Lake Urmia in northwest Iran, once one of the largest hyper saline lakes in the world, has shrunk by almost 90% in area and 80% in volume during the last four decades. To improve the understanding of regional differences in water availability throughout the region and to refine the existing information on precipitation variability, this study investigated the spatial pattern of precipitation for the Lake Urmia Basin. Daily rainfall time series from 122 precipitation stations with different record lengths were used to extract 15 statistical descriptors comprising 25 th percentile, 75 th percentile, and coefficient of variation for annual and seasonal total precipitation. Principal component analysis in association with cluster analysis identified three main homogeneous precipitation groups in the lake basin. The first sub-region (Group-1) includes stations located in the center and southeast, the second sub-region (Group-2) covers mostly northern and northeastern part of the basin, and the third sub-region (Group-3) covers the western and southern edges of the basin. Results of principal component (PC) and clustering analyses showed that seasonal precipitation variation is the most important feature controlling the spatial pattern of precipitation in the lake basin. The 25 th and 75 th percentiles of winter and autumn are the most important variables controlling the spatial pattern of the first rotated principal component explaining about 32% of the total variance. Summer and spring precipitation variations are the most important variables in the second and third rotated principal components, respectively. Seasonal variation in precipitation amount and seasonality are explained by topography and influenced by the lake and westerly winds that are related to the strength of the North Atlantic Oscillation. Despite using incomplete time series with different lengths, the identified sub-regions are physically meaningful.

The natural flow regime of rivers has been strongly altered worldwide , resulting in ecosystem degradation and lakes drying up, especially in arid and semi-arid regions. Determining whether this is due mainly to climate change or to water withdrawal for direct human use (e.g. irrigation) is difficult, particularly for saline lake basins where hydrology data are scarce. In this study, we developed an approach for assessing climate and land use change impacts based on river flow records for headwater and lowland reaches of rivers, using the case of Lake Urmia basin, in north-westen Iran. Flow regimes at upstream and downstream stations were studied before and after major dam construction and irrigation projects. Data from 57 stations were used to establish five different time intervals representing 10 different land use development periods (scenarios) for upstream (not impacted) and downstream (impacted) systems. An existing river impact (RI) index was used to assess changes in three main characteristics of flow (magnitude, timing and, intra-annual variablity). The results showed that irrigation was by far the main driving force for river flow regime changes in the lake basin. All stations close to the lake and on adjacent plains showed significantly higher impacts of land use change than headwaters. As headwaters are relatively unaffected by agriculture, the non-significant changes observed in headwater flow regimes indicate a minor effect of climate change on river flows in the region. The benefit of the method developed is clear interpretatation of results based on river flow records, which is useful in communicating land use and climate change information to decision makers and lake restoration planners.

14Saline lakes have diminished considerably due to large-scale irrigation projects throughout the 15 world. Environmental flow (EF) release from upstream reservoirs could help conserve and 16 restore these lakes. However, experiences from regions lacking environmental legislation or 17 with insufficient water resources management show that, despite EF allocation, farmers tend 18 to use all available water for agriculture. In this study, we employed a new method for 19 designing environmental flow release strategies to restore desiccated terminal lakes in arid and 20 semi-arid regions with intensive cultivation within the catchment. As a novelty, the method 21 takes into account farmers' water use behavior, return flow from irrigation, interaction with 22 groundwater, evaporation together without considering any detail of each and natural flow 23 regime in upstream systems to design an optimum monthly EF release strategy for reservoirs. 24 We applied the method to the water resource system of Lake Urmia, once the largest saline 25 lake in the Middle East and now one of the most endangered saline lakes in the world. The 26 analysis showed that the EF released is exploited by lowland farmers before reaching Lake 27 Urmia and that inflow to the lake from some rivers has decreased by up to 80%. We propose a 28 new EF release strategy that requires a considerable change in practice whereby water is 29 released in the shortest possible time (according to reservoir outlet capacity) during the period 30 of lowest irrigation demand in winter. Restoring the lake to minimum ecological level would 31 require 2.4-3.4 km 3 EF allocation by different methods of release based on the recent condition 32 (2002-2011) of the lake.33 34

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The spatial patterns of precipitation regarding physiography and atmospheric circulations in the Lake Urmia Basin have been investigated. Daily rainfall time series for the 50 most reliable precipitation stations for the period 1980-2010 were analyzed to detect the regional precipitation pattern. To identify rainfall homogeneous regions, principal component analysis was applied to the precipitation dataset. Agglomerative hierarchical clustering analysis using the Ward and Euclidean distance methods revealed three distinctive precipitation regions in the basin influenced by topography and lake. The first region (G1) covers the north and northeastern part of the Lake Urmia. G2 includes stations located in south and southeastern part of the basin, while G3 covers the western part of the lake basin. The results from this study can be used to better plan agricultural land use, cropping patterns and water management in the delineated homogeneous rainfall regions.

