Impact of climate change on potential evapotranspiration (case study: west and NW of Iran)

• Published in: Theoretical and applied climatology Vol. 136; no. 1-2; pp. 185 - 201
• Main Authors: Dinpashoh, Y., Jahanbakhsh-Asl, S., Rasouli, A. A., Foroughi, M., Singh, V. P.
• Format: Journal Article
• Language: English
• Published: Vienna Springer Vienna 01.04.2019; Springer; Springer Nature B.V
• Subjects: Analysis; Aquatic Pollution; Atmospheric Protection/Air Quality Control/Air Pollution; Atmospheric Sciences; Case studies; Climate change; Climate science; Climatology; Earth and Environmental Science; Earth Sciences; Environmental impact; Evapotranspiration; Global temperature changes; Irrigation; Irrigation (Agriculture); Irrigation requirements; Methods; Original Paper; Potential evapotranspiration; Slope; Slopes; Stations; Time series; Trend analysis; Trends; Waste Water Technology; Water Management; Water Pollution Control; Iran
• DOI: 10.1007/s00704-018-2462-0
• ISSN: 0177-798X

Potential evapotranspiration (ET 0 ) is one of the main elements when computing agricultural irrigation requirements and scheduling. All climatic parameters as well as ET 0 are influenced by climate change. The aim of this study is trend analysis of monthly and annual ET 0 time series in the west and NW of Iran. Values of ET 0 are estimated at 36 selected stations, using the FAO-56 Penman-Monteith (FAO-56 PM) method. Then, the non-parametric Mann-Kendall (MK) method was used to detect trends. The slopes of trend lines are estimated using Sen’s estimator approach. Results showed that about 86%of the monthly ET 0 time series had upward trends of which 35.6 and 43% were significant at 0.01 and 0.05 levels, respectively, 47.4% exhibited a significant upward trend at the 10% level. In contrast, less than 0.7% of the whole monthly ET 0 time series showed a significant downward trend ( α  < 0.01). Only 1.1% of the monthly ET 0 time series had significant downward trends ( α  < 0.10). The strongest positive upward trend (significant at the 0.01 level) was detected in August at the Kermanshah station. However, the strongest negative downward trend belonged to the Khodabandeh station. The steepest upward and downward monthly ET 0 slopes were observed at Maragheh and Khodabandeh stations. The magnitude of trends for these two stations are estimated as 2.33 and − 2.01 mm/year, respectively. On an annual timescale, above 94% of the stations had upward trend slopes. About 67% of the total stations exhibited significant trends at the 10% level. Very few sites (2.7%) showed downward annual ET 0 trends ( α  < 0.10). At the annual scale, the first three strongest upward trends belonged to the Kermanshah, Urmia, and Tabriz stations, respectively ( α  < 0.01). It can be concluded that ET 0 in the west and NW of Iran have an increasing trend for most of the stations. Therefore, it is important to use water in a prudent manner in this area.