Home » Supplemental Figures for the December 2011 La Niña Drought Tracker

Supplemental Figures for the December 2011 La Niña Drought Tracker

Supplemental Figure 1. La Niña events were weak during seven winters since 1950. La Niña events, according to the National Oceanic and Atmospheric Administration (NOAA), occur when the sea surface temperature (SST) anomaly in the tropical Pacific Ocean (in the Niño 3.4 region) is at least 0.5 degrees Celsius below average. Weak La Niña events occur when the SST anomaly is between 0.5 and 1.0 degrees C below average, and is classified here as weak when this range is breached for at least one three-month season. Precipitation during of all those events for the November–March period was generally less than 90 percent of the 1971–2000 average in Arizona, which many parts of New Mexico received slightly above-average precipitation. The years include 1956–57, 1962–63, 1967–68, 1971–72, 1974–75, 1995–96, and 2000–01. The analysis is based on monthly PRISM data and Westmap generated the map.

 

Supplemental Figure 2. Supplemental Figure 2. La Niña events reached moderate strength during eight winters since 1950. Moderate La Niña events occur when the SST anomaly is between-1.0 and -1.5 degrees C in the Niño 3.4 region, and is classified here as moderate when this range is breached for at least one three-month season. Precipitation during of all those events for the November –March period was generally less than 75 percent of the 1971–2000 average. The years include 1950–51, 1954–55, 1964–65, 1970–71, 1984–85, 1998–89, 2007–08, 2010–11. The analysis is based on monthly PRISM data and Westmap generated the map.

 

Supplemental Figure 3. La Niña events were classified as strong during six winters since 1950. Strong La Niñas occur when the SST anomaly is less than or equal to -1.5 degrees C below average in the Niño 3.4 region, and is classified here as strong when this threshold is breached for at least one-three month season. Precipitation during of all those events for the November –March period was generally less than 75 percent of the 1971–2000 average, with many areas receiving less than 50 percent of average. The years include 1949–50, 1955–56, 1973–74, 1975–76, 1988–89, 1999–00. The analysis is based on monthly PRISM data and Westmap generated the map.

 

Supplemental Figure 4. Probabilistic El–Niño Southern Oscillation (ENSO) forecasts suggest a high likelihood the current La Niña will persist into spring 2012. The event is currently weak but could intensify and reach a moderate strength. Figure source: International Research Institute for Climate and Society.

 

Supplemental Figure 5. During the 20 winters since 1950 in which La Niña was present, December precipitation in southern Arizona and New Mexico generally was slightly below the 1971–2000 average, while many northern areas received above-average rain and snow. The analysis is based on monthly PRISM data and WestMap generated by map.

 

Supplemental Figure 6. During the 20 winters since 1950 in which La Niña was present, January precipitation was generally below average, with some southern regions receiving less than 50 percent of the 1971–2000 average. The analysis is based on monthly PRISM data and Westmap generated the map.

 

Supplemental Figure 7. During the 20 winters since 1950 in which La Niña was present, February precipitation was generally below average, with nearly all of Arizona receiving less than 75 percent of the 1971–2000 average. The analysis is based on monthly PRISM data and Westmap generated by map.

 

Supplemental Figure 8. During the 20 winters since 1950 in which La Niña was present, March precipitation was below average in nearly all of Arizona, with some western and southern areas receiving less than 25 percent of the 1971–2000 average. Southern parts of New Mexico, however, received above-average precipitation. The analysis is based on monthly PRISM data and Westmap generated the map.

 

Supplemental Figure 9. Many basins in Arizona and New Mexico have above-average snow water equivalent (SWE). SWE is a common unit of measurement that records the amount of water contained in the snow and is measured by Snow Telemetry (SNOTEL) stations. Storms between December 1 and 4 helped boost these numbers. The Upper Colorado River Basin, however, currently has below-average SWE, while the upper Rio Grande has slightly above-average SWE. Figure source: Natural Resources Conservation Service.

 

Supplemental Figure 10. The majority of winters in which La Niña conditions were present produced streamflow in the Verde River (measured above Horseshoe Dam) that was less than the average for this period; average flows for March–May have been about 100,000 acre-feet since 1937. The graph shows the March–May streamflows during El Niño, La Niña, and neutral winters for each year,labeled on the plot,since 1951. Figure source: modified from the Colorado River Basin Forecast Center.

 

Supplemental Figure 11. The majority of the winters in which La Niña conditions were present produced streamflow in the Salt River (measured near Roosevelt Lake) that was below the 1937–2011 average of sbout 230,000 acre-feet. March–May is the period that produces the majority of the annual streamflow. The graph shows the March–May streamflows during El Niño, La Niña, and neutral winters for each year, labeled on the plot, since 1951. Figure source: modified from the Colorado River Basin Forecast Center.

 

Supplemental Figure 12. About two-thirds of the Colorado River’s spring streamflows measured at Lake Powell’s Glen Canyon Dam fall below the historic average of 8 million acre-feet during La Niña events. But, some of the highest recorded flows have occurred during La Niña events such as the streamflow in 2011. The graph shows the April–June streamflows during El Niño, La Niña, and neutral winters for each year, labeled on the plot, since 1951. Figure source: modified from the Colorado River Basin Forecast Center.

 

Supplemental Figure 13. The precipitation outlook produced by the NOAA-Climate Prediction Center (CPC) calls for slightly increased chances for above-average precipitation in December. Chances for drier-than-average conditions increase in subsequent months, reaching as high as 50–60 percent in southern parts of the Southwest. The expectation that La Niña will persist heavily influences this outlook. Figure source: NOAA-CPC

 

Supplemental Figure 14. Between 60 and 80 percent of the La Niña events during the 1950–2010 period contributed to precipitation totals between 0.4 (10 mm) and 1.2 inches (30 mm) below the December–February average in many parts of Arizona and New Mexico. This suggests that conditions likely will be dry in the coming months, and these statistics feed the below-average precipitation outlooks and the forecasts for expanding or persisting drought issued by NOAA-CPC. The image on the right displays the percent of La Niña events in which the anomalies in the left image occurred, (10 mm equals about 0.4 in.). The year of the La Niña events are indicated at the bottom of the figure.

 

Supplemental Figure 15. Based in large part on La Niña’s effect on decreasing precipitation in Arizona and New Mexico, the December 1 Seasonal Drought Outlook calls from persisting, intensifying drought conditions in many parts of the region. Figure source: NOAA-Climate Prediction Center.

Supplemental Figure 16. Given the intense and widespread drought in the Southwest, it is unlikely that precipitation during the November–March period will be sufficient to end drought. Chances that drought will end by March are less than 10 percent for most of New Mexico and less than 15 percent for southern Arizona. This analysis uses the historical precipitation record to calculate the odds that current drought conditions (defined by the Palmer Drought Severity Index) will end in each climate division. Figure source: NOAA-National Climatic Data Center. Supplemental Figure 17 indicates the percent of average precipitation needed needed to end a drought.

Supplemental Figure 17. Given the intense and widespread drought in the Southwest, it is unlikely that precipitation during the November–March period will be sufficient to end drought. For most of New Mexico, precipitation needs to exceed 200 percent of the average for this period to end drought in November (drought conditions did not substantially change between the release of this figure in November and the publication of this issue of the La Niña Drought Tracker). Southern Arizona needs more than 175 percent of average rainfall to end drought. Supplemental Figure 16 indicates the likelihood that regions will receive the quantity of precipitation needed to end a drought.