Water and potential evapotranspiration at irrigated and rangeland sites in southern Idaho. Partial research technical completion report

The environment of a weather station site is important in estimating consumptive use by irrigated crops. Consumptive use may be over-estimated when air temperature and vapor pressure data from a weather station with an arid local environment are used without modification. To document the effect of weather station aridity on consumptive use estimates, three sites in irrigated areas and two sites in nonirrigated, arid rangeland in southern Idaho were instrumented with weather stations during 1981. Air temperatures were higher and vapor pressures were lower at the arid sites. Use of air temperatures and dewpoint estimates from arid sites caused an overestimation of ETr by 17 percent (210 mm) over the irrigation season. Results indicate the importance of weather site evaluation and adjustment of siting effects and weather before consumptive use estimates are made. A procedure is outlined for adjusting historical temperature data to reflect an irrigated condition