The West Wide Drought Tracker: Drought Monitoring at Fine Spatial Scales

American Meteorological Society (AMS) | September 1st, 2017

 The western United States has seen increases in population and water use over the past century. Total water use has remained relatively unchanged over the past several

 The western United States has seen increases in population and water use over the past century. Total water use has remained relatively unchanged over the past several decades due to water conservation efforts. However, water scarcity has become more acute across much of this semiarid region during recent decades due to long-term declines in water storage juxtaposed with the region’s notable hydroclimatic variability. Observed declines in mountain snowpack and increases in atmospheric demands tied to long-term warming trends have further exacerbated water scarcity and increased the importance of monitoring efforts given the array of social, economic, and ecosystem sectors dependent upon the already stressed water supply. The recent severe drought in California and protracted drought across much of the southwestern United States over the past couple decades have prompted demand for accessible drought decision-making information at appropriate spatial scales across the western United States. 

Third Supplement To State Water Resources Board Bulletin No. 11, San Joaquin County Investigation, Basic Data, Calaveras Unit 1956-57

California Department of Water Resources (DWR) | January 21st, 1958

Thirstwaves: Prolonged Periods of Agricultural Exposure to Extreme Atmospheric Evaporative Demand for Water

American Geophysical Union (AGU) | March 20th, 2025

Global atmospheric evaporative demand has increased, impacting agricultural productivity and water use. Traditionally, trend assessments have been limited to total evapor

Global atmospheric evaporative demand has increased, impacting agricultural productivity and water use. Traditionally, trend assessments have been limited to total evaporative demand, overlooking shifts in daily extremes, which are meaningful for agrohydrological outcomes yet largely unknown. Here, using a fully physical metric of evaporative demand, that is, standardized short crop reference evapotranspiration, we introduce the concept of thirstwaves—prolonged periods of extremely high evaporative demand—and analyze their characteristics during 1981–2021 growing seasons for the conterminous US. Findings show that long-term mean spatial patterns demonstrated by thirstwave characteristics do not follow that of total or mean evaporative demand. Weighted for cropland area harvested, thirstwave intensity, duration, and frequency have increased by 0.06 mm d−1 decade−1, 0.10 days decade−1, and 0.39 events decade−1, respectively during 1981–2021. Statistically significant trends appear across 17%, 7%, and 23% of cropland area for intensity, frequency, and duration. Not only have thirstwaves increased in severity, but the likelihood of no thirstwaves occurring during the growing season has significantly decreased. Our work proposes a novel metric to describe periods of extremely elevated evaporative demand and presents a systematic analysis of such conditions historically for US croplands.

Thousands of domestic and public supply wells face failure despite groundwater sustainability reform in California’s Central Valley

Nature Portfolio (Springer Nature) | September 8th, 2023

Total Water Management Study for the Central Valley Basin, California, Central Valley Project Intermittent Surface Water Supply, Working Document No. 6

U.S. Bureau of Reclamation (USBR) | April 1st, 1975

Total Water Management Study for the Central Valley Basin, California, Central Valley Project Water Yield Risk Working Document No. 5

U.S. Bureau of Reclamation (USBR) | February 1st, 1975

Total Water Management Study for the Central Valley Basin, California, Interim Water Supply Working Document No. 9

U.S. Bureau of Reclamation (USBR) | March 1st, 1976

Toward a Resilient Global Society: Air, Sea Level, Earthquakes, and Weather

American Geophysical Union (AGU) | April 30th, 2019

Society's progress along the four corners of prepare, adsorb, respond and adapt resilience square is uneven, in spite of our understanding of the foundational science and

Society's progress along the four corners of prepare, adsorb, respond and adapt resilience square is uneven, in spite of our understanding of the foundational science and a growing sense that urgent action is needed. The resilience vignettes describe the meaning and impact of current and near‐term change in four major domains: human health impacts from air pollution, coastal inundation from sea‐level rise, damaging earthquakes in populated areas, and impacts from extreme precipitation. Given our understanding of the scientific principles, societal action, from preparation to adaption, will be critical in minimizing the negative impacts of today's changes. The unprecedented rates of change in today's Earth system argue for urgent action in support of a resilient global society.

Tracking California’s striking water storage gains attributed to intensive atmospheric rivers

Journal of Hydrology (Elsevier) | February 5th, 2025

California is highly vulnerable to extreme precipitation events due to the dense landfall of atmospheric rivers (ARs) during the winter months, often resulting in catastr

California is highly vulnerable to extreme precipitation events due to the dense landfall of atmospheric rivers (ARs) during the winter months, often resulting in catastrophic consequences such as widespread floods, mudslides, and landslides. This study focuses on the recovery of daily variations in AR-driven terrestrial water storage (TWS), which produces geodetically detectable ground subsidence. We invert GNSS vertical positions to obtain daily estimates of equivalent water height (EWH) through a variational Bayesian principal component analysis (vbPCA) based inversion scheme and track significant water gains during record-setting winter months in four water years (WYs) 2011, 2017, 2019, and 2023. These precipitation extremes have resulted in a substantial short-term increase in water storage, as evidenced by the multi-source EWH datasets (GNSS, GRACE, and NLDAS). Notably, WY 2023 experienced the highest snowfall due to the landfalls of high-density, high-category ARs, while WY 2017 recorded the highest precipitation totals, driven by the most frequent occurrence of hazardous ARs. Our findings further highlight that GNSS can accurately detect exceptionally wet hydrological events on short time scales, benefiting from an improved signal-to-noise ratio due to substantial increase in water storage. The results also indicate that while these extreme water years can help alleviate surface subsidence in the Central Valley caused by groundwater overexploitation, it is insufficient to alter California’s heavy reliance on groundwater for its intensive agricultural activities. Our findings demonstrate that GNSS is successful in tracking prodigious water increases from short-term precipitation extremes that are weaker than powerful hurricanes, illuminating the prospect of GNSS in supporting water management and flood preparedness.

Tracking Where Water Goes in a Changing Sacramento–San Joaquin Delta Technical Appendix: Methods and Detailed Results for 1980–2021

Public Policy Institute of California (PPIC) | May 26th, 2022

Our goal is to provide water policymakers, managers, and regulators with information that will be helpful in managing the Delta and its watershed for multiple objectives

Our goal is to provide water policymakers, managers, and regulators with information that will be helpful in managing the Delta and its watershed for multiple objectives as warming conditions increase water demand, reduce snowpack, and make it harder to balance these objectives. An accompanying policy brief summarizes the findings presented here and highlights the major policy recommendations. This appendix provides details and evidence to support those recommendations and is intended for both a technical and policy audience. In the following sections we first review our approach for categorizing water flows in the watershed, and we review the caveats and limitations of the analysis. We next present key results and discuss several important watershed trends. We then review the management challenges of changing conditions in the Delta in wet and dry years through the lens of detailed water accounting. We conclude with implications for policy and management, including recommendations to improve watershed accounting and adapt the regulatory and management framework to the changing conditions in the watershed. All data assembled for this study, along with the sources and methods used, are detailed in the accompanying PPIC Delta Water Accounting spreadsheets.