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Water and water management are no longer related to environmental studies. There is a very strong link between water and a state's security, as well as its survival and development. A decline in water availability may lead to a collapse or even the extinction of a whole civilization. Sometimes referred to as a "water‐bankrupt" state, Iran is a case that underlines the close relation between water and security, from the perspective of survival and opportunities for development. Without a doubt, the Islamic Republic of Iran is among those countries that are the most affected by climate change and low water levels. The main goal of this paper is to analyze challenges related to water in Iran, including the political, security, economic, and social dimensions. [ABSTRACT FROM AUTHOR]

Global warming intensifies the hydrological cycle by altering the rate of water fluxes to and from the terrestrial surface, resulting in an increase in extreme precipitation events and longer dry spells. Prior hydrological intensification work has largely focused on precipitation without joint consideration of evaporative demand changes and how plants respond to these changes. Informed by state‐of‐the‐art climate models, we examine projected changes in hydrological intensification and its role in complicating water resources management using a framework that accounts for precipitation surplus and evaporative demand. Using a metric that combines the difference between daily precipitation and daily evaporative demand (surplus events) and consecutive days when evaporative demand exceeds precipitation (deficit time), we show that, globally, surplus events will become larger (+11.5% and +18.5% for moderate and high emission scenarios, respectively) and the duration between them longer (+5.1%; +9.6%) by the end of the century, with the largest changes in the northern latitudes. The intra‐annual occurrence of these extremes will stress existing water management infrastructure in major river basins, where over one third of years during 2070–2100 under a moderate emissions scenario will be hydrologically intense (large intra‐annual increases in surplus intensity and deficit time), tripling that of the historical baseline. Larger increases in hydrologically intense years are found in basins with large reservoir capacity (e.g., Amazon, Congo, and Danube River Basins), which have significant populations, irrigate considerable farmland, and support threatened and endangered aquatic species. Incorporating flexibility into water resource infrastructure and management will be paramount with continued hydrological intensification. Plain Language Summary: Climate change is intensifying the hydrologic cycle, resulting in an increase in floods and droughts. These changes increase the complexity of water resource management that must balance between releasing water to reduce flood risk and storing water for long periods without precipitation. Using updated climate model projections, we show that the amount of precipitation during events will become larger combined with longer dry periods where the daily evaporative demand exceeds precipitation for much of the Earth's surface. Additionally, for the late 21st century, a large portion of the years will be hydrologically intense in major river basins, resulting in conditions that deviate from those for which infrastructure and management policies were developed. Key Points: Precipitation events are projected to become larger and the duration between these events will be longerHeavily managed river basins in the northern and midlatitudes will experience considerable hydrological intensificationWater infrastructure and management will likely be challenged to balance flood protection and water supply among competing water uses [ABSTRACT FROM AUTHOR]

Planning under deep uncertainty, when probabilistic characterizations of the future are unknown, is a major challenge in water resources management. Many planning frameworks advocate for "scenario‐neutral" analyses in which alternative policies are evaluated over plausible future scenarios with no assessment of their likelihoods. Instead, these frameworks use sensitivity analysis to discover which uncertain factors have the greatest influence on performance. This knowledge can be used to design monitoring programs and adaptive policies that respond to changes in the critical uncertainties. However, scenario‐neutral analyses make implicit assumptions about the range and independence of the uncertain factors that may not be consistent with the coupled human‐hydrologic processes influencing the system. These assumptions could influence which factors are found to be most important and which policies are most robust, belying their neutrality; assuming uniformity and independence could have decision‐relevant implications. This study illustrates these implications using a multistakeholder planning problem within the Colorado River Basin, where hundreds of rights holders vie for the river's limited water under the law of prior appropriation. Variance‐based sensitivity analyses are performed to assess users' vulnerabilities to changing hydrologic conditions using four experimental designs: (1) scenario‐neutral samples of hydrologic factors, centered on recent historical conditions, (2) scenarios informed by climate projections, (3) scenarios informed by paleohydrologic reconstructions, and (4) scenario‐neutral samples of hydrologic factors spanning all previous experimental designs. Differences in sensitivities and user robustness rankings across the experiments illustrate the challenges of inferring the most consequential drivers of vulnerabilities to design effective monitoring programs and robust management policies. Plain Language Summary: How we should best manage our water resources depends on future water supply and demand, both of which are changing in uncertain ways as a consequence of climate change, population growth, and sectoral change. This makes it challenging to decide between alternative management plans that may be most favorable under different conditions. Given this uncertainty, many planning frameworks advocate for implementing "robust" management plans that perform reasonably well over a wide range of conditions. These plans can then be modified adaptively to cater to particular climate and socioeconomic conditions as our uncertainty about the future is reduced. Unfortunately, we find that the determination of which plan is most robust, and what conditions should trigger adaptation, is an additional challenge. In assessing the vulnerabilities of hundreds of water users in the Upper Colorado River Basin to different possible drought conditions, we find different users to be robust depending on which scenarios are considered. The sensitivities of these users' water shortages to different climate conditions also depend on which scenarios are considered. Since we do not know which scenarios are most plausible, we recommend that climate vulnerability assessments consider multiple sets of scenarios when evaluating alternative water management plans and designing monitoring programs. Key Points: Alternative experimental designs for climate vulnerability assessments lead to different inferences about important factors to monitorThese differences have implications for our ability to detect failure conditions and to rank user robustnessInconsistencies in robustness ranks across experimental designs increase with more conservative performance criteria [ABSTRACT FROM AUTHOR]