, 2005, Allen et al. 1998). Because new equations are used for ETref, questions have arisen about the accuracy of existing Kc factors. It is desirable to standardize Kc development and to find methods to make Kc values more universally applicable. During the period of the recent WERA-202 coordinating committee, a methodology to convert Kc values for use with ETo and ETr was developed. However, Kc values also vary with the cli-mate, irrigation system, and irrigation frequency, so further research/coordination is needed. There exist many varying methods used regionally and from state to state to address ET-based irrigation scheduling.
Irrigation scheduling models vary farm-to-farm, state-to-state, and region-to-region. There is need to coordinate, discuss, and review these models to improve and standardize methodologies and to provide clientele with the best possible information for irrigation management. One ex-ample of the need for better irrigation scheduling information and methods is the Environmental Quality Incentive Program (EQIP) program offered through the USDA Natural Resource Con-servation Service (NRCS). This program has begun providing cost-share money to producers to improve their irrigation water management. To be paid, the producers have to show documenta-tion of irrigation water management for the entire growing season. This has created a demand for irrigation water management training for producers and NRCS staff. These demands have further increased the need for accurate crop specific water use estimates.
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