Abstract
The study explores the potential changes in water year types and hydrological droughts as well as runoff, based on which the former two metrics are calculated in the Central Valley of California, United States, in the 21st century. The latest operative projections from four representative climate models under two greenhouse-gas emission scenarios are employed for this purpose. The study shows that the temporal distribution of annual runoff is expected to change in terms of shifting more volume to the wet season (October–March) from the snowmelt season (April–July). Increases in wet season runoff volume are more noticeable under the higher (versus lower) emission scenario, while decreases in snowmelt season runoff are generally more significant under the lower (versus higher) emission scenario. In comparison, changes in the water year types are more influenced by climate models rather than emission scenarios. When comparing two regions in the Central Valley, the rain-dominated Sacramento River region is projected to experience more wet years and less critical years than the snow-dominated San Joaquin River region due to their hydroclimatic and geographic differences. Hydrological droughts in the snowmelt season and wet season mostly exhibit upward and downward trends, respectively. However, the uncertainty in the direction of the trend on annual and multi-year scales tends to be climate-model dependent. Overall, this study highlights non-stationarity and long-term uncertainty in these study metrics. They need to be considered when developing adaptive water resources management strategies, some of which are discussed in the study.
Highlights
There is growing evidence that global warming is changing the water cycle in terms of altering the spatial and temporal distributions of water availability worldwide
CMIP3 projections in the [21] study) that are selected for planning studies in California (CCCA4); and, (2) the current study uses the observed water year types as the historical baseline in comparison; and, (3) the current study examines the changes in a 80-year period, which provides more samples for each of five categories of water year types
This study highlights the non-stationarity and long-term uncertainty in key variables typically applied in guiding water resources planning and management in the State of California, United States
Summary
There is growing evidence that global warming is changing the water cycle in terms of altering the spatial and temporal distributions of water availability worldwide. The changes are projected to intensify through the end of this century [10,11,12,13,14,15]. These changes have profound impacts on water resources management, in water-limited arid or semi-arid environments, including the State of California, United States (U.S.). As a globally important economy, California is the most populous State and one of the most productive agriculture areas in the United States [16]. The State has built a vast and complex water storage and transfer system to redistribute water from the wetter northern half of the State to the drier southern half, which has a higher population and water demand and, from the wet season to the dry season, when the demand is the highest but precipitation is minimal, to support its population/agriculture and sustain its economy
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