Morteza Orang

Survey of Irrigation Methods in California in 2001

AbstractReliable information on irrigation methods is important for determining agricultural water demand trends. The authors have therefore conducted a study over the course of 2011 to collect information on the irrigation methods that were used by growers to irrigate their crops in 2010. The results were compared with earlier surveys to assess trends in cropping and irrigation methods. A one-page questionnaire was developed to collect information on irrigated land by crop and irrigation method. The questionnaire was mailed to 10,000 growers in California who were randomly selected from a list of 58,000 growers by the USDA National Agricultural Statistics Service, excluding rice, dry land, and livestock producers. From 1972–2010, the planted area has increased from 15 to 30% for orchards and from 6 to 15% for vineyards. The area planted with vegetables has remained relatively static, whereas that planted to field crops has declined from 67 to 41% of the irrigated area. The land irrigated with low-volume ...

California Simulation of Evapotranspiration of Applied Water and Agricultural Energy Use in California

Abstract The California Simulation of Evapotranspiration of Applied Water (Cal-SIMETAW) model is a new tool developed by the California Department of Water Resources and the University of California, Davis to perform daily soil water balance and determine crop evapotranspiration (ET c ), evapotranspiration of applied water (ET aw ), and applied water (AW) for use in California water resources planning. ET aw is a seasonal estimate of the water needed to irrigate a crop assuming 100% irrigation efficiency. The model accounts for soils, crop coefficients, rooting depths, seepage, etc. that influence crop water balance. It provides spatial soil and climate information and it uses historical crop and land-use category information to provide seasonal water balance estimates by combinations of detailed analysis unit and county (DAU/County) over California. The result is a large data base of ET c and ET aw that will be used to update information in the new California Water Plan (CWP). The application uses the daily climate data, i.e., maximum (T x ) and minimum (T n ) temperature and precipitation (P cp ), which were derived from monthly USDA-NRCS PRISM data (PRISM Group 2011) and daily US National Climate Data Center (NCDC) climate station data to cover California on a 4 km×4 km change grid spacing. The application uses daily weather data to determine reference evapotranspiration (ET o ), using the Hargreaves-Samani (HS) equation (Hargreaves and Samani 1982, 1985). Because the HS equation is based on temperature only, ET o from the HS equation were compared with CIMIS ET o at the same locations using available CIMIS data to determine correction factors to estimate CIMIS ET o from the HS ET o to account for spatial climate differences. Cal-SIMETAW also employs near real-time reference evapotranspiration (ET o ) information from Spatial CIMIS, which is a model that combines weather station data and remote sensing to provide a grid of ET o information. A second database containing the available soil water holding capacity and soil depth information for all of California was also developed from the USDA-NRCS SSURGO database. The Cal-SIMETAW program also has the ability to generate daily weather data from monthly mean values for use in studying climate change scenarios and their possible impacts on water demand in the state. The key objective of this project is to improve the accuracy of water use estimates for the California Water Plan (CWP), which provides a comprehensive report on water supply, demand, and management in California. In this paper, we will discuss the model and how it determines ET aw for use in water resources planning.

Assessment of Climate Change Impacts on Reference Evapotranspiration and Simulation of Daily Weather Data Using SIMETAW

AbstractIn this study, a SIMulation of EvapoTranspiration of Applied Water (SIMETAW) model was evaluated using monthly climatic data of four stations in Iran, namely Bushehr, Tabriz, Zahedan, and Mashhad, to investigate the effects of climate change on reference evapotranspiration (ETo). SIMETAW generates daily weather data from monthly values applicable in climate change studies. HadCM3 (Hadley Centre Coupled Model ver.3) outputs were statistically downscaled to project future variables. Maximum, minimum, and dew point temperature, precipitation, and wind speed were downscaled under two emission scenarios (A2 and B2) and two future periods (2020–2050 and 2050–2080) to simulate ETo. Calculated ETo values were compared with those simulated by SIMETAW in the base period (1961–2000). Results showed that, except for daily wind speed, the model accurately generated daily temperature variables and monthly precipitation. Furthermore, ETo is expected to increase in most months. Values of ETo at Bushehr Station ar...

SIMETAW# - a Model for Agricultural Water Demand Planning

A successful water management scheme for irrigated crops requires an integrated approach, which accounts for water, soil, and crop management. SIMETAW# is a user friendly soil water balance model that assesses crop water use, irrigation requirements, and generates hypothetical irrigation schedules for a wide range of crops experiencing full or deficit irrigation. SIMETAW# calculates reference evapotranspiration (ETo), and it computes potential crop evapotranspiration (ETc), and the evapotranspiration of applied water (ETaw), which is the amount of irrigation water needed to match losses from the effective soil root zone due to ETc that are not replaced by precipitation and other sources. Using input information on crop and soil characteristics and the distribution uniformity of infiltrated irrigation applications in full or deficit conditions, the model estimates the mean depth of infiltrated water (IW) into each quarter of the field. The impact of deficit irrigation on the actual crop evapotranspiration (ETa) is computed separately for each of the four quarters of the cropped field. SIMETAW# simulation adjusts ETo estimates for projected future CO2 concentration, and hence the model can assess climate change impacts on future irrigation demand allowing the user to propose adaptation strategies that potentially lead to a more sustainable water use. This paper discusses the SIMETAW# model and evaluates its performance on estimating ETc, ETa, and ETaw for three case studies.