The North American Land Data Assimilation System Phase 2 (NLDAS-2) is run daily by NOAA's NCEP Central Operations to model soil temperature, soil moisture, surface fluxes, snow pack, and other land variables in near-real-time. The figures on this page show soil temperatures at 10-40 cm (3.94-15.75 inches) below ground level from NLDAS-2, as a proxy method for monitoring Brood X cicada emergence in Maryland. Previous studies show that 17-year periodical cicadas such as Brood X will, on average, emerge when the soil 8 inches below the ground reaches 64.5 F.
NLDAS-2 generates these fields by running several land-surface models (LSMs) that are forced with high-quality surface observations, including a precipitation gauge analysis. Hourly, monthly, and monthly climatology datasets going back to Jan 1979 are available from the NASA GES DISC.
DISCLAIMER: These figures are produced only for local interest, and do not represent any official cicada emergence monitoring or forecast. The data on these figures are not observations or measurements; the data is from a land-surface model simulation using best-available input data.
Figure 1 shows the latest available NLDAS-2 Noah LSM soil temperatures for the 10-40cm below ground layer centered over Goddard Space Flight Center (GSFC) in Greenbelt, Maryland. The boxes in the image represent the average temperatures over the 1/8th-degree by 1/8th-degree spatial grid of the NLDAS-2 dataset, with the grey circle with a purple outline indicating the approximate location of GSFC.
Figure 1: NLDAS-2 Noah LSM 10-40cm soil temperature [F] map centered over GSFC in Maryland.
Figure 2 shows the past 30-day time series of the NLDAS-2 Noah LSM soil temperature for the 10-40cm below ground layer for the grid box at and on the northeast side of GSFC (39.0 North and -76.8 West). The grid box on the northeast side of the circle shown in Figure 1 is shown for the time series due to the heavily-wooded area on the northeast side of GSFC.
Figure 2: NLDAS-2 Noah LSM 10-40cm soil temperature [F] time series at/near GSFC in Maryland (at the point 39.0 North and -76.8 West).
Figure 3 shows time series (extended to July 1st) of the NLDAS-2 Noah LSM soil temperatures for same soil layer and location (at GSFC). Also shown on Figure 3 are the time series of the temperatures for the Brood X cicada years of 2004 and 1987, as well as the climatological average temperatures (over 1979 to 2020, inclusive). Based on reports from 2004 for Brood X emergence in mid-May in this region, it's possible that the average soil temperatures over the entire 10-40cm layer (from ~4 to 15.75 inches below ground) will lag by about a week behind emergence.
Figure 3: NLDAS-2 Noah LSM 10-40cm soil temperature [F] time series at/near GSFC in Maryland
for the Brood X cicada years of 2021, 2004, 1987, as well as the climatological average.
for the Brood X cicada years of 2021, 2004, 1987, as well as the climatological average.
These figures will be updated daily (typically before 4:50pm EDT) to monitor the changing soil temperatures. The bottom right of the figures indicates when they were last updated. Please note that there is a 4-day latency of the NLDAS-2 dataset, so after the daily update, the latest available data shown on the plots will represent the temperatures as of 4 days ago.
Based on previous years, Brood X typically begins to emerge around mid-May. However, a warmer or cooler spring can move this timeline earlier or later. This Washington Post article on cicadas addresses the Brood X cicada timeline, as well as showing an emergence map and answering other questions. Cicadas can emerge earlier or later in individual locations than the average temperatures simulated by the NLDAS-2 Noah LSM on the 1/8th-degree grid.
David Mocko and Eric Kemp