Trend analysis of evapotranspiration applying parametric and non-parametric techniques (case study: arid regions of southern Iran)

Evapotranspiration, as the main component of the hydrologic cycle, will affect plant water demands and water resources plan. The aims of present research were to evaluate the tendency in reference evapotranspiration (ET₀) by the Mann–Kendall test, the Spearman’s Rho test and the linear regression analysis at the 5% significant level using meteorological data of 16 synoptic stations at Southern Iran during period 1980–2010. Results revealed that 1, 3, 6, and 12 monthly ET₀ in most regions of study area showed increasing trends. Only, Shiraz station exhibited the significant decreasing trend in all time scales based on statistical methods. The values of the significant raising tendencies in annual ET₀ varied among − 0.501 at Shiraz and + 3.194 mm/year at Bam. Based on seasonal time scale, also Bam station showed the maximum significant increasing tendency (in summer and spring) based on Mann–Kendall and Spearman’s Rho techniques. The monthly analysis of trend in ET₀ series indicated that the highest amounts of stations with significant increase tendency discovered in May. In general, this study result indicates a serious warning about warming and climate change of southern Iran. This subject can cause different effects including increment of water consumption in agricultural sector, increase of water rain waste, enhancement of water waste in dams, reservoirs, lakes, etc., decrease of surface water quality, and food crisis.