UPDATED PROCEDURES FOR CALCULATING STATE-WIDE CONSUMPTIVE USE IN IDAHO

摘要

Evapotranspiration and net irrigation water requirements were determined for 123 weatherrnstation locations across the state of Idaho for available periods of record. Estimates were madernfor daily, monthly and annual timesteps. Updated methods were employed for calculatingrnreference evapotranspiration (ET_r) and crop coefficients (K_c). The ET estimates cover a widernrange of agricultural crops grown in Idaho and, in addition, ET estimates have been made for arnnumber of native plant systems including wetlands, rangeland, and riparian trees. Estimates havernbeen made for evaporation from three types of open water surfaces ranging from deep reservoirsrnto small farm ponds. The ET and net irrigation water requirement calculations are intended forrnuse in design and management of irrigation systems, for water rights management andrnconsumptive water rights transfers and for hydrologic studies. ET calculations have been madernfor all times during the calendar year including winter to provide design and operationrninformation for managing land application of agriculture, food processing and other wasternstreams. The weather stations evaluated include 107 National Weather Service (NWS)rncooperative stations measuring primarily air temperature and precipitation and 16 AgriMetrnagricultural weather stations. The AgriMet stations measure a full compliment of weather datarnaffecting evapotranspiration and are located primarily in the southern part of the state. Estimatesrnat many stations cover more than 80 to 100 year periods of air temperature data. Because onlyrnmaximum and minimum air temperature are observed at the NWS cooperative stations, the solarrnradiation, humidity and wind speed data parameters required in the ASCE Penman-Monteithrnequation (ASCE-PM) were estimated similar to recommendations in ASCE-EWRI (2005) wherernestimates for solar radiation (R_s) were based on differences between daily maximum andrnminimum air temperature and estimates for daily dewpoint temperature were based on dailyrnminimum air temperature. Estimates for wind speed were based on long-term mean monthyrnsummaries from AgriMet stations in southern Idaho and some airport locations in central andrnnorthern Idaho. Crop evapotranspiration, abbreviated ET_c, was calculated on a daily timesteprnbasis for improved accuracy. Daily calculation timesteps allowed for the calculation ofrnevaporation of water from wet soil surfaces following precipitation or irrigation events. ET_c forrnmonthly, growing season and annual periods were summed from the daily calculations. Basalrncrop coefficient curves were developed or organized for 42 crop and land-cover types.rnScheduling of irrigations was simulated to estimate soil evaporation from irrigation wettingrnevents using a root-zone water balance.