One of the most common weather-related aphorisms many of us know is “April showers bring May flowers.” In many areas of the United States, April is traditionally a rainy month. Occasionally, when April showers go on a rampage, the unfortunate consequences of the resulting excessive rainwater, combined with water from snowmelt, saturated soil, and even delayed or slowed growth of plants, can cause severe flooding.
This April, spring weather was cool and rainy. An abnormal spell of cold weather delayed the blooming of cherry blossoms in the nation's capital (Fig. 1). In the Midwest, meanwhile, cold air from the north collided with warm, moisture-rich air flowing north from the Gulf of Mexico, resulting in extremely high rainfall totals in some areas.
Figure 1: The cherry blossoms around the Tidal Basin in Washington D.C. bloomed this year much later than they did in previous years, due to the abnormally cold April weather. Photo by Zhong Liu. (Click to view full-size.)
A particularly hard-hit area was the city of Chicago and its suburbs, where the Des Plaines River normally flows placidly through parks and forest preserves suitable for picnics and outdoor recreation. The April rains falling in the area flooded the parks and nearby suburban streets, including the location of the first McDonald’s restaurant in the downtown area of the City of Des Plaines. The original McDonald’s is now a museum, with the original Golden Arches architecture restored – and a vintage price for a hamburger (15¢) displayed (Fig. 2). However, a fish sandwich might have been more appropriate when these pictures were taken! The Des Plaines River crested at a record high level of 10.92 feet, 0.02 foot higher than the previous record, which occurred in 1986.
Figure 2. The Des Plaines River flooded low-lying areas of the City of Des Plaines, following the heavy rain event of April 18. (a) Aerial view of the downtown area. (b) Closer view of the first McDonald’s restaurant museum. (c) River Road in Des Plaines temporarily—and literally—became a river. (d) Numerous suburban streets were flooded; this is Oakton Street in Des Plaines. (Click on any image to view at full resolution.)
On April 18, 2013, more than 130 mm (~5-6 inches) of rain fell in the Chicago area in 24 hours (Fig. 3), based on the near-real-time quasi-global (50° N - 50° S) rainfall product, TRMM Multi-satellite Precipitation Analysis (TMPA-RT), developed by Dr. George Huffman at the NASA Goddard Space Flight Center. Figure 4 is a time-series plot for daily rainfall in the Chicago area, showing a few small rain events before April 18, which saturated the ground and increased the potential for flooding when heavier rains fell a few days later. Figure 4 shows the evolution of this weather event. Prior to April 18, the region was very active with several mesoscale convective systems that produced isolated heavy rains; however, not much rainfall was actually received in the Chicago area (Fig. 4). On April 18, when a cold front arrived from the northwest, the rain areas became more organized, extending from the Great Lakes region all the way to southern Texas, and moved toward the east along the cold front. The Chicago area received much more rain than did the rest of the region as the result of the slow-moving system (Figs. 3 and 4). The excessive rains fell on the pre-saturated ground, contributing to the flooding event.
Figure 5 provides an animation of this rainfall event, with global Merged-IR Geostationary Operational Environmental Satellite (GOES) infrared (IR) brightness temperature data. The clouds associated with the successive storm systems that delivered a large amount of rainfall over a short period of time to the Chicago area can be clearly seen.
Accumulated rainfall on April 18, 2013 derived from the near-real-time rainfall product, TRMM Multi-satellite Precipitation Analysis (TMPA-RT), developed by Dr. George Huffman at the NASA Goddard Space Flight Center. (Top: units in millimeters; bottom: units in inches.) The maps were generated using the GES DISC Giovanni TRMM Online Visualization and Analysis System (TOVAS, http://disc.sci.gsfc.nasa.gov/precipitation/tovas
Figure 4. TMPA-RT rainfall time series for the Chicago area, showing a few lighter rain events before April 18. These rain events led to saturation of the ground, worsening the flooding conditions when the heaviest rains fell. The inset maps show the rainfall pattern on April 10-11 and on April 18. (Click to view full-size.)
Animation of the Geostationary Operational Environmental Satellite (GOES) infrared (IR) brightness temperature from the Merged-IR product, archived at and distributed by the GES DISC, showing the evolution of several mesoscale convective systems "training" over the Chicago area. The animation was generated with the GES DISC Hurricane Data Analysis Tool (http://disc.gsfc.nasa.gov/daac-bin/hurricane_data_analysis_tool.pl
). The half-hourly merged-IR product has a spatial resolution of 4 km, an ideal product for investigating weather events around the world (60° N - 60° S). Available time coverage is from February 7, 2000 to present.
Addendum: Does it really rain more in April in the Chicago area?
Even though April is famous for its rain showers, it actually rains more in the early summer in the Chicago area, likely due to the occurrence of more convective thunderstorms as seasonal warmth and humidity interacts with lingering cold air in this northern Midwest city. Climatological plots (Figure 6a and 6b) show that largest increases in the seasonal precipitation are in March-April, with amounts peaking in June-July.
Models of climate change, such as those examined in a recent NASA study (Lau, Wu, and Kim 2013) suggest that extreme rainfall events will become more common in the next decades, particularly in areas that already receive large amounts of rain. At the same time, other areas that commonly receive only small amounts of rainfall could get even less. Thus, using NASA data and tools to study events such as this spring flood helps refine scientific understanding of the effects of climate change.
Figure 6. (a) Global Precipitation Climatology Project (GPCC) monthly rainfall climatology for the area of the inset maps shown in Figure 4. (b) Solid line - the 1998-2012 precipitation climatology computed from the TRMM 3B43, Version 7A data product; Dashed line - the 1951-2000 rain gauge stations climatology from the Global Precipitation Climatology Center (GPCC) for the same area. The plot shows climatological means in units of millimeters of rainfall accumulated per square meter, for the particular monthly interval. Although TRMM satellite observations and GPCC have very different methodologies and temporal coverage, the two data sets are remarkably consistent. Because global precipitation is known to have been steady in the past decades, the effort to constantly improve data processing and data analysis algorithms yields more consistent precipitation records.
Reference: Lau, W.M.K., Wu, H.-T., and Kim, K.-T. (2013) A canonical response of precipitation characteristics to global warming from CMIP5 models. [PDF] Geophysical Research Letters, accepted.
Text and figures by James Acker*, Zhong Liu, and Andrey Savtchenko.
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* Grew up in Des Plaines, Illinois, and ate at the first McDonalds.