Full Reservoirs and Drought
The recently released drought map from the National Oceanic and Atmospheric
Administration (NOAA) looks like another looming crisis, which is red meat for journalists.
The data made available by the U.S. Drought monitor on January 1 highlights areas categorized as “abnormally dry” or in “moderate drought.” However, a closer look at other data from the California Data Exchange Center (CDEC) presents a contrasting perspective, showing that 14 of the state’s 17 largest reservoirs are currently at or above year-to-date historical averages. Most are at 70 percent or more of their full capacity and precipitation levels are only slightly below average for this time of year.
This raises important questions about how “drought” conditions are assessed and interpreted.
Seasonal Context is Key
California’s unique climate heavily influences its water cycle. The state relies on the snowpack accumulated in the Sierra Nevada during the wetter months of January and February to sustain its water supply through the dry summer. This dependency on a sliver of the entire year underscores the importance of not drawing premature conclusions about drought status based solely on early winter conditions.
While NOAA’s drought map captures soil moisture deficits and other short-term metrics, these indicators can sometimes overshadow the broader picture. For example, CDEC’s data reveals that major reservoirs, including Shasta, Oroville, and Folsom, are holding strong at or near capacity—a direct result of last year’s extraordinary precipitation. This reservoir stability significantly mitigates the risk of immediate water shortages, which is different than a blanket determination about a potential drought.
Parsing the Precipitation Numbers
As of now, precipitation totals across California are only slightly below the historical average for this point in the water year, which began on October 1. NOAA’s map may reflect the lingering effects of a dry November, but December’s rain and snow conditions improved, with storms replenishing water supplies in many areas, including a significant jump in Shasta storage, California’s largest reservoir. The disparity between the drought map and reservoir levels underscores the need for a nuanced understanding of California’s hydrology.
Balancing Indicators: Short-Term vs. Long-Term
NOAA’s drought map integrates data such as soil moisture, streamflow, and precipitation deficits, which are important for understanding potential short-term agricultural and ecological stress. However, this approach may not fully account for the resilience provided by above average reservoir levels and the potential for significant snowpack accumulation in the months ahead.
This year’s water outlook, like all years, will depend mostly on the intensity and duration of storms we receive in January and February, historically the state’s wettest months. California’s water planners are watching these months closely, as they determine not only the snowpack but also the runoff that feeds reservoirs in the spring.
A Hopeful Outlook
While NOAA’s drought map may raise alarms, it’s crucial to compare these findings within the state’s overall water conditions. The strong reservoir levels reported by CDEC offer reassurance that California is better positioned to weather potential dry spells. With most of January and February—the peak of California’s snow season—still ahead, there is every reason to remain optimistic about the state’s water future.
As we close out 2024 and head into the heart of the water year, Californians can take comfort in knowing that the critical months for snow and rain are still ahead. Historical patterns suggest that the state’s hydrology can shift dramatically in just a few weeks, providing the necessary precipitation to maintain a stable water supply.
While it’s important to approach water supply planning from a conservative perspective, decisions should be made using all the available data to avoid creating artificial water shortages when it’s unnecessary.