Growing impact of wildfire on western US water supply

National Academy of Sciences (NAS) | February 22nd, 2022

Streamflow often increases after fire, but the persistence of this effect and its importance to present and future regional water resources are unclear. This paper addres

Streamflow often increases after fire, but the persistence of this effect and its importance to present and future regional water resources are unclear. This paper addresses these knowledge gaps for the western United States (WUS), where annual forest fire area increased by more than 1,100% during 1984 to 2020. Among 72 forested basins across the WUS that burned between 1984 and 2019, the multibasin mean streamflow was significantly elevated by 0.19 SDs (P < 0.01) for an average of 6 water years postfire, compared to the range of results expected from climate alone. Significance is assessed by comparing prefire and postfire streamflow responses to climate and also to streamflow among 107 control basins that experienced little to no wildfire during the study period. The streamflow response scales with fire extent: among the 29 basins where >20% of forest area burned in a year, streamflow over the first 6 water years postfire increased by a multibasin average of 0.38 SDs, or 30%. Postfire streamflow increases were significant in all four seasons. Historical fire–climate relationships combined with climate model projections suggest that 2021 to 2050 will see repeated years when climate is more fire-conducive than in 2020, the year currently holding the modern record for WUS forest area burned. These findings center on relatively small, minimally managed basins, but our results suggest that burned areas will grow enough over the next 3 decades to enhance streamflow at regional scales. Wildfire is an emerging driver of runoff change that will increasingly alter climate impacts on water supplies and runoff-related risks.

Guide for Developing Onsite Water Systems to Support Regional Water Resilience

Pacific Institute | January 26th, 2023

Across the United States, urban communities face growing water challenges, from water scarcity to flooding, pollution, aging water infrastructure, and more. These challen

Across the United States, urban communities face growing water challenges, from water scarcity to flooding, pollution, aging water infrastructure, and more. These challenges present risks, but also an opportunity to rethink how we manage water, including adopting circular approaches in new buildings that reduce their water footprint and improve urban water resilience. Onsite water systems, for example, collect, treat, and reuse water from onsite sources, including wastewater, rainwater, and stormwater, for non-potable water uses like toilet flushing, outdoor irrigation, and cooling. Onsite water systems have the potential to provide multiple benefits for a site, water and wastewater systems, ecosystems, and communities. They can, for example, help companies mitigate water- related risks, like water shortages that threaten to disrupt business operations, and support corporate water stewardship goals. For communities, onsite water systems can enhance water supply reliability, improve water quality, reduce localized flooding, and increase urban green space. The realization and magnitude of benefits will vary with the type of system, scale of adoption, and other context-specific factors. This guide helps site developers consider how onsite water systems can be planned, designed, and operated to provide multiple benefits, and contribute to planning and designing onsite water systems that advance water resilience, support equity, support the environment, and protect public health at the site, water system, and community scales. For each of these outcomes, the guide provides sample questions to consider, stakeholders to engage, resources to examine, and analyses to perform.

High-elevation snowpack loss during the 2021 Pacific Northwest heat dome amplified by successive spring heatwaves

Nature Portfolio (Springer Nature) | December 13th, 2023

High‐resolution surface water dynamics in Earth’s small and medium‐sized reservoirs

Nature Portfolio (Springer Nature) | August 12th, 2022

Small and medium‐sized reservoirs play an important role in water systems that need to cope with climate variability and various other man‐made and natural challenges

Small and medium‐sized reservoirs play an important role in water systems that need to cope with climate variability and various other man‐made and natural challenges. Although reservoirs and dams are criticized for their negative social and environmental impacts by reducing natural flow variability and obstructing river connections, they are also recognized as important for social and economic development and climate change adaptation. Multiple studies map large dams and analyze the dynamics of water stored in the reservoirs behind these dams, but very few studies focus on small and medium‐sized reservoirs on a global scale. In this research, we use multi‐annual multi‐sensor satellite data, combined with cloud analytics, to monitor the state of small (10–100 ha) to medium‐ sized (> 100 ha, excluding 479 large ones) artificial water reservoirs globally for the first time. These reservoirs are of crucial importance to the well‐being of many societies, but regular monitoring records of their water dynamics are mostly missing. We combine the results of multiple studies to identify 71,208 small to medium‐sized reservoirs, followed by reconstructing surface water area changes from satellite data using a novel method introduced in this study. The dataset is validated using 768 daily in‐situ water level and storage measurements (r2 > 0.7 for 67% of the reservoirs used for the validation) demonstrating that the surface water area dynamics can be used as a proxy for water storage dynamics in many cases. Our analysis shows that for small reservoirs, the inter‐annual and intra‐annual variability is much higher than for medium‐sized reservoirs worldwide. This implies that the communities reliant on small reservoirs are more vulnerable to climate extremes, both short‐term (within seasons) and longer‐term (across seasons). Our findings show that the long‐term inter‐annual and intra‐annual changes in these reservoirs are not equally distributed geographically. Through several cases, we demonstrate that this technology can help monitor water scarcity conditions and emerging food insecurity, and facilitate transboundary cooperation. It has the potential to provide operational information on conditions in ungauged or upstream riparian countries that do not share such data with neighboring countries. This may help to create a more level playing field in water resource information globally.

