Abstract
As drought occurs in a region it can have cascading effects through the water cycle. In this study, we explore the temporal co-evolution of various components of the hydrologic cycle in California from 2002 to 2018. We combine information from the Gravity Recovery and Climate Experiment (GRACE) satellites, the North American Land Data Assimilation System (NLDAS) suite of models, and the California Department of Water Resources (DWR) reservoir levels to analyze dynamics of Total Water Storage (TWS), soil moisture, snow pack, large reservoir storage, and ultimately, groundwater. For TWS, a trend of −2 cm/yr is observed during the entire time period of our analysis; however, this rate increases to about −5 cm/yr during drought periods (2006−2010 and 2012−2016). Results indicate that the majority of the loss in TWS is caused by groundwater depletion. Using proper error accounting, we are able to identify the start, the peak, and the ending of the drought periods for each individual water state variable in the study domain. We show that snow and soil moisture are impacted earlier and recover faster than surface water and groundwater. The annual and year-to-year dynamics shown in our results portray a clear cascading effect of the hydrologic cycle on the scale of 8−16 months.
Highlights
In recent decades, the demands of fresh water for urban, agricultural, and environmental uses have exceeded the natural renewable supply in many regions of the world, especially for arid and semi-arid regions such as California [1,2]
These results indicate that the majority of the loss in Total Water Storage (TWS) is caused by groundwater depletion
In Figure 4E−G, we show that groundwater makes up 60%−90% of the signal seen in TWS loss
Summary
The demands of fresh water for urban, agricultural, and environmental uses have exceeded the natural renewable supply in many regions of the world, especially for arid and semi-arid regions such as California [1,2] To date, this gap between the available surface water supply and the growing water demand has caused significant stresses on fresh water systems globally. Various aspects of the hydrologic cycle, such as snow pack and soil moisture, have been impacted by increasing temperatures and more variable precipitation This overall shock to the water cycle can be seen in both observations and model simulations of total water storage for many regions of the world [7,8,9,10,11,12]
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