Multi-Year Forecasts of Colorado River Water Supply

Perspective

Ocean precursors suggest the current drought persists until 2023 water years at least (red lines in Figure 1). Sea surface temperature warmings in the North Pacific and the tropical Atlantic are the preferable condition for natural streamflow reduction of the Colorado River in the 2023 water year (Figure 3). These results imply that the Colorado River Basin is under a prolonged dry period. However, these temperature warmings turn to be weakened for the latest forecast, expecting a slight recovery from drought in the 2024 water year. The next forecast update for the 2025 water year would provide a better perspective on whether the current multi-year drought has worsened or not. (updated Jul 22, 2022)

Figure 1:Forecasts of ocean-induced Colorado River water supply. Blue and red lines are the observed water supply provided by the Bureau of Reclamation and the forecasts based on ocean precursors. Thin and thick lines correspond to annual and three-year averages based on the water year, respectively. We obtain the forecast by averaging three forecasted water supply products based on the three ocean datasets (see Figure 2 below).

The next forecast will be in the 2023 Summer.

Technical Contents

Figure 2:Timeseries show the Colorado River water supply (blue) and its forecasts (orange). The Colorado River water supply corresponds to the water year natural streamflows at Lees Ferry, AZ (Bureau of Reclamation). Forecasts rely on two ocean precursors: sea surface temperature anomalies in the North Pacific 29 months ago and the southern tropical Atlantic 44 months ago. We calculated the forecasts based on three different sources of the observed sea surface temperature datasets: COBS SST, OI SST, and ERSSTv5. These forecasts indicate the ocean-induced multi-year drought threats (Chikamoto et al., 2020), explaining about 25% of the total variance. The short atmospheric drought is unpredictable in our model. Please check the seasonal predictions if you are interested in a medium-range forecast.

Ocean Precursors

1964 1967 1977 1991 2001 2002 2003 2020 2021 2022 2023 2024

Figure 3: Our multi-year forecasts of the Colorado River water supply result in the combination of two ocean precursors. A chance for the severe natural streamflow reduction of the Colorado River becomes higher during the warmer sea surface temperatures than usual in the southern tropical Atlantic 44 months ago and the North Pacific 29 months ago. In history, our ocean drought indicator (i.e., the orange lines above) detected eight events of natural streamflow reduction: 1964, 1967, 1977, 1991, 2001, 2002, 2003, and 2020 water years. The graph below shows sea surface temperature anomalies at 44 (left) and 29 months ago (right) for the specific year (upper) and the all years composite (lower panels). You can check these ocean precursors by selecting the year from the toggle. Ocean precursors for the current and the next water years are also available.