Modeling Spatio-Temporal Changes in Evaporation Using Class A Pan Evaporation Data: Presenting a Novel Approach for Use in Dynamic and Distributed Models of Rainfall-Runoff

Document Type : Research

Authors

1 PhD. Student of Watershed Science and engineering, Faculty of Natural Resources, Department of Reclamation of Arid and Mountainous Region, University of Tehran, Tehran, Iran.

2 Faculty. Department of natural resources. University of Tehran

3 university of tehran

10.22092/wmrj.2023.362586.1544

Abstract

Extended Abstract
Introduction and Objective
Evaporation is one of the important parameters in hydrology that plays a significant role in the water cycle. The aim of this research is to present a new approach for spatio-temporal modeling of evaporation changes, which can be used in rain-runoff models.
Materials and Methods
In order to carry out this research, monthly evaporation data over a 20-years period (2002-2021) were used from the Maroun evaporation monitoring station located in the Paskouhak catchment, 27 kilometers west of Shiraz, as well as three stations surrounding Paskouhak catchment including Shiraz, Ghalat, and Dasht Arjan stations. Initially, by using regression modeling and determining the relationship between evaporation and elevation above sea level for each month, monthly evaporation raster maps were drawn for the study area. Then, using the proposed approach of using the ratio equations method, the initial spatio-temporal model of evaporation changes was prepared. Due to the dynamic nature and sensitivity of the evaporation parameter, the impact of various factors on the intensity of evaporation was simulated and the initial raster maps were corrected to a large extent. For this purpose, correction coefficients obtained in the form of raster maps or numerical coefficients were used. These coefficients included the correction coefficient of evaporation intensity due to the ratio of water depth at the target surface to the water depth in the evaporation pan, the effect of different days of the year on the conversion coefficient of the evaporation pan, and the correction coefficient based on changes in elevation from the ground surface. All stages of the research were performed in the SNAP and MATLAB programming environments and their graphical display in the ArcGIS environment.
Results and Discussion
The results showed that using the linear regression model and elevation parameters above sea level, it is possible to obtain the spatial distribution of evaporation with high accuracy (R2=0.81 in December and R2=0.99 in March and October) in the form of a regular pixel grid (in this study 100 square meters). In addition, the final spatio-temporal distribution model of evaporation showed that there is a noticeable difference between the results of the initial and the final evaporation models in some areas of the study region (pixels). This highlights the need for more corrective coefficients.
Conclusion and Suggestion
Therefore, using the proposed approach in this study, it is possible to model the changes and spatio-temporal distribution of evaporation as three-dimensional time series matrices (longitude, latitude, time) with a time scale corresponding to the evaporation monitoring station in the study area.

Keywords

Main Subjects

Watershed Management Research Journal

Articles in Press, Accepted Manuscript
Available Online from 21 September 2023

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History

  • Receive Date: 13 June 2023
  • Revise Date: 18 August 2023
  • Accept Date: 21 September 2023

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