<p>Water, energy, and food security in today's world have been hampered by high population and economic growth, pressures on limited resources, and climate change. Accordingly, balancing the various critical components of biomass in the form of a water-energy-food (WEF) Nexus approach is one of the essential pillars of water resources management, which will enhance the long-term sustainability of water resources by promoting sustainable development. Assessing the WEF Nexus based on CO<sub>2</sub> emissions leads to quantify the role of each component of WEF. This work aims to quantify WEF Nexus in a pilot study in the North West of Iran based on analyzing the CO<sub>2</sub> emission of the involved sectors. Gathering all require data that are involved in different activities in water, energy, and food sectors is the main challenge in this regard. Sahand Agro-Industry CO<sub>2</sub>, established in 1996 and expanded in an area about 200 ha to produce alfalfa, maize, potato, rapeseed, sugar beet, and wheat. The area with an average annual temperature of 10.1 °C and bout 356 mm precipitation is located in a warm, dry-summer continental climate (Dsb climate, according to köppen climate classification). A detailed dataset including labor, machinery, diesel oil, fertilizer (nitrogen, potassium, and phosphorus), biocide (pesticide, fungicide, and herbicide), irrigation water (groundwater and surface water), and output per unit area per product has been collected for 2008-2017. We evaluated the WEF Nexus by estimating CO<sub>2</sub> emission based on the water and energy equivalent and food production per unit area of crop production systems. In this regard, we applied several indices, including the WEF Nexus, water, and energy consumption, mass, and economic productivity, to estimate the CO<sub>2</sub> emitted during a ten-year time period, besides the effect of changing the cropping pattern on the amount of CO<sub>2</sub> emission. Furthermore, we developed an approach to achieve optimal cropping pattern to minimize water and energy consumption and maximize productivity. Because of the detail calculation of mentioned indices and existing operational limitations, first, two margin scenarios were developed: 1- crop pattern with the lowest CO<sub>2</sub> emission and 2- Crop pattern with the maximum net benefit. For each pattern, we calculated the area for different crops. Then by combining these two marginal patterns and using dynamic programming, we developed 128 different patterns between the two mentioned margins. The results showed that as the differentiation in the amount of CO<sub>2</sub> equivalent for each crop, different cultivation patterns would have a different effect on the carbon dioxide emission. Water withdrawal (extraction, displacement, and distribution of water in the field) requires energy consumption, which varies depending on the source used for irrigation. Also, water productivity per kcal per m<sup>3</sup> will vary depending on the type of crop, cropping system, and agricultural management. Finally, we clustered scenarios based on CO<sub>2</sub> emission and net benefit and suggested the optimum condition.</p><p>Keywords: CO<sub>2</sub> emission, economic productivity, optimization, sustainable development, water-energy-food Nexus</p>

<p>Arctic rivers’ flow regime has changed under climate change and its consequences on melting glaciers, thawing permafrost, and precipitation patterns. Reservoirs, hydro-power sites, and water diversions have also changed flow regimes in the Arctic. The flow regime alteration in the Arctic rivers has a strong influence on the conservation and sustainability of the native biodiversity of the riverine ecosystem. The main objective of this paper is to evaluate changes in the (1) magnitude of monthly stream flows, (2) magnitude and duration of annual maxima and minima flows, (3) timing of annual maxima and minima, (4) frequency and duration of high and low pulses, and (5) rate and frequency of daily flows in seven major Arctic Rivers. The analyses provide an important basis to characterize and understand the influence of climate change and anthropogenic activities on the flow regimes in the Arctic. Streamflow observations were obtained from the outlet of the Lena, Yenisei, Kolyma, Ob (Russia), Yukon (USA and Canada), Mackenzie (Canada), and Tana (Norway and Finland) rivers in this study. These rivers are main freshwater suppliers for Arctic Ocean. Of these, five have been regulated and two are considered pristine rivers. In addition, the impact of 16 reservoirs on flow regime in the headwaters and tributaries of Lena, Yenisei, Mackenzie, and Kolyma were evaluated. The annual flow showed an increasing trend in all rivers and with a statistically significant level in Yenisei, Lena, and Mackenzie. Our results also indicated that changes in the observed flow regimes at the outlet stations vary from low to incipient level. Out of 16 reservoirs that were analyzed for flow regimes changes, construction of Krasnoyarsk and Shushenskaya dams on the Yenisei River showed the highest impact on flow regime and flow regime alteration was classified as severe in this river.</p>