Estimation of effective precipitation for winter wheat in different regions of Iran using an Extended Soil-Water Balance Model

Abstract

Estimated Effective Precipitation (Pe) in dryland areas is an essential element of water resource management. It<br />represents the amount of precipitation available in the crop root zone to meet the needs of evapotranspiration. The<br />current study compared different approaches for estimating Pe in different climatic zones of Iran. A two-layer soil–<br />water balance (SWB) model was adopted based on the proposed approach in which a portion of the previous day's<br />precipitation saved between the previous and current root-zone development is added to the Pe of the current day. To<br />this end, we used three groups of data (meteorological, phenological, and soil characteristics data) related to 21 agrometeorological<br />stations representing arid, semi-arid, semi-humid, and humid regions of the country. The results of<br />this study indicated that, in spite of data limitations, the new procedure performed appropriately in estimating that<br />part of the wheat yield which could be explained by Pe only. Coefficients of determination (R2) between annual<br />precipitation and Pe ranged from 0.50 in the humid climatic zone to 0.82 in the arid climatic zone. Ultimately, using<br />annual precipitation data collected from 181 Iranian synoptic stations and its correlation with Pe, the first annual Pe<br />map of Iran was produced.<br />