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Groundwater level observations due to the lack of synoptic water-level measurements are often available with irregular time intervals. The results lead to an inaccurate understanding of the parameters affecting groundwater level changes and their time delays. This paper presents a simple and low-cost approach to interpolate the irregular, periodic intervals of recorded groundwater level data for the Najafabad aquifer located in central Iran. Forty-six monitoring wells with an average of 20 years of data were used for this study. Piecewise cubic Hermite interpolating polynomial (PCHIP), cubic spline, linear, and nearest neighbor are the selected interpolation methods. Cross-validation with leave-one-out technique was also applied to evaluate the accuracy of the methods under three conditions, including low, average, and high groundwater level decline. The analysis proved that (1) PCHIP interpolation showed a high performance in all of the groundwater level decline conditions (0.22

Drought is one of the natural disasters that causes a great damage to the human life and natural ecosystems. The main differences are in the gradual effect of drought over a relatively long period; impossibility of accurately determining time of the beginning and end of drought; and geographical extent of the associated effects. On the other hand, lack of a universally accepted definition of drought has added to the complexity of this phenomenon. In the last decade, due to increasing frequency of drought in Iran and reduction of water resources, its consequences have become apparent and have caused problems for planners and managers. Therefore, in this study, to investigate severity and duration of meteorological, hydrological and agricultural drought in Karkheh River basin, regional frequency analysis of standardized precipitation index ( SPI ), standardized evapotranspiration index ( SEI ), standardized runoff index ( SRI ) and standardized soil moisture index ( SSI ) was performed using L-moments. Then, using Hosking and Wallis heterogeneity test, basin was divided into four homogeneous areas. After that, based on the Z statistic of goodness-of-fit test for each distribution, the best regional distribution function for each homogeneous region was selected. The results showed that hydrological drought occurs with a very short time delay in Karkheh River Basin after the meteorological drought and two indicators show meteorological and hydrological drought conditions well. Agricultural drought occurs after meteorological and hydrological drought, respectively, and its severity and duration are less than the other indicators. Meteorological, hydrological and agricultural droughts do not occur at the same time in all of the years and in general, the SPI drought Index shows the most severe droughts compared with the other three indices.

The Zayandeh-Rud River basin, Iran, is projected to face spatiotemporally heterogeneous temperature increase and precipitation reduction that will decrease water supply by mid-century. With projected increase (0.70–1.03 °C) in spring temperature and reduction (6– 55%) in winter precipitation, the upper Zayandeh-Rud sub-basin, the main source of renewable water supply, will likely become warmer and drier. In the lower sub-basin, 1.1–1.5 °C increase in temperature and 11–31% decrease in annual precipitation are likely. A system dynamics model was used to analyze adaptation strategies taking into account feedbacks between water resources development and biophysical and socioeconomic sub-systems. Results suggest that infrastructural improvements, rigorous water demand management (e.g., replacing high water demand crops such as rice, corn, and alfalfa), and ecosystem-based regulatory prioritization, complemented by supply augmentation can temporarily alleviate water stress in a basin that is essentially governed by the Limits to Growth archetype

Any change in characteristics of low flows under climate change may have important effects on various socioeconomic, environmental, water resource, and governmental planning aspects. The ai...

The chapter aims to estimate the climate change impacts on the climate variables in Iran’s Zayandeh-Rud River Basin. A multi-model ensemble scenarios framework is used to improve the reliability of the climate change impact assessment by considering the three main sources of uncertainties including uncertainties of GCMs, emission scenarios, and climate variability of daily time series. The probabilistic multi-model ensemble scenarios, which include the 15 GCMs, are used to project the temperature and precipitation for the near future period (2015–2044) under 50% risk level of climate change. In a general view, temperature will rise in the basin while the level of temperature increase varies between. Monthly precipitation changes may be positive or negative in various parts of the basin. Generally, temperature change shows an increasing trend from West to East and has an inverse relationship with height. Nevertheless, the maximum monthly precipitation reduction will occur in winter. This can be of considerable importance for the basin having a semiarid Mediterranean climate in which winter precipitation is the main source of renewable water supply. In a general view, precipitation change shows a decreasing trend from West to East and it has a direct relationship with height. The Zayandeh Rud River Basin has been constantly facing the water stress problem during the past 60 years. Therefore, the results of the climate change impacts on the basin’s climate variables can provide the policy insights for regional water managers to address well the water scarcity in the near future.

Optimal reservoir operation changes and adaptation strategies for the Zayandeh-Rud River Basin's surface water supply system are examined for a changing climate during the 2015–2044 period. On average, the monthly temperature in the basin is expected to increase by 0.46–0.76 °C and annual precipitation is expected to decrease by 14–38% with climate change, resulting in a reduction of the Zayandeh-Rud's peak stream flow and the amplitude of its seasonal range. Snowfall decrease in winter months will generally lead to an 8–43% reduction in annual stream flow under climate change. A reservoir operation model is developed and optimal reservoir operation strategies are identified for adaptation of the basin's surface water supply to climate change in the face of the increasing water demand. Results indicate that the reservoir drawdown season starts 2 months earlier under climate change. Smaller storage levels and greater water releases must occur to meet the increasing water demand. The optimized water release can provide sufficient water for non-agricultural water demand, but agriculture will experience more severe water shortage under a changing climate. Having the highest vulnerability, the agricultural sector should be the main focus of regional management plans to address the current water challenge and more severe water shortages under climate change.

summary Zayandeh-Rud River Basin is one of the most important basins in central Iran, which has been continually challenged by water stress during the past 60 years. Traditionally, a supply-oriented management scheme has been prescribed as a reliable solution to water shortage problems in the basin, resulting in a number of water transfer projects that have more than doubled the natural flow of the river. The main objective of this study is to evaluate the reliability of inter-basin water transfer to meet the growing water demand in Zayandeh-Rud River Basin. A system dynamics model is developed to capture the interrelationships between different sub-systems of the river basin, namely the hydrologic, socioeconomic, and agricultural sub-systems. Results from simulating a range of possible policy options for resolving water shortage problems indicate that water is essentially the development engine of the system. Therefore, supplying more water to the basin without considering the dynamics of the interrelated problems will eventually lead to increased water demand. It is demonstrated that the Zayandeh-Rud River Basin management system has characteristics of the ‘‘Fixes that Backfire’’ system archetype, in which interbasin water transfer is an inadequate water management policy, causing significant unintended sideeffects. A comprehensive solution to the problem includes several policy options that simultaneously control the dynamics of the system, minimizing the risk of unintended consequences. In particular, policy makers should consider minimizing agricultural water demand through changing crop patterns as an effective policy solution for the basin’s water problems.

This study evaluates climate change impacts on crop production and water productivity of four major crops (wheat, barley, rice, and corn) in Iran's Zayandeh-Rud River Basin. Multi-model ensemble scenarios are used to deal with uncertainties in climate change projections for the study period (2015–2044). On average, monthly temperature will increase by 1.1 to 1.5 °C under climate change. Monthly precipitation changes may be positive or negative in different months of the year. Nevertheless, on the annual basis, precipitation will decrease by 11 to 31% with climate change. While warming can potentially shorten the crop growth period, crop production and water productivity of all crops are expected to decrease due to lower precipitation and higher water requirements under higher temperature. Out of the four studied crops, rice and corn are more vulnerable to climate change due to their high irrigation water demand. So, their continued production can be compromised under climate change. This finding is of particular importance, given the locally high economic and food value of these crops in central Iran.