Summary and Conclusions

Key Conditions and Trends:

This report presented 22 indicators across a spectrum of topics including land use, land cover, water supply, water demand, development, planning, and demographics, which have important implications for the water future of the Colorado River Basin and Adjacent Areas Served (CRBAAS). First, diminishing water supplies provide the backdrop for all the other indicators. Streamflow in the Upper Colorado has declined by roughly 20% over the last century and streamflow reductions have intensified in the last 23 years due to the Millennium Drought. That trend is predicted to continue as the climate warms, despite potential increases in precipitation (Williams et al. 2022 Citation; Milly and Dunne 2020 Citation; Overpeck and Udall 2020 Citation; Hoerling et al. 2019 Citation; Udall and Overpeck 2017 Citation; Woodhouse et al. 2016 Citation). Forest loss due to warming temperatures, drought, wildfire, development, and other disturbances further endangers future water supplies in the CRBAAS Definition (Williams, Cook, and Smerdon 2022 Citation; Goeking and Tarboton 2020 Citation; Rodman et al. 2020 Citation; McDowell et al. 2016 Citation).

Against this backdrop of declining streamflows, people continue to flock to CRBAAS communities. The population of the CRBAAS¹ grew from 39.8 million in 2015 to 43.5 million in 2020, and growth in CRBAAS counties is expected to reach 47.6 million by 2030, assuming average growth (shared socioeconomic pathway 2 [AF1] [RL2] [SSP2] Definition). The estimated number of households in CRBAAS counties for 2023 is 15.2 million, up 5 percent from five years ago. Meanwhile, the average household size has remained relatively stable, at 2.6 persons. The impact of population increase on water resources depends largely on the density and urban form of the associated land development. The developed area in the Basin has increased by 16.7% over the last two decades, with high-intensity development—which contains industrial or commercial and residential mixed uses—accounting for the most growth. The proportion of single-family zoning increased in 70 of the 120 CRBAAS counties. These population and development trends all pose demand-side water challenges to a sustainable water future (Brown 2019 Citation; McGrane 2016 Citation). Some positive trends regarding water demand include reduced median lot sizes across the West and drops in per capita water use from a Basin-wide average of 223 GPCD Definition in 2005 to 179 GPCD in 2015. The price of water in the Basin is close to the national average. However, 32 of the 37 communities sampled have implemented tiered water-rate structures to reduce wasteful water use, while increasing the number of users paying a price approaching the long-term marginal cost of water for utilities to supply water (Olmstead and Stavins 2009 Citation).

We have analyzed how water is integrated into communities’ comprehensive plans. While strides have been made, many of our sampled communities would benefit from additional technological and financial support, capacity, and knowledge sharing. Numerous state-level opportunities exist to incentivize or require communities to include water elements in their comprehensive plans, and they provide the resources necessary to do so.

Communities in the CRBAAS will be increasingly challenged by natural hazards or disasters such as wildfires, droughts, flooding, and heat waves. The number of extreme hydroclimatic events has doubled in the last five years, due to climate change, undermining regional economic stability (Bennett, Talsma, and Boero 2021 Citation). Extreme heat and precipitation are projected to increase and intensify within the Colorado River Basin (Bennett, Talsma, and Boero 2021 Citation). In the face of these risks, levels of social vulnerability are low in the Lower Basin and high in the Upper Basin relative to national averages. Lower vulnerability scores in the Lower Basin likely result from large urban populations vulnerable to extreme heat, as well as agricultural areas that have drought risks among the highest in the nation. Lower Basin communities also have a relatively high risk of wildfire. Front-Range communities in the Denver metroplex face an increased risk of cold waves, hail, lightning, flooding, and tornados.

The Upper Basin has higher resilience (the ability to prepare for, respond to, and recover from natural hazards), while Lower Basin communities, particularly tribal communities, have among the lowest resilience scores. Agricultural counties like Pinal, AZ, have relatively low community resilience scores coupled with high exposure to drought impacts, leading to very high annual losses compared to in other areas in the Basin.

Conclusion

Despite the positive trends in per capita water use, continuing improvements in water use efficiency will be necessary. However, such improvements may be insufficient to avoid future water shortages (Brown 2019 Citation). Rapidly growing urban areas in the Basin must arrive at creative solutions involving the agricultural sector to mitigate future water shortages (Brown 2019 Citation). How land is used has outsized impacts on water quality and availability, but land and water management remain largely siloed (Endter-Wada et al. 2022a Citation). Ample room and need exist for institutions and transboundary organizations that connect land and water policy at federal, state, and local levels and approach water security from different angles (Endter-Wada et al. 2022b Citation). The Babbitt Center and its partners will continue to monitor change in land and water use throughout the Basin.

While the indicators we have presented in this report provide a solid foundation for the overall status of the CRBAAS, they are not exhaustive. Consequently, we are developing several more indicators to release in subsequent reports. Our interactive dashboard contains data beyond those described here and curates’ other data-sets, pulling together indicators and analyses from other organizations alongside our own. Future topics for indicator development include water security; surface water supply in the Upper Basin; outdoor municipal water use; urban heat; agriculture; groundwater; wildfire; climate change; and drought. These indicators will go further in showing the condition and trends of the lands and waters in the CRBAAS.

Finally, we believe there is a major need for indicators that measure the integration of land use planning and water management in communities across the CRBAAS. Developing such indicators can pose a major challenge because they require in-depth and sustained participation, data sharing, data standardization, and coordination among administrative entities across state, county, and municipal boundaries. At the outset, this was our goal, but after communicating with several of our indicator communities, we recognized that developing indicators for individual communities to use to gauge their own progress would require significant resources. There is, however, hope, as large-scale data-sets become more available via web tools and applications that provide finer resolution data. Additionally, tools and metrics are available for motivated communities to begin tracking land and water integration, such as the Growing Water Smart Metrics developed by the Sonoran Institute. Movements toward open water data are starting to gain ground—including calls for a National Water Data Portal, which could be critical to understanding future risks and informing effective water management (Josset et al. 2019 Citation). The ongoing drought on the Colorado is already forcing cuts to water use within the Basin and will encourage communities to analyze water use and water supplies at an increasingly granular level. We invite your collaboration and suggestions for future indicators.

Integrating land use management and water resource management has never been more important in the Colorado River Basin and Adjacent Areas Served (CRBAAS). While climate change, forest loss, and wildfire continue to threaten the quantity, quality, and timing of streamflow and water supplies, population growth, development, and changes in land use will lead to shifts in water demand. Addressing the challenges that these changes to supply and demand will have on the arid West requires a holistic approach to water and land management that crosses administrative boundaries. This report is an initial offering to consider myriad different land and water indicators in the Colorado River Basin with the express intention to establish a baseline. The scale of the indicators presented is thus far broad, focusing on Basin-wide, state, county, and municipal trends.