Hot Drought of Summer 2023 in Southwestern North America

American Geophysical Union (AGU) | September 17th, 2025

Hot droughts, or compound drought and heatwaves, have a significant impact on arid regions in southwestern North America (SWNA). In the summer of 2023, SWNA experienced u

Hot droughts, or compound drought and heatwaves, have a significant impact on arid regions in southwestern North America (SWNA). In the summer of 2023, SWNA experienced unusually intense hot droughts during both the daytime and nighttime, with their severity amplified three to five times above values during the prior four decades. Over this period, a significant increase was found in the coupling between nighttime and daytime conditions at local scales and across different regions of the SWNA. The hot drought was due to a suppressed North American monsoon (NAM) in response to synoptic-scale subsidence and moisture divergence. Nevertheless, we identified a remote connection between soil moisture in upwind areas and hot drought conditions in downwind regions across the US-Mexico border. Our findings indicate that hot droughts need to be analyzed over complete diurnal cycles and over regions that are connected through atmospheric pathways to improve their prediction, response, and mitigation.

How Native Americans will Shape the Future of Water in the West

New Yorker | January 27th, 2023

As a child, Stephen Lewis heard stories about a river that, for the most part, no longer flowed. “How I grew up was that it was a theft, that it was stolen from us,”

As a child, Stephen Lewis heard stories about a river that, for the most part, no longer flowed. “How I grew up was that it was a theft, that it was stolen from us,” he told me late last year. “There was what we used to call the Mighty Gila River, and now it was just pretty much dry. There was no water.” Lewis is the governor of the Gila River Indian Community (gric), a group that has occupied land south of Phoenix for centuries. When I met him, in the dining room of the Whirlwind Golf Club, which the tribe owns, Lewis had recently returned from Santa Fe. There, he’d attended a celebration marking the centennial of the Colorado River Compact, an agreement that continues to shape water politics in the Southwest. In Santa Fe, Lewis took note of a black-and-white photograph of the compact’s signers—white men in dark jackets, gathered around a wooden desk.

How to address agriculture’s water woes

Nature Portfolio (Springer Nature) | June 19th, 2024

Human alteration of global surface water storage variability

Nature Portfolio (Springer Nature) | March 3rd, 2021

Knowing the extent of human influence on the global hydrological cycle is essential for the sustainability of freshwater resources on Earth. However, a lack of water leve

Knowing the extent of human influence on the global hydrological cycle is essential for the sustainability of freshwater resources on Earth. However, a lack of water level observations for the world’s ponds, lakes and reservoirs has limited the quantification of human-managed (reservoir) changes in surface water storage compared to its natural variability. The global storage variability in surface water bodies and the extent to which it is altered by humans therefore remain unknown. Here we show that 57 per cent of the Earth’s seasonal surface water storage variability occurs in human-managed reservoirs. Using measurements from NASA’s ICESat-2 satellite laser altimeter, which was launched in late 2018, we assemble an extensive global water level dataset that quantifies water level variability for 227,386 water bodies from October 2018 to July 2020. We find that seasonal variability in human-managed reservoirs averages 0.86 metres, whereas natural water bodies vary by only 0.22 metres. Natural variability in surface water storage is greatest in tropical basins, whereas human-managed variability is greatest in the Middle East, southern Africa and the western USA. Strong regional patterns are also found, with human influence driving 67 per cent of surface water storage variability south of 45 degrees north and nearly 100 per cent in certain arid and semi-arid regions. As economic development, population growth and climate change continue to pressure global water resources, our approach provides a useful baseline from which ICESat-2 and future satellite missions will be able to track human modifications to the global hydrologic cycle.

Human-Induced Changes in the Hydrology of the Western United States

American Association for the Advancement of Science (AAAS) | February 22nd, 2008

Observations have shown that the hydrological cycle of the western United States changed significantly over the last half of the 20th century. We present a regi

Observations have shown that the hydrological cycle of the western United States changed significantly over the last half of the 20th century. We present a regional, multivariable climate change detection and attribution study, using a high-resolution hydrologic model forced by global climate models, focusing on the changes that have already affected this primarily arid region with a large and growing population. The results show that up to 60% of the climate-related trends of river flow, winter air temperature, and snow pack between 1950 and 1999 are human-induced. These results are robust to perturbation of study variates and methods. They portend, in conjunction with previous work, a coming crisis in water supply for the western United States.

Hydroclimate Report Water Year 2015

California Department of Water Resources (DWR) | December 23rd, 2016

Water year 2015 added a fourth year to the ongoing drought in California, with observations indicative of a changing climate, including record warmth. The Water year ende

Water year 2015 added a fourth year to the ongoing drought in California, with observations indicative of a changing climate, including record warmth. The Water year ended with record high temperatures, and preceded a period of historically low precipitation that started in 2012. April snowpack measurements in 2014 tied the historic record low of 1977. Expectations of a developing El Niño event in the eastern tropical Pacific fueled notions that water year 2015 would be better. However, during the first two months of the water year, warm temperatures persisted and precipitation continued to fall short of expectations.  The developing El Niño event stalled as California headed into the heart of its wet season. In 2014, the snowpack level was 25% of its average on April 1. That mark was shattered on April 1, 2015 when snowpack amounted to a meager 5% of average. Satellite-imagery compares the Sierra Nevada snowpack near the end of March 2015 to the average conditions in water year 2011. This extreme low in snowpack exceeds end-of-century climate projections. When accompanied by the record warm temperatures experienced in the 2015 water year, there is conversation of California having shifted to a new climate “normal”.