In this study, a comprehensive trend analysis was employed to study the spatiotemporal changes in precipitation characteristics with an increased temperature, as well as over time. The nonparametric Mann–Kendall test and the quantile regression methods were applied to detect the plausible temporal trends in 11 extreme rainfall indices and three temperature indices employed in this study. The results showed there was little evidence to suggest that increases in the maximum of 3-h and 24-h precipitation at higher temperatures resulted in similar increases in the annual precipitation, with most stations throughout Iran showing drying features with higher temperatures. Generally, most regions over Iran scaled negatively, implying a reduction in the annual precipitation ranging from −2.64 to −0.44 mm/°C at higher temperatures. The linear tendencies of the maximum 24-h precipitation ranged from −0.4 to 0.23 mm/°C. The annual precipitation of the stations located at Urmia Lake, Caspian Sea, and the Eastern Border Basins showed a decreasing trend (−3.70 to 1.11 mm/year), while the number of rainy days increased (−2.78 to 4.72), which showed the occurrence of lighter rainfall in these regions. The increasing trend in the maximum 24-h precipitation over Western and Central Iran implied a higher probability of extreme precipitation with a higher intensity. This study revealed that the shift in precipitation extremes shifted from fall to winter by increasing the elevation, but these effects have no statistical significance in Iran.
Extended periods of hydro-climate extremes with excessive or scarce rainfall associated with high or low temperatures have resulted in an imbalanced water cycle and inefficient socio-economic systems in several regions of Iran. However, there is a lack of comprehensive investigations on short-term to long-term variations in timing, duration, and temperature of wet/dry spells. This study bridges the current gap through a comprehensive statistical analysis of historical climatic data (1959–2018). Results indicated that the negative tendency of the accumulated rainfall (− 0.16/ − 0.35 mm/year during the past 60/30 years) in 2- to 6-day wet spells had made significant contributions to the ongoing downward trend in annual rainfall (− 0.5/ − 1.5 mm/year during the past 60/30 years) owing to a warmer climate condition. Warmer wet spells are likely responsible for precipitation patterns changes in snow-dominated stations since their wet spells temperature has more than threefold growth with increasing distance to coasts. The most detected trends in climatic patterns have started in the last two decades and become more severe from 2009 to 2018. Our results confirm the alteration of precipitation features across Iran due to anthropogenic climatic change, and suggest expected increase in air temperature would likely result in further dry and warm conditions over the coming decades.
Water scarcity and lack of soil fertility are two major problems in the agriculture sector. This study aimed to use Azolla anzali and Lemna minor as a cover for a free surface of the water since not only do they have the potential to reduce evaporation, but they can also produce green fertilizer. Therefore, a completely randomized design experiment with 4 treatments (Azolla anzali, Lemna minor, combination of Azolla anzali+ Lemna minor and control) was performed with three replications. The surface of the reservoirs was covered with the mentioned plants and the changes in water height were measured every other day and the amount of nutrients (nitrogen and phosphorus) of the plant tissue was measured three times at the beginning, middle, and end of the period. Eventually, water loss in tanks containing Lemna, Azolla, and Lemna+ Azolla, was 39, 33.2, and 28.7% less than the control tank. The highest amount of nutrients in plant tissue was observed in Lemna, Azolla+ Lemna, and Azolla treatments, respectively. Although the amount of nutrients in the combined treatment was not higher than that of Lemna more biomass was produced, which means it can provide more fertilizer. Finally, the combined treatment of the two plants is a more suitable option to be used.